ERDAS Imagine Frequently Asked Question (FAQ)
ERDAS Imagine Frequently Asked Question (FAQ)
  • What is the best beam mode for use with the IMAGINE StereoSAR DEM module and which combinations produce the best results?
    Fine beam images with a pixel size of 6 meters would seem, at first glance, to offer a much better DEM than standard beam with 12.5 meter pixels. However, a fine beam image only covers only a quarter of the area of a standard beam image and produces a DEM only minimally better. Therefore, the best beam mode for use with the IMAGINE StereoSAR DEM module is RADARSAT standard beam mode. For optimum results, we recommend one of the following combinations of data:

    S3/S6, S3/S7, S4/S6 or S4/S7

    Also, following discussions with RADARSAT, for a cost effective solution, we also recommend using a combination of RADARSAT wide beam mode and standard beam mode. The following combination is recommended:


    The interval of time between collection dates can also be a factor if conditions such as land cover have changed significantly. Minimizing this time interval is recommended.


  • When compressing a thematic image, I get a warning. Is there an option that will keep this warning from appearing every time I am compressing a thematic image?

    (Updated 3/4/2011) Yes. This preference can be changed by going to File > Session > Preferences and selecting the MrSID Exporter category. Simply remove the check inside the box next to Warn before compressing a thematic image. Remember to click on User Save and close the Preference Editor.


  • On a Windows server or workstation, how do I determine the system ID for licensing?
    (Updated 1/8/2010) See "Determining System ID."


  • Are ERDAS IMAGINE and LPS compatible with the Linux operating system?

    (Updated 1/8/2010) No. ERDAS IMAGINE does not support the Linux OS. We are continuing to monitor the size and commercial viability of the Linux user base, and may support Linux in the future, but there are currently no plans to support Linux.  The photogrammetry product line and the extensions for ArcGIS are Windows-only. Several of the ERDAS APOLLO products support Linux, as does the ERDAS-Net 2009-and-higher license managers.


  • After importing a USGS SDTS DEM, I display the resulting .img file and the image is very dark. What can I do to fix this?
    (Updated 3/4/2011) This is very often due to a null data value of -32767 within the image. This value dramatically skews the histogram causing your image to appear either very dark or very light. The simplest solution is to recode this value to zero by creating a simple model in the Model Maker. Under Support > Utility Files, there is a spatial model to automate this process.


  • How to specify a port for licensing?
    (Updated 3/4/2011) Please see "Enabling Firewalls and Specifying Ports for ERDAS Licensing."


  • Why do I get an error during mosaic: efio_ftruncate failed?

    (1/8/2010) The "efio_ftruncate failed" is a file size error that is caused by a bug in Microsoft Windows XP Professional x32. The problem can vary from file to file and may allow you to generate very large files and then fail on another set of files. Some large processes will complete, some will not. This problem is related to limitations reported in the article There is no fix available for Windows XP Professional x32. Microsoft has implemented the fix in Windows XP Professional x64, Windows Vista and Windows 7 (all OS releases after XP Pro x32). For work with large output files, choose a Windows operating system higher than Windows XP Professional x32.


  • System ID changes for licensing
    System ID Changes: Please complete the System ID Change form (legal agreement).


  • Why do I get an error during processing in IMAGINE “not enough disk space available”, when I have plenty of disk space?

    (1/8/2010) ERDAS IMAGINE is not memory intensive (except in the 3D environment), but it is temp-space-intensive. Many common remote sensing tasks, particularly mosaicking, layer stack, resolution merge, and rectification use a lot of temporary space. In mosaicking, for example, ERDAS IMAGINE is taking all of the images and performing numerous intermediate calculations on the entire dataset in order to stitch the scenes together. We recommend that a user have available temp space of at least 2.5 times the total combined files sizes of all the input images. For example, a mosaic of ten images totaling 100 MB might need a minimum of 250 MB of free temp space to run efficiently.

    To check this in ERDAS IMAGINE, at the top of the main menu, go to Session > Preferences > User Interface and Session. About halfway down there is a setting for the location of the temp directory. It is critical that this be set to an area where there is sufficient free space. Total free space on a hard drive is not what is important. It is important that the space be available to the temp space setting. This is often set to C:\, or the default setting of $TEMP which is C:/Documents and Setting/Username/Temp. There often is not be enough space in these locations. If you have a large empty network drive available, that may work better. We generally say that a local drive is better for temp space (to avoid packets getting lost), but a network drive can work. Tip: Be sure to set your external drives to NEVER Sleep if you plan to use them for temp space with Mosaic. The default sleep setting is usually fifteen minutes which could cause a problem for really large outputs.

    Also, some users have had trouble with the disk format of network drives. If you are using Windows XP, verify that your network drives are formatted to NTFS and not to FATB or FAT32.

    You may have better success by running a series of smaller mosaics and then mosaicking them together to produce your large output mosaic. This can reduce significantly the overall number of seamlines and feathering zones and the attendant intermediate calculations that have to be performed to a more manageable level.

    Keep in mind that if you are using compressed data such as MrSID, the problem can be severely compounded. To perform any processes in ERDAS IMAGINE with compressed images, the images must be uncompressed first. In the scenario with MrSID, at 20-to-1 compression, you could be looking at extraordinary data size, enough to kill most any computer.

    Recommendations for IMAGINE 9.x temp space issues:

    1. Upgrade to IMAGINE 2010 as soon as you can. Mosaic operates much more efficiently and has less need for temp space.
    2. Complete the mosaic in sections, then mosaic the sections into the final output.
    3. Verify that your temp space directory has access to a large empty drive.
    4. If using MrSID images, convert all images to .img first, run the mosaic, then convert to .sid afterward.


  • How do I delete the ERDAS logo from my plots when I print directly from the Viewer?

    The templates are in the $IMAGINE_HOME\| Program Files\IMAGINE X.X\etc directory. You will need full permissions to make changes to the files.

    1. In a Viewer, open the *.map files.
    2. Select either the portrait or landscape .map file.
    3. Select View > Arrange Layers and right-click on the ERDAS logo layer and select Delete.


  • Why is it necessary to use a common LUT with 16-bit and IKONOS multi-segment imagery?

    Basically, 16-bit (or 11-bit treated as 16-bit) cannot be displayed on a 256 grey-level color gun, so IMAGINE generally bins the data for you into 256 bins. Where the bins occur depends upon the distribution of the input image. Even if you Direct Bin the data (as many bins as max - min), the binning occurs between the minimum and maximum data values for that image. Consequently two 16-bit images generally don't have the same binning structure and therefore it's difficult to copy breakpoints from one to another (because the breakpoint in one might not exist in the histogram of the other!).

    The ideal solution is to mosaic the two halves back together again once you've received them. Then you would have no problems. A single LUT could be used for the image mosaic.


  • What is a "scalar" variable in Spatial Modeler?

    The scalar is used as a single variable that may be included in several functions in the model. Lets say that you have five functions in a model, each with a particular value (e.g., 2) at three places within the function. You can either type the value "2" in the functions or tie the scalar variable to each function and insert the variable in the statement (in place of the value 2). The advantage to using the scalar variable is that if you want to change the value from, say, 2 to 3, you only have to change it once in the scalar dialog instead of fifteen times in five different functions.

    Thanks go out to power-user Lloyd Coulter for this concise answer.


  • How are confidence values computed in Expert Classifier?

    A confidence value is a probability that the node is significant. Confidence values for rules may be explicitly assigned by the knowledge engineer or they may be computed by the Expert Classifier from the confidence values of the conditions. Confidence values for conditions are always assigned by the knowledge engineer. Computed confidences do not override the knowledge engineer-assigned confidences. The equations below shows how confidences are computed. In the case of multiple ORs, the highest confidence is taken.

    This figure defines the across branch and along branch terms and shows how confidences are calculated from given condition confidences. In this example, there are no explicitly assigned rule confidences; all are calculated.


  • How does compression work in ERDAS IMAGINE? If I set the preference for default compression in the category "IMAGINE Image Files (Native)" to ESRI Run-Length Encoding, some processes in ERDAS IMAGINE, such as Subset, produce uncompressed output. Why is this?

    Data Prep | Subset and many other functions are based upon the Spatial Modeler. The "Data Compression" preference in the "Spatial Modeler" category offers three choices:

    None -- always produce an uncompressed result
    Run Length -- use ESRI Run-Length compression whenever possible
    Default -- use compression settings of native format

    We generally recommend "Default" so that you can use all of the native preferences in the "IMAGINE Image Files (Native)" or "TIFF Image Files" categories. The "None" and "Run Length" choices are out of date, but must remain so that people who have made a choice in the past will continue to get the results they expect.

    Note that the Viewer's "Save As" function follows different rules. If the input image is compressed, "Save As" will attempt to use the same form of compression in the output image. The native compression preferences come into play if the input image is compressed. In other words: Save As tries to mirror the compression of the input image. If you start with G4 TIFF, it will try to stay with G4 TIFF. If the input image is not compressed, then the native compression preferences come into play.


  • How do I rename or fully delete a .img and .ige file?

    (Updated 3/4/2011) ERDAS IMAGINE 8.X creates both .ige files (for files over 2 GB in size) and .rrd files (pyramid layers). The .ige and .rrd file names are embedded in the HFA structure of the image. Renaming files via the Windows or UNIX rename function will not properly rename all the associated files. To properly rename an ERDAS .img file and all its associated files, use the Image Command Tools at Manage Data Tab > Image Group > Edit Image Metadata.


  • Error in reprojection: proparameters not found

    For an image to be able to be reprojected, it must have an original projection assigned. Many images, especially TIFF images with world files, carry no actual projection information, only corner coordinates. The proparameters error message refers to the lack of projection information in the image itself. You may add projection information manually to your original images easily, if you know the original projection details:

    1. Open the image's Image Information dialog.

    2. Select Edit > Change Map Model. Add the appropriate information.

    3. Select Add/Change Projection. Add the appropriate information.

    Always add/change the map model first, then add/change the projection. The image now carries its original projection, and can be reprojected in ERDAS IMAGINE.


  • User's home drive not found, not writeable

    Regarding the installation problem, ERDAS IMAGINE is looking for the M:\ drive to find the “users” folder created during the installation in the Windows profile of the logged-in user’s home drive. In your case, it seems that the non-admin user’s Windows profile resides on a network drive. On a default Windows machine the logged-in user will have the IMAGINE directory created as C:\users. There are three options to work around this:

    1. The best option is to go into the environment variables on the workstation and create two “user environment” variables. To set the variables, right-click on My Computer > Properties > Advanced > Environment Variables. Under User Variables, select New.

    Variable1: Variable name: HOMEDRIVE Variable value: C:

    Variable2: Variable name: HOMEPATH Variable value: \

    Then create a folder named “users” on the C: drive. ERDAS IMAGINE should start as long as the license file has been loaded.

    2. Option 2 is to have a “users” directory created on that remote drive, but all users would need full access to this drive.

    3. Option 3 is to have the users log in to the machine locally where the default C:\users would be used.


    Power-user Pete Clapham offers this suggestion to use DOS to easily create a user directory on a network drive:

    a. Open a command prompt (DOS prompt)

    b. Type md x:\users assuming your network home drive is x:.


  • What are the BIK and BIK! data order types?

    BIK and BIK! are data order types added starting with IMAGINE 8.7. BIK means Band Interleaved by blocK and the ordering is similar to that of tiled BSQ. BIK! means that the format DLL requires the data to be presented in order. The upshot is that if you raster edit this file, a dump file will be created and the entire image will be re-written. If the format is BIK, the dump file will be avoided.


  • Why am I not able to orthorectify using ROP/RPC model in AutoSync Workstation with Quickbird data?

    Check that you have orthoready imagery by opening the metadata file, the *.IMD file, in a text editor such as Wordpad. An *.RPD file will come with orthoready imagery.

    Sample IMD Metadata file excerpts:

    productLevel = "LV1B"    (Works if RPD file is available)
    imageDescriptor = "Basic1B"

    productLevel = "LV2A"    (Fails)
    imageDescriptor = "Standard2A"

    productLevel = "LV2A"    (Works)
    imageDescriptor = "ORStandard2A"


  • Help files do not display, only an "x" appears

    This problem usually happens when there is no Java Virtual Machine installed on the computer. To solve this, you can point your browser to the following URL and follow the wizard to download and install the Java Virtual Machine:

    Note: You will have to reboot your machine before the changes take effect.


  • How to export pixel data to Microsoft Excel?

    Two methods:

    1. Image info - Pixel View. Highlight the rows/columns that you want to load into Excel, Click Copy, point at the Excel table, click Paste.

    2. Utilities - Convert Raster to ASCII. Rename the output from .asc to .txt, open directly in Excel as fixed space delimited. Excel is limited to ~ sqrt(64000) rows and columns. If you have a large multiband image it may not fit within Excel.


  • When I open a RGB TIFF file from ERDAS IMAGINE in Photoshop, the image appears panchromatic (black and white).

    In ERDAS IMAGINE, the default for TIFF export is set to multispectral. You must select the RGB option when exporting a TIFF from ERDAS IMAGINE in order to view in Photoshop or most other image processing software. The default can be changed to RGB under the TIFF Preferences, in the Export band selection option. Newer versions of Photoshop can handle multispectral TIFF images.


  • What is the relation between the files/folders containing the .gdb extension created by ERDAS IMAGINE and ArcGIS 9.2?

    You may have noticed on your file system that ArcGIS creates folders with a .gdb extension, while ERDAS IMAGINE creates files with a .gdb extension. Each of these is a geodatabase, however, they do not conflict with each other. The .gdb folder contains the new File Geodatabase implementation by ESRI. The file geodatabase folder is similar to the Personal Geodatabase, but it has a .gdb extension instead of a .mdb extension. The .gdb files are proxy files that Leica Geosystems uses for their implementation of a personal geodatabase.


  • How do I display an image in the Map Composer without a standard deviation stretch?

    The ERDAS IMAGINE Viewer has a default two-standard-deviation stretch. An image displayed without a standard deviation stretch in the Viewer will still display the stretch after the map composition is closed and opened again. It is necessary to save the ‘no stretch’ to a lookup table (LUT) or permanently to the file. Please follow the following steps:

    1. Open the image without a stretch in the Viewer.
    2. Go to Raster | Contrast | Breakpoint Editor and the histograms will not show a stretch.
    3. Apply this either to a LUT or to the image file.
    4. Save the image in the Viewer.

    When opening this image in the Map Composer, it will now always be displayed without a stretch.


  • I’m having trouble connecting to my Geodatabase for Arc GIS 9.1+. What could be the problem?

    There have been numerous reports of ERDAS IMAGINE failing to connect to Geodatabases on systems with ArcGIS 9.1 and above. The most common symptom of this problem is that the Geodatabase file-chooser dialog is displayed, but not populated.

    This problem is circumvented by locating fmearcgisext.dll in your ArcGIS install directory and renaming it to something else (for example, _fmearcgisext.dll). Once ERDAS IMAGINE is restarted, the geodatabase file-chooser dialog should then populate normally.

    The cause of this problem is a known bug in ESRI’s ArcGIS software. Discussion on this problem, along with associated tracking numbers, can be found at ESRI’s message boards, at the following link:

    As seen from the above discussion, the problem is caused by bad interaction between ArcGIS and SAFE’s FME ArcGIS extensions. Consequently, it should be noted that renaming the aforementioned DLL will disable these extensions.

    This problem is localized to ESRI’s software, and is not observed when the IMAGINE Geodatabase support CD is used instead of an ArcGIS installation.


  • Do I need to be an expert hyperspectral user to use the IMAGINE Spectral Analysis tools?

    ERDAS FAQ - facegis.comNo. An over-riding concept of the software is ease-of-use with an easy workflow and intelligent data-derived defaults. For the analyst who is not an expert in hyperspectral remote sensing, easy access to spectral analysis is via the Task Workflows, a wizard-based process. For this approach the analyst simply determines their object or task: Anomaly Detection, Target Detection, or Material Mapping.


  • When I try to save any edits to the TIFF header information, I receive an error message indicating that the TIFF file may not be deleted because it is in use by another application. How may I save these edits?

    When editing image header information for a TIFF file, such as map or projection information the TIFF file that is being modified may not be simultaneously displayed in a viewer. If you attempt to save edits to the header information for the TIFF while it is displayed, you will receive the following error message:

    ERDAS IMAGINE locks the TIFF file while it is displayed in a viewer. Even if the “Edits Allowed” preference is enabled you will not be allowed to edit the file when it is displayed in a viewer. To correct this, clear the TIFF file from any ERDAS IMAGINE Viewer to allow the edits to be saved. It is possible to edit the image information for a file without displaying it in a Viewer. This is possible from the main ERDAS IMAGINE toolbar Tools | Image Information. This will allow you to open an Image Information dialog window for an image file, without the Viewer ever being opened.


  • How can I rotate a vector coverage which is overlaid on a raster image?
    In the Viewer menu, go to Utilities | Selector Properties. First, go to Vector | Enable Editing. Next, select the points, lines, or arcs you wish to rotate. Enter the desired rotation angle in the RotBox Editor and select OK.


  • When I try to use TIFF images in ERDAS IMAGINE processes, I get an error that states that the TIFF images are read-only. All my TIFF files have full read/write permissions. What is going on?

    ERDAS IMAGINE contains internal preferences for TIFF images. One of the preferences allows the user to select whether or not to allow edits to TIFF files. To change this setting, go to the very top of the ERDAS IMAGINE main menu and select Session | Preferences. In the Preference Editor, select the TIFF Image Files category, and verify the Edits Allowed check box is selected. The Edits Allowed preference determines whether or not you can edit a TIFF file. If you allow yourself to edit TIFF files, keep in mind that any TIFF tags that are not part of the Baseline TIFF specification may be purged from the file as the TIFF specification directs.


  • In the Knowledge Engineer, how do I create AND statements and OR statements?

    There are several different ways of setting up hypothesis. These involve setting up criteria rules based on variables.

    You have probably found that it is possible to ‘And’ the criteria set in a rule from the Rule properties dialog box. This brings up a Cell Array where any number of criteria based on variables can be set. The criteria set in this dialog box relates to a single rule and they need to be satisfied for the rule to be satisfied i.e. an And statement is being used. From within the Rule Properties, it is only possible to AND the criteria.

    This is an AND rule, all the conditions or criteria based on variables (cyan) that have been set up in the Rule (yellow) need to be satisfied for the Rule (and therefore the hypothesis) to be satisfied. In the Rule Properties dialog, notice that in the top left corner of the Cell Array the cell contains AND. This is an easy way to identify this type of rule.


    ANDing is at a variable level - where if there is more than one condition in a rule set using different variables then both conditions must be true for the rule to be true.

    If you wish to use an OR statement, it is necessary to set up a separate rule for each criteria which you need to check in order for a Rule to be satisfied. The OR Statement is at the hypothesis level. If either rule is satisfied then the hypothesis will be satisfied.

    This is the OR rule: For the Rules to be satisfied all the conditions or criteria based on variables (cyan) that have been set up in the Rule (yellow) need to be satisfied for the Rule to be satisfied.

    Here we have two Rules leading into the same Hypothesis. This is the OR Rule: either of these two Rules could be satisfied in order for the Hypothesis to satisfied. They do not necessarily both have to be true.


    ORing is at the hypothesis level where there is more than one rule for the hypothesis; either rule needs to be satisfied for the hypothesis to be satisfied.

    Remember: The AND Statements are at the Rules level and the OR statements are at the Hypothesis level. See the example below:

                        ------- Criteria based on variable

    ----- RULE (AND)

                        ------- Criteria based on variable


              ------ RULE           ------- Criteria based on variable


                        ------- Criteria based on variable

              ----- RULE (AND)

                        ------- Criteria based on variable


  • I can no longer read a *.map file. How do I edit a pathname in a map composition file?

    Go to Map Composer and select Edit Composition Paths.

    The Map Path Editor will open. In this dialog you will be able to specify the frame to be edited and the image location.


  • When I try to print multiple images from a single Viewer in a map composition I get black output in the mapframe. Why?

    When adding multiple images into the Viewer to be brought into the map composition, make sure that the ""background transparent"" checkbox is enabled under the Raster Options tab.


  • I’m logged in as administrator on my PC but I still can’t run the batch functions in ERDAS IMAGINE. What is the problem?

    Please ensure that the Task Scheduler service is running:

    Go to the Windows Services dialog and ensure that the Task Scheduler service is started and set to automatic.


  • How can I update an existing landcover classification with new classification information and maintain the extent of the original image?

    You will need to create a simple model. In Model Maker, create a model that has two input raster objects, one function object, and one output raster object. Join the two input raster objects to the function and then the function to the output raster object. Define one input raster object to be your existing landcover classification image and the other input raster object to be your new landcover classification image. The model will look something like this:

    The function to use is a Conditional EITHER statement. The function statement to use to accomplish this task will look like this:

    EITHER (New Classified Image) IF (New Classified Image !=0) OR (Existing Classified Image) OTHERWISE

    This model will also work if you wish to substitute information from one image into another.


  • When running the Perimeter function (Interpreter | GIS Analysis | Perimeter…), how is the perimeter calculated?

    The algorithm used for the Perimeter function is based on Dana Tomlin's algorithm in ""Geographic Information Systems and Cartographic Modeling""

    The example below shows four different AOI’s on 30 meter pixels.

    When looking at the perimeter, consider the surrounding pixels and how a splined vector boundary would fit (represented by AOI layer).

    AOI 1: 84.852 – the pixel is completely surrounded by 1 value (giving a circular perimeter)

    AOI 2: 102.426 - the pixel is surrounded by 2 values (giving a elliptical perimeter)

    AOI 3: 111.213 - the pixel is surrounded by 3 values (giving three 90 degree corners and one elliptical side)

    AOI 4: 120 - the pixel is surrounded by 4 values (giving a square perimeter)
    Also see the technical note "Rules for Pixel Inclusion Within Polygons".


  • When using the Spatial Modeler, I get an error that says “Divided by zero”. How can I avoid this?
    In order to be able to divide by zero in the Modeler, you need to define your inputs as floating point data.


  • The Spectral Analysis wizard-based tasks are easy to use, but I’d like a more hands-on interface to work with my data. Is that possible?
    Yes. An alternate access to the functionality of the IMAGINE Spectral Analysis software is the IMAGINE Spectral Analysis Workstation. This workstation provides an interactive interface to all the Task Workflows as well as viewing tools and greater access to algorithm inputs.


  • Can I use the batch function to perform processes like reprojection?
    Yes. The batch function is particularly useful for processes which may take a long time. The Data Prep | Reproject Images and Batch tools in ERDAS IMAGINE give you the capability to reproject multiple images in minutes, cutting out the down time in setting up the reprojection parameters for each individual image. The reprojection parameters only have to be defined once before the Batch Wizard provides the flexible tools to perform the same operation on multiple files. The input files you wish to reproject, can be populated in a variety of ways. You may select individual files, or specify a pattern to select multiple files (such as atl*.img, which would select all *.img files that start with the prefix “atl”). The Batch Wizard saves time by processing multiple jobs concurrently, or a specified time and date can be set for the start of the job.


  • Do TIFF images have a file size limitation?

    Yes. IMAGINE 8.7 follows the newer TIFF 6.0 standard, which permits TIFF images up to 4.0 GB in file size.  In IMAGINE 8.6 and earlier versions, the TIFF specification limits the file size of TIFF images to 2.1 GB.


  • I created tiled TIFF images in ERDAS IMAGINE and compressed them with the MrSID compression utility, and now there is a black stripe at the right side of the image. What causes this?
    When you are using tiled TIFF files with the MrSID compressor, the resulting *.sid file contains a black stripe at the right-hand side of the image, that is, the image data is changed to black pixels (approximately 10 pixels in width). The black stripe does not appear when TIFF files are used that are not tiled. To avoid this black stripe, it is necessary to use the ERDAS IMAGINE Preference Editor to disable the Create Tiled Images preference in the TIFF Image Files category.



  • I have a TIFF world file from an ESRI application. How can I read this into ERDAS IMAGINE?

    ERDAS IMAGINE 8.3 recognized TIFF World Files (.tfw) as providing rough map information for TIFF images. This information was used as a fallback source of map information if there were no georeferencing tags in the TIFF (.tif) file itself (i.e., it wasn't GeoTIFF). In other words, after being told to open a .tif file, ERDAS IMAGINE first looks in the TIFF file itself for GeoTIFF tags. If these are absent, it looks for the simpler .tfw file, then just reads the image's file coordinates if neither are present.

    ERDAS IMAGINE 8.4+ will do this for ANY type of image it is told to open (even for .img files). The software will first look for georeferencing information within the file format itself (e.g., the HFA georeferencing nodes in an .img file), and if these aren't present it will look for a World File (e.g., .igw) with the same root name, then treat the file as file coordinates if neither of these are present.

    So, as an example, you could open a JFIF file (e.g., lanier.jpg). JFIF does not support georeferencing in the format itself, so ERDAS IMAGINE would look first for a World File (called, in this case, lanier.jgw) and use that for map info. Otherwise the file will be read as raw file coordinates.

    Arc World Files can be created as well as read by ERDAS IMAGINE 8.4+. A source of georeferencing map information is required - if no image already exists with this information, you may have to resort to a text editor and create the relevant world file manually. However, if you have an image with full georeferencing information, ERDAS IMAGINE 8.4+ provides the Image Command Tool for creating a world file (among other things) from the header information of an existing image file. This provides a convenient feature even if the image file already has projection information (which is more complete than a World file can store). As an example, you may want to pass the image to an application that doesn't recognize the georeferencing information stored within the file format itself. For instance, many applications do not recognize GeoTIFF georeferencing information, but may read a TIFF World File. So, having created a GeoTIFF file in ERDAS IMAGINE 8.4+, you can use the Image Command Tool to select that GeoTIFF file and automatically generate a TIFF World File with the .tfw extension to go along with the GeoTIFF .tif file. The other application, which doesn't know how to interpret GeoTIFF georeferencing tags, then ignores the tags and uses the .tfw file to supply map information instead.

    This ability can be combined with the Batch Wizard to automate the production of hundreds of World file-style images.


  • Which TIFF file version does ERDAS IMAGINE support?

    ERDAS IMAGINE 8.4+ supports TIFF version 6.0, including those TIFFs which conform to GeoTIFF version 1.0.


  • What is the GeoTIFF standard?
    GeoTIFF represents an effort by over 160 different remote sensing, GIS, cartographic, and surveying related companies and organizations to establish a TIFF-based interchange format for georeferenced raster imagery. For a full description of the standard, see the GeoTIFF website.


  • What are the ERDAS IMAGINE file name extensions?
    For full file extension name information, please see the help file located at <IMAGINE HOME>help\html\imagine_interface\file_specifications.htm.


  • I want to scan-in a hard copy image. How big will the resultant image file be?

    We will assume a black & white aerial photograph to be scanned as a single-band image for this example. You need to know:

    • Size of image in inches or centimeters (e.g., 9x9 inches)
    • Dots per inch (DPI) of the scanner to be used (e.g., 600 dpi)
    • Bit level of scan (e.g., 8-bit scanning).

    For example, a 9 x 9 inch standard aerial photograph, scanned at 600 DPI, at 16 bit can be calculated as:

    • 600 dpi * 9 inches = 5400 pixels wide
    • 600 dpi * 9 inches = 5400 pixels high
    • 5400 wide * 5400 high approximately = 29.16Mb
    • For 16 bit data, multiply the result by 2.

    Therefore, each image will be approximately 60Mb in size. If you were scanning a three-color aerial photograph, multiply this number by three to account for the extra bands in the data.

    Note: Pyramid layers, if calculated internally to the IMG file, can potentially be 30% of the original image size.


  • How does ERDAS IMAGINE for Windows and Sun Solaris import MrSID files?

    MrSID is Multi-resolution Seamless Image Database (MrSID). It is a wavelet compression technology and data format developed by LizardTech. This patented format provides a significant reduction in the disk space needed to store high-resolution images while maintaining the quality and integrity of the original.

    ERDAS IMAGINE for Windows and Sun Solaris can read images produced by versions 1.2, 1.3, and 2.0 of the MrSID Compressor. For more information on MrSID or LizardTech, visit the LizardTech web site.

    In ERDAS IMAGINE for Windows and Sun Solaris, you have direct-read capability through the Viewer. Simply specify the data type as MrSID and load the imagery into the Viewer. If you would like to create an IMG file from the data, simply reset the zoom to 1:1, , and select File | View to IMG from the ERDAS IMAGINE Viewer.


  • What is the *.ige file and why is it so large?

    The .ige file has been developed for ERDAS IMAGINE data files so that you can handle images greater than the file size limitations imposed by the operating system. Before version 8.4, the *.img file was limited in size to being less than 2.1 GB. With the addition of the .ige file, ERDAS IMAGINE no longer limits the size of file that you can create; it is now dependent on your operating system. When creating an image larger than 2 GB in size, the default settings will create a *.img file to store header information, and then use an *.ige file to store the imagery itself.

    For example, if trying to mosaic together a large number of aerial photographs that would amount to 50 GB of raster data, ERDAS IMAGINE 8.4+ will produce a small *.img header file and a 50 GB *.ige file.

    Why was the support for larger than 2 GB images done this way? To preserve backward compatibility with applications which only read *.img files smaller than 2 GB. For instance, there are many third-party products which can import or directly read *.img files. If we simply changed to 64-bit addressing, these products would no longer be able to read the new *.img files, even if those files were less than 2 GB in size. With this backward compatibility, third-party applications can still read the *.img files, if they are less than 2 GB.

    The Reserve Non-Raster Space preference [IMAGINE Image files (Native) category] sets the amount of space in the .img that is set aside for header information. In determining if an .ige file is required, ERDAS IMAGINE calculates the total size of the raster data, plus the amount of reserved non-raster space, and compares this value to the file size limit set by the operating system. If the value is greater, then a .ige file is created to hold the raster data.


  • Does ERDAS IMAGINE have a file size limitation?


  • What is the *.aux file?
    The .aux extension indicates an auxiliary file, mainly used in conjunction with non-ERDAS IMAGINE files accessed by the Raster DLL, to store information not normally supported by the particular raster format. The TIFF file format, for example, does not store image statistics, so statistics generated by ERDAS IMAGINE are stored in an .aux file with the same prefix name as the .tif file.


  • What is the *.rrd file?
    The *.rrd file is an external pyramid layer that was created by successively reducing the image by the power of 2 and resampling the image. Pyramid layers enable the Viewer to display large images more quickly. RRD stands for reduced resolution dataset.


  • How can I locate my lens flare?

    In a VirtualGIS Viewer, open View | Sun Positioning… and Navigation | Position Editor. Change the sun position azimuth and pitch to be the same as the position editor azimuth and pitch, respectively, or vice versa. Click Apply in the tool (the sun positioning or position editor) that you changed and you should be perfectly aligned with the lens flare.

    Note: Currently this does not work with Lat/Long DEMs.


  • How can I view the smooth transition from day to night?
    To view the view the smooth transition between day and night, add one element as Most visible during the day and the other as Most visible during the night. In the VirtualGIS viewer, click View | Sun Positioning. Adjust the elevation control to view the transition. Use the pull-down menu in the Panorama Builder under the options tab to change the Day/Night transition between always visible, slow fade, medium fade, or fast fade.


  • How can I use the Sky System feature to create a panoramic view in the VirtualGIS Viewer?

    Within a VirtualGIS Viewer, display the imagery you would like to use as your panoramic background. Save the view to an image file. Click on the Options tab and check Create Panoramic Images. Deselect Maintain Aspect Ratio if you would like the number of rows and columns of pixels to stay in proportion with the width and height of the viewer. The output image size pixel number must be in multiples of 2; 512 x 512 is recommended. Click OK. Six individual images are created, each of which represents the inside of a cube. These six images have the view to image file name followed by an underscore and a number that associates to a side of the cube.

    Display your desired data in a VirtualGIS Viewer. Open the scene properties and click on the Background tab. For the background type choose Panorama. Click on the Create New button. Name the .pan file and click OK. The Panorama Wizard displays. Follow the instructions in the wizard dialogs to either load the 6 images created earlier (select any of the 6 images and IMAGINE will place them in the wizard in the correct order as they were generated when saving the view to an image file), or a 360 or 180 degree panorama map. You are then prompted to add environmental elements, such as clouds or stars, and define their visibility and motion. The Panorama Builder allows you to view each layer and change element properties. You may reopen the wizard at any time to add panoramic maps or elements, but make sure you are adding the proper file in the appropriate dialog. For example, if you reopen the wizard and wish to add an element, you must click Next 3 times to proceed to the proper dialog. In the VirtualGIS Viewer, select Navigation | Enable Constant Update. The elements will then move according the way they were defined (fast, medium, or slow) and the wind speed and direction.


  • How can I extrude polygons and add textures to my 3D shapefiles after digitizing them in Stereo Analyst?

    Once you have features digitized in Stereo Analyst, you must export the them to 2D and display the shapefile in a viewer. Make sure editing is enabled through Vector | Enable Editing. Select Vector | Attributes. In the Attributes dialog, select Edit | Column Attributes. Click New to create a new column called Height. Change the type and adjust the width of the column to correspond with your data. Create two more columns for the side and roof textures and name them, e.g., ""side_text"" and ""roof_text"". These columns will be String data. Adjust the width of the new columns to fit the path name for the associated textures. Next, enter the new column information by entering the height values and pathnames of the textures into the Attributes dialog. Save the file.

    Open a VirtualGIS Viewer. Display the shapefile and within the file chooser dialog click on the Vector Options tab. Choose Extend Vertically from the pull-down menu. Under the Polygon Height Attribute select height, and the title of the new texture columns to correspond to the Side and Roof Texture Attributes. Click OK. This will display your extruded polygons with textures.


  • What is a Virtual World, and why should I consider creating one?
    IMAGINE VirtualGIS 8.4.1 and newer versions contain a very important feature called the Virtual World Editor. Creating a Virtual World allows the user to display data in multiple resolution mode, which renders details close to the observer at high resolution, and distant details are rendered at low resolution. This improves performance by reducing required computations and also allows IMAGINE VirtualGIS to take advantage of multi-threading (see technical note on multi-threading). Because only some of the sectors display in high-resolution at any moment, real-time rendering is possible while moving through a Virtual World.


  • How do I create a virtual fly-through with IMAGINE VirtualGIS?
    1. Start by loading a DEM and a raster image into an IMAGINE VirtualGIS Viewer.
    2. Select the Show Data Layers in an IMAGINE Viewer Without Linking icon. This loads your data into an ERDAS IMAGINE standard Viewer.
    3. Select Navigation | Flight Path Editor from the pull-down menu.
    4. In the Flight Path Editor, select the Digitize Flight Path icon. You will be prompted to click in the standard Viewer. Digitize your flight path. Simply click to place a vertex, and double-click to end your path (This is the default preference setting. A middle mouse button option is also available).
    5. You will see that the positions have been added to your Flight Path Editor.
    6. Select the Apply Changes to the Flight Path icon to update the flight path.
    7. To view your fly-through, simply press the Start Flight (play) button on the Flight Path Editor, and your flight will be displayed in the IMAGINE VirtualGIS Viewer. You may edit position, speed, view angles, etc., in the Flight Editor in order to create the desired effect. Simply save these changes and update them in the editor as you progress.


  • Can I use image subsets as input into OrthoRadar?

    Yes. You can use subsets of radar imagery as input into OrthoRadar. However, the way in which the subsets are created is important.

    The dedicated radar importers are capable of creating scene subsets, which can be processed by OrthoRadar. If image subsets are required for your input to OrthoRadar, do NOT use IMAGINE utilities such as Subset Image under Data Preparation. Use the subset option of the radar importer instead.

    An alternative option is to use the entire scene as input into OrthoRadar but during the Resample process, specify the output corners to produce a subset output.

    Note: The same applies if image subsets are to be used in either StereoSAR of IFSAR for DEM generation.


  • I originally imported my Radar data using one of the dedicated Radar importers but have since filtered the image. The header information is not present in the filtered image and I want to use the filtered image in OrthoRadar, but I receive the error message "Error invalid model passed as argument." Is there anything that can be done?

    The header information is required for sensor specific geometric modeling, which is used by OrthoRadar, StereoSAR and IFSAR. Using the dedicated RADAR importers will automatically populate the image header with all the necessary information.

    If any filtering is carried out on the image after import, such as Speckle Suppression, then the header information is lost. Without the header information, OrthoRadar, StereoSAR and IFSAR will no longer be able to process the imagery. There is a very simple solution to this and it basically involves copying the Generic SAR Node (or header information) from the original image to the new filtered image.

    You will need to access Radar | Generic SAR Node. (This option is available with any of the Radar Mapping Suite Modules, i.e., OrthoRADAR, StereoSAR and IFSAR).

    Input SAR Image Filename (*.img)
    You can use the Open icon to access a file selector. From there, you navigate to the directory that contains the image (IMAGINE format) that you want to access using the Generic SAR Node.

    • Here the original image that has imported with a dedicated importer should be selected, i.e., the image you are copying the header information from.

    Transfer SAR Image Filename (*.img)
    You can use the Open icon to access a file selector. From there, you can navigate to the directory and select the (IMAGINE format) image to which you wish to attach the Node displayed in the Generic SAR Node Tool.

    • Here the filtered image should be selected, i.e., the image you want to copy the header information to.

    Click Transfer once you are satisfied with the edited orbit information to transfer it to the Transfer SAR image.

    Now, simply click transfer to copy the header information across.


  • How do I import Single Look Complex data (either RADARSAT or ERS) into ERDAS IMAGINE for use with the IMAGINE IFSAR DEM module?

    Two input files are required for input into IMAGINE IFSAR DEM, a reference image and a match image. These need to be input as *.img files. Therefore, original radar data needs to be imported into ERDAS IMAGINE. For use with the IMAGINE IFSAR DEM module, the data needs to be imported as two separate integer layers (one for magnitude and one for phase). Data options available in the ERDAS IMAGINE dedicated importers allow for this option.

    RADARSAT Single Look Complex (SLC) and ERS-1 and ERS-2 Sensor Data, Single Look Complex (SLC) can be imported into ERDAS IMAGINE using the dedicated importers.

    There are currently five ERS import options, which relate to the ERS Data receiving stations. To import ERS data you need to know the correct ground receiving station for your data. If you do not know which ground receiving station the data is from, select any of the five import options and give and output filename and click OK. In the Import ERS (CEOS) window the SAR Image Info is displayed and the country is shown. Cancel this and start the import again choosing the correct importer for the ground receiving for your data.

    After selecting the correct importer and selecting an output filename, click OK. Then, in the Import ERS (CEOS) window, select the Data Type Options tab. This gives options for loading Single Look Complex (SLC) data. To use SLC in IFSAR, select the first option “Load as two integer layers (magnitude, phase)”. Click OK and then Import. This will load the imagery into ERDAS IMAGINE in two bands, magnitude and phase. IMAGINE IFSAR DEM uses the magnitude layer to assist in unwrapping the phase data to obtain the elevation data.

    Importing RADARSAT data is very similar. There are three RADARSAT importers for the three ground receiving station supported by ERDAS IMAGINE. The correct importer needs to be selected and, as with ERS data, under the Data Type Options tab, choose to import the data as two integer layers “Load as two integer layers (magnitude, phase)”.


  • How do I know which image is the reference image and which images is the match image in IMAGINE StereoSAR DEM?

    For the RADARSAT beam positions, S1 is the beam position nearest the nadir and S7 is furthest from the nadir. The reference image is the image which is nearest the nadir, i.e., the beam position with the lowest number. Here the sensor will be closer to the imaged area. If, for example, the pair of images was RADARSAT S2/S7, then the image with the lower number S2 should be used as the reference Image.

    The IMAGINE StereoSAR DEM module has built-in checks that assure the sensor associated with the reference image is closer to the imaged area than the sensor associated with the match image. If the reference and match images are selected incorrectly, a warning message will appear.


  • In the IMAGINE StereoSAR DEM module, if you are using ground control during the input stage to adjust the sensor orbit, is it necessary to correct the orbits of both the reference and the match image?
    You certainly could correct just one image but that would give you one ‘corrected’ orbit and one original ‘uncorrected’ orbit. This will not produce the optimum results achievable with two ‘corrected’ orbits. There is not really any gain in just correcting one. However, if you only had one GCP and it was only on one image then it would certainly be better to correct one orbit, but this is not optimum.


  • What is NASA's Stokes-matrix-compressed imagery, and how do I import it?
    The Stokes matrix is a format devised by NASA JPL scientists for compressing full polarimetric data, such as AIRSAR data. They also provide a software package for uncompressing and creating various polarization images (such as HH or HV). This software is free and downloadable; contact Ellen O'Leary at The JPL software creates a generic raster image and supplies information such as the number of rows and columns. It is then quite easy to import the product image using the generic binary importer in ERDAS IMAGINE 8.X. This product image can be used with ERDAS IMAGINE functionality as a simple raster image. If you want to use any of the IMAGINE Radar Mapping Suite tools, then the Generic SAR Node becomes necessary, and is available in ERDAS IMAGINE 8.4+. This node can be populated by manually extracting the necessary parameters from the Stokes header. It is used for reconstructing ephemeris header information on images.


  • Our images are dark, so the overlaying vector doesn't show up well. Is there any way I can have the vectors display initially as some color other than black?
    ERDAS IMAGINE has a symbology file that can be added when you open a vector coverage. The symbology file (*.evs) can be saved when you select Viewing Properties from the IMAGINE Viewer's Vector pull-down menu. After you adjust the colors in Viewing Properties dialogue window click the Save button and a Save Symbology As... window will open. Name the file and then select OK. The next time you open the vector coverage in an IMAGINE Viewer choose the Vector Options tab and enable the Use Symbology option. Select the Set button and then add your *.evs file.


  • Are there any limitations to the content of an ArcInfo coverage?

    · 500 vertices per arc

    · 500 arcs per node

    · 100 points in a polygon

    · There are no limits on the number of features in an ArcInfo coverage


  • My Viewer crashes when I enable editing on a vector coverage. How can I stop this?

    This is caused by a corrupt personal workspace in c:/users/info. To edit arc coverages, ensure the following:

    Session | Preferences | Vector – scratch directory '.'

    This now uses c:/users as a working directory. If you experience a crash when enable edit is invoked, then remove the info directory (assuming that there are no coverages in c:/users). When editing is next invoked, ERDAS IMAGINE will ask if you wish to convert c:/users into a workspace. Choose YES.

    Because the edit process has previously crashed, you will be left with XX files in c:/temp. It is safe to delete these files.


  • How do I copy an annotation created with the rectangle tool to a vector coverage?

    It is not possible to copy an annotation feature created with the rectangle or ellipse tool to a vector coverage, since there is no such object as a ""rectangle"" in vector (nor ellipse). To form a rectangle in an arc coverage it is necessary to manually work out what the four coordinates of the corners are in order to draw a rectangle. Whereas in annotation these are true constructs - to make sure they are right-angled, all that is stored is a center point with a width and a height (and perhaps a rotation angle). This way, when editing one it will always remain a rectangle (unlike editing a coverage). For points, lines and polygons, the object is stored as a set of vertices - these can simply be copied to a coverage to form the equivalent ArcInfo vectors. For a rectangle (or ellipse) there are no vertex coordinates to simply copy across, so the libraries that do this for points, lines and polygons will not work. So it is therefore not possible to copy rectangles or ellipses to a vector coverage.

    Stereo Analyst has tools for forcing right-angle corners when digitizing polygons.


  • I have features in an ESRI ArcInfo coverage that I wish to use as variables. How can I select these values in the vector coverage using IMAGINE Expert Classifier?

    Vector data can be used as variables in the Knowledge Classifier. Variables defined as feature layers may be annotation layers, shapefiles, SDE vectors, or ArcInfo coverages. It is not possible to use vector coverages directly as a single variable input into an expert classification. In order to use vector data within the Knowledge Engineer it is necessary to rasterize the vector coverage before it can be used in the classification process. There are two different ways to carry out the rasterization process:

    1. Works only for ArcInfo coverages: The coverage can be converted to a raster layer using the Vector to Raster… function from the Vector Utilities menu on the main ERDAS IMAGINE icon panel. It is then possible to specify the resulting raster image as a variable in the Knowledge Engineer.

    2. It is possible to specify vector data as variables within the Knowledge Classifier, however these vector variables have to be used as inputs to Spatial Models. These Spatial Models can then be specified as variables in a rule. Therefore the vector rasterization occurs in the Modeler and not in the Knowledge Classifier.

    Using the Spatial Modeler, define the following:

    Input vector: Make sure that you set the pixel size and the cell value.

    Function: Simply select the vector input, it is not necessary to apply a function although you can if you wish.

    Output: Set the output file name and necessary output options.

    To use the graphical model in the Expert Classifier:

    Create a new variable in the Knowledge Engineer, choose the graphical model option and select the desired model.


  • IMAGINE Subpixel Classifier - When preprocessing very small imagery (for example, a 54 x 44 pixel image) the process sometimes fails, but it will run successfully on the much larger, original imagery, why does this happen?
    The preprocessing may fail because there are too few pixels to have enough variation.


  • How do I add a new field in Image Catalog?

    It is not possible to add a new field to an existing Image Catalog. However, you can create a new catalog with an additional field and then copy the data held in the existing catalog to the new catalog.

    To do this, open a New Catalog (*.ict). In the ‘New Catalog’ dialog, enter a filename, select the Custom... button, then select OK. This will open the ‘Custom Field Definition’ dialog. In the Field List, there are a certain number of default fields which ERDAS IMAGINE requires, but it is also possible to add new fields. Simply enter the new field name and other details and then select Add Field. The new field name will be added at the bottom of the Field List. Select Close and then OK. The new field should be one of the column headings in the Image Catalog.

    If you have an existing Image Catalog and you wish to add a new column, you will need to create a new catalog adding the new field as described above. You can copy the data from one catalog to the empty catalog. You will need to ensure that the field columns are listed in the same order in each of the Image Catalogs. Then select all the columns in the CellArray of the existing catalog, then right-click in one of the column title cells and select Export. Save the data to a .dat file. Open the new catalog, right-click in one of the column headings and select Import. Select the .dat file, then OK. The new catalog will then display the same listing of images but with an additional field, to which you may now add data.


  • How can I display my entire fourier transform image in the Fourier Editor viewer?
    The Fourier Editor viewer can be stretched out to fill your entire screen. However, the full Fourier transform image can only be seen if it is small enough to fit in a full sized viewer - otherwise scroll bars would appear at the edges of the viewer. Fourier transform images are generally very large. It is not necessary to see the whole Fourier transform image as it is mirrored and the tools/filters will operate in this way. Unfortunately, this is how the software is designed. It is likely that users will be unable to see the entire Fourier transform image.


  • When running the Matrix function (Interpreter | GIS Analysis | Matrix…) the following error is received: “negative size window or zero input to global function” The program then exits and no file is created. What does this error mean?
    This error will occur when there is no common area between the two input images or vectors for the matrix function to work on. Ensure that there is an overlap area between the input files.


  • Where can I find the Tasseled Cap transformation coefficients for Landsat 7 data?
    You can find a spatial model on the Support > Utility Files section of this web site that provides the coefficients for Landsat 7 ETM+ imagery. These coefficients were developed using the method employed by Kauth and Thomas (1976).


  • Can I use UNICODE-standard 2-byte fonts (Chinese, Korean, Japanese, etc.) when creating annotation layers in the Viewer and in the Map Composer?
    Yes. ERDAS IMAGINE 8.4+ supports 2-byte fonts for annotation layers, and these fonts may be freely used in any annotation layer in ERDAS IMAGINE 8.4+. Other non-annotation functions in ERDAS IMAGINE 8.4+ are not based on the UNICODE standard, and do not support 2-byte characters.


  • My map composition turns grey when I export to JPEG. Why is this?

    Statistics are not being generated for the image and its new map composition background.

    1. Before exporting to JPEG select Tools | Image Information,
    2. Select Edit | Compute Statistics.
    3. Save these newly generated statistics.

    When exporting, use raw values when possible.


  • How do I make my own map composition templates?

    Create a map composition of your own including imagery.

    1. Select View | Arrange Layers and right-click on the image frame and select Descend into.
    2. Right-click once more on the image and select Delete layer.
    3. Save this *.map file, giving it your own file name.
    4. Use this file when making a plot from the Viewer.


  • How can I print a map composition to a PostScript file?


    You can set up your printer configuration port to 'FILE' in the Windows printer properties. This will allow you to output your map to a PostScript file. When you print your Map Composition, you will be prompted for an output PostScript file.


    In the ERDAS IMAGINE Configuration Editor, you can set the ‘Printer Connection’ to ‘File’. Also, set the options ‘Output Directory’ and ‘Output File’ as desired. (These fields are the default output locations.) When you print your Map Composition, you will be prompted for an output PostScript file. Note: Further information on configuring a printer is available in the ERDAS IMAGINE Installation Guide.


  • When I print my map composition, the vector coverage is printed as thin black lines. Why is this happening?
    To correct this problem, you will need to save a symbology file for each coverage being displayed. Before you place your vector coverage in a map composition, use the Vector Viewing Properties dialog to define the way you want to display your vector coverage. Once you are satisfied with the changes, click on the Save As button on the bottom of the dialog. This will prompt you to define a file name and location for the specific display pattern to be saved and referenced from.


  • Why are tear lines created during the rubber sheeting process?

    In order to perform a geometric correction process using the rubber sheeting method it is necessary to use more ground control points than using for example, a polynomial transformation. The rubber sheeting model is a piecewise polynomial method for geometric correction. After a triangulated irregular network (TIN) is formed over all the control points, the image area covered by each triangle in the network is rectified by the first order (linear) or fifth order (nonlinear) polynomials. Whether or not to rectify the areas outside the convex hull of the TIN is determined by the preference under GCP Editor. It is not recommended to rectify the outside areas because of geometric uncertainty. Anything inside the convex hull is continuous. Anything outside is no longer a validly defined area. This model should only be used when:

    - the geometric distortion is severe
    - GCPs are abundant
    - no other geometric model is applicable

    However, if the user chooses to correct all of the image area (the preference ‘Rectify Outside Convex Hull of GCPs’ is enabled), but not enough GCPs are specified (ie. 1 GCP per image block), it is possible that so-called ""tear lines"" will appear, which look like the image is torn along a line. These tear lines are a function of point interpolation beyond the image extent. There are two ways to deal with the outside area if the user chooses to do so.

    1. Use a global function to interpolate the outside the convex hull of the image extent

    2. Collect GCPs along the edges of the imagery along with a large quantity of internal GCPs. Make sure that the preference setting ""Rectify Outside the Convex Hull of GCPs"" is not enabled (this preference is found in the GCP Editor category). This will triangulate with respect to the GCPs internally. This is a local transformation. However, this transformation will clip the image area outside of these GCPs collected along the edges.

    Depending on the distortion, the global function can create a disparity between the inside and outside. The way to minimize the problem (i.e., the tear lines) is to ignore the outside and to have points cover as much the input area as possible.


  • When I resample my imagery, the resulting image only contains data within the area bounded by my GCP points. How do I get the entire image to write to the output file?
    This is due to a GCP Editor preference setting. At the top of the main ERDAS IMAGINE menu, go to Session | Preferences and select GCP Editor from the category list. The last option in this category is Rectify Outside Convex Hull of GCPs. Select the checkbox adjacent to the option. Make certain to click User Save prior to exiting the Preference Editor.


  • Can I subset calibrated imagery?

    Yes, you can subset calibrated imagery to another calibrated image or to a geo-corrected image.

    To subset to a calibrated image

    • In the inquire box, select Type: File
    • In the subset dialog, select Coordinate Type: File

    To subset to a geo-corrected image

    • In the inquire box, select Type: Map
    • In the subset dialog, select Coordinate Type: Map


  • When mosaicking with many files the process slows down, yet it works fine when using only a few files. What causes this to happen and how can I fix it?
    Mosaicking files use a great deal of temporary space. This is because it is taking all of the images and performing calculations on the entire dataset in order to stitch the scenes together. This stitching processes is performed in the temp space. If your temp space is not large enough, the procedure will slow down when too many images are added. With fewer images, less space is needed and the process will run fine. Ensure you have enough temp space to accommodate an accumulation of all the files you wish to mosaic, plus additional space. The more space you have, the less fragmenting of your files is necessary.  We recommend that you have, at a minimum, 2.5 times the size of the input imagery available as free temp space.  You may specify the location of your temp space directory in the Preference Editor (Session | Preferences) under the User Interface and Session category.


  • When I perform a mosaic on multiple images, why does the brightness/color change dramatically?
    The color/brightness of the final mosaic image is sourced from one of the input image's lookup table (LUT) and is used for the entire mosaic. In other words, one LUT is used for the entire mosaic. This LUT defaults to the first image in the mosaic list dialog. The reference image column in the mosaic image list has an X in the Ref. column which denotes the use of the LUT from that specified image. Therefore, the mosaic will essentially look like the reference image with respect to brightness. You need to select the image which you believe best represents the color/brightness you would like to see across the mosaic scene. If problems still persist you may consider doing the mosaic in pieces, using different LUT’s across the image and then mosaicking those images together.


  • How do I change the projection information of my raster image?

    In order to change incorrect projection information:

    1. Display the image in a viewer.
    2. Open the Image Information by selecting the ImageInfo icon, , in the Viewer.
    3. In the Image Information dialog, go to Edit | Delete Projection.
    4. Confirm the deletion.
    5. Go to Edit | Change Map Model, and specify the correct projection and units.
    6. Confirm the projection change.
    7. Go to Edit | Add/Change Projection and specify the necessary parameters for the desired projection.
    8. Confirm the new projection change.

    Display the image again in a viewer and it should contain the correct projection information.

    Tip: If the Edit | Add/Change Projection option is used before steps 1 to 6 are carried out, the following error will occur:

    Projection names do not match! Projection name selected in Map Info is different.


  • In the mosaic tool, the images in my output have patches of very bright green and red that were not in the original image. What causes this?
    This is caused by zero values in one or more bands of the input images.

    By default, when running the mosaic the ‘Ignore Input Values’ is set to zero. If, however, you have very dark areas, such as trees or shadows, these ‘zero’ values are ignored in the process, and these ‘patches’ of very bright colors appear.

    To prevent this, you need to put a ‘null’ value in the ‘Ignore Input Value’ box. That is a value that does not appear in the images. For example, unsigned data can use the value to ignore of –999.


  • How do I determine the latitude/longitude boundary between UTM zones?
    UTM zones are 6 degrees wide, numbered sequentially moving eastward, starting at the International Date Line. If the longitude is exactly divisible by 6, it’s a UTM zone boundary. If you divide it by 6 and your decimal is exactly 0.5, it’s the midpoint in the UTM zone. For example, 24 degrees E or W divided by 6 is 4.0, so it is a zone boundary. 21 divided by 6 is 3.5, so it’s the midpoint of the zone (i.e., easting is 500,000).


  • Can I specify coordinates in degrees, minutes, and seconds in the GCP editor?

    It is possible to specify in the input and reference points in degrees, minutes and seconds within dialogs with the GCP Editor.

    For 12 degrees, 30 minutes, 48.11 seconds, specify in the CellArray:


    It will automatically change into decimal degrees as soon as you hit Enter. However, there is also a format option in ERDAS IMAGINE for these coordinates that can be found by accessing the hidden functions within dialogs such as the Coordinate Calculator as shown below. To access hidden functions, right-click in the column header.


  • For foot measurements, does ERDAS IMAGINE use the U.S. survey foot or the international foot?

    ERDAS IMAGINE uses the U.S. survey foot. Distance measurements are based on the conversion from meters.

    • U.S. survey foot = 0.3048006096012192 meters.

    See IMAGINE_HOME/units.dat for other available conversions.

    In 1959, the directors of the National Bureau of Standards and the United States Coast and Geodetic Survey agreed on a redefinition of the inch-centimeter relationship. This redefinition defined 1 inch as equal to 2.54 centimeters, exactly, or 1 foot as equal to 0.3048 meters, exactly. However, their agreement stipulated that the older value for 1 meter equaling 39.37 inches, exactly, be retained for identifying the U.S. survey foot. One of the reasons for this retention was that the State Plane Coordinate Systems, which are derived from the national geodetic control network, are based on the relationship of 1 meter equaling 39.37 inches, exactly. The difference between these two values for the foot is very small, two parts per million, which is hardly measurable but not trivial when computational consistency is desired. Fundamental survey units, such as rods, chains, statute miles, acres, sections, and townships, all depend on the relationship of 1 meter equaling 39.37 inches, exactly.


  • How do I fill the area under an AOI that is selected in the Viewer with a constant value?
    1. Ensure that the Vector layer that you are using is not displayed in the Viewer.
    2. Select the Build Topology option from the Vector menu.
    3. Display the Vector layer and click inside the desired vector polygon
    4. Select Vector | Viewing Properties and select the Polygon option.
    5. Save this layer.
    6. Create a new AOI layer under File | New | AOI layer. Make sure the Vector polygons you want to use are still selected and select AOI | Copy Selection to AOI.
    7. Save this AOI layer.
    8. This AOI layer can now be used in conjunction with the Raster | Fill option within the Viewer.


  • In the Mosaic tool, is there a way to histogram-match all three bands, rather than just one band, for two or more images?
    In the Mosaic tool, you can specify band-by-band or intensity matching. After the images are added to the mosaic tool, select Edit | Color Corrections | Use Histogram Matching and select Intensity (RGB) in the Histogram Matching dialog.


  • I want to change the resolution of a DEM, for example, from 30m to 15m, such that the four new 15m pixels will all have the value of the parent 30m pixel. How can I achieve this?
    1. In order to go from a 30-meter pixel to four 15-meter pixels, select Data Prep | Image Geometric Correction.
    2. Select an Affine model and use a linear adjustment of 2 for both the X and Y dimensions.
    3. Click Apply and then click on the Resample button from the Geo Correction Tools.
    4. Name your output file, use a nearest neighbor resampling method, and click OK.
    " "In the Mosaic tool, is there a way to histogram-match all three bands, rather than just one band, for two or more images?","

    In the Mosaic tool, you can specify band-by-band or intensity matching. After the images are added to the mosaic tool, select Edit | Color Corrections | Use Histogram Matching and select Intensity (RGB) in the Histogram Matching dialog.


  • What order of polynomial should I specify when resampling data in the geographic (latitude/longitude) coordinate system?
    Due to the non-linear nature of the latitude/longitude coordinate system, you should specify a 2nd order transformation for data of this type.


  • How can I specify a vertical datum in ERDAS IMAGINE?

    Prior to IMAGINE version 8.6, with the exception of the IMAGINE IFSAR DEM module, ERDAS IMAGINE did not support the assigning of vertical datums.

    IMAGINE 8.6+

    As 3D information becomes more and more important in GIS and LIS systems, correct handling of vertical datums becomes critical. If the reference point for a height or z value is unknown, then that coordinate is almost useless. ERDAS IMAGINE 8.6 therefore introduces the concept of vertical datum support for datasets with a height element, such as Digital Elevation Model (DEM) images, 3D coordinates, 3D Shapefiles etc. For example, without the correct information relating the vertical datum of a DEM to the vertical datum of 3D ground control (GCPs), the orthorectification process may introduce inaccuracies. The new tools in ERDAS IMAGINE enable you to define these relationships and transform data to a common vertical datum.


  • How does ERDAS IMAGINE treat null values in data?
    Null values are treated as zeros in ERDAS IMAGINE and LPS.


  • Is there a limit to the number of files that can be mosaicked in ERDAS IMAGINE?
    There is no specific limit in ERDAS IMAGINE as to how many files can be mosaicked. In most instances it is limited only by your operating system constraints.  It is recommended that you keep at least 2.5 times the combined file size of your input imagery as free temp space for the mosaic process.


  • What is the easiest way to combine vector, annotation and raster data into a single image?
    1. Once you have loaded all of the desired data into a Viewer, reset the zoom to a 1:1 ratio by clicking the Reset Zoom icon, , in the Viewer. This sets one screen pixel to the same resolution as one file pixel.
    2. Then simply select File | View to Image File. This creates a new IMG file with your vector and/or annotation data “burned” into the image.

    This images created with this technique are recommended for viewing purposes only. The output image should not be used for geographic analysis such as classification.


  • If I have a set of X and Y coordinates with a file value in an ASCII format, how do I get those into an ERDAS IMAGINE *.img file format?
    Use the ASCII Raster importer in the Import tools from the ERDAS IMAGINE main icon panel. The output file is, by default, a .img file.


  • Is there an easy way to transfer the color scheme from one thematic image to another?
    Copy and paste the Color column in the CellArray found in the Raster Attribute Editor. This procedure assumes that the class values for each image have the same meaning.


  • How can you append different AOI files together?
    Load the AOI files that you want to append into the same Viewer and use File | Save As to create a new AOI file.


  • How do I georeference NOAA AVHRR data?

    AVHRR images do not have a geographical extent, per se. Instead, each scan line contains a set of “Earth location” points (GCPs) at various intervals. These points can be used to perform a polynomial transformation, or calibration, of the image, but since the points are determined systematically by the satellite, they may not be as accurate as ground truth.

    Here are some suggestions that may improve your results with AVHRR georeferencing:

    • Perform panoramic distortion correction during import. This almost always reduces the RMSE of the polynomial transformation.

    • Extract the GCPs, rather than applying a calibration. This way, you have all of your geometric models (e.g., rubber sheeting) available to you, and you can examine the RMSE for various alternatives.

    • Look at the GCPs for any discontinuities. If your data is collected near the poles or the international dateline, you can get some very high RMSEs.

    • Consider converting your GCPs (using Coordinate Calculator) to your desired output projection before doing a geometric transformation. This is virtually a must if you have lat/lon discontinuities.


  • How can I open EO-1 HDF data in ERDAS IMAGINE 8.5 and later?
    EO-1 HDF data requires the Hyperion importer, standard in IMAGINE 8.6+. For IMAGINE 8.5, install Fix 15629 - IMAGINE Spectral Analysis Module, which adds the Hyperion importer.


  • How can I import a JPEG image with the associated JPEG World File (.jgw) in order to retain the geographic coordinates?

    Use the Import dialog to import the JPEG file to an .img file. Note the folder that the output file is being saved to. You must rename the extension of the .jgw file to .igw, and place this file in the same directory as the imported .img file. The .igw file is an ERDAS IMAGINE world file, and ERDAS IMAGINE will reference this file for the geographic information.

    In IMAGINE and LPS version 8.7, full support for the JPEG2000 file format, including GeoJP2, is standard.


  • I have data in an X-Y-Z format. How can I import this into ERDAS IMAGINE as a raster file?

    There are certain prerequisites to importing data using the ‘Convert ASCII to Pixels’ option from the Utilities menu on the main icon panel.

    The first is that it has a standard header section and secondly that the ‘spaces/gaps’ between the columns of data are ‘white spaces’ and not ‘tabs’.

    This example shows how to format the data using Microsoft Excel.

    To get the data into a ‘white space’ format, open the ASCII file in Microsoft Excel. Remove all superfluous information so that you are only left with the 3 data columns. Then save it to a PRN file format (this is a space delimited file format).

    Open the PRN file in Word Pad, and manually enter the header, so it looks like the example below.

    F1 : <directory listing>/<file name>.img


    X Y B1


    The file should then look like this:

    F1 : e:/tmp/ascii_100.img


    X Y B1

    0 0 9

    1 0 9

    2 0 9

    3 0 31

    4 0 31

    5 0 9

    6 0 9 etc.


    Then from the main icon panel, go to Utilities | Convert ASCII to Raster. Select the PRN file and run the program.


  • What information do I need to know to use the generic binary importer?

    In addition to the series of built-in importers and DLLs available in ERDAS IMAGINE, you may also import data using the generic binary importer. The generic binary importer requires that the user know certain information about how the data file(s) are stored. The information you need to know to use the generic binary importer will vary with the method of storage (BIL, BIP or BSQ) of the data. Information needed for importing this type of data can usually be found in a header file that accompanies the data file(s). Header information can either be located in a separate file or built into the file you are importing. This information can be viewed with the binary data viewer (Tools | View Binary Data), or click on the Data View button in the Import Dialog. Information you will need to know to use this importer successfully includes:

    • Data format: Either BIL, BIP or BSQ.
    • Data type: Number of bits per pixel (e.g., unsigned 8-bit, unsigned 16-bit).
    • File header bytes: This number will be reported if there is any header information before the image data in the file (this is usually the case when the image data is in a single file).
    • Image record length: This can be equal to the number of columns, but if a different number is reported, use that number.
    • Line header bytes: This is the number of bytes that precede the image data in each line. If line header bytes are present in a file, they will be reported.
    • Number of rows: The number of rows/lines in the image.
    • Number of columns: The number of columns/pixels in a row/line.
    • Number of bands: The number of image bands in the scene.


  • Is it advantageous to use IMAGINE Expert Classifier when classifying only one image with no ancillary data?
    The real utility of the IMAGINE Expert Classifier is its ability to use ancillary datasets and classification rules to better define a pixel class.


  • How can I assign the geocoding information in an image file after it has been imported using the generic binary importer?
    1. Use ImageInfo (Tools | Image Information) to assign geographic coordinates.
    2. Examine the header information of the file. Note the upper left coordinates, pixel spacing, units of measurement, projection system, spheroid and datum.
    3. Open a Viewer and display the image at the default zoom (i.e., do not select fit-to-frame or zoom in or zoom out)
    4. Open the Inquire Cursor utility.
    5. Align the inquire cursor with the upper left pixel of imagery. Look at the file location of the pixel. (i.e., pixel and line location)
    6. Calculate the number of pixels from the upper left corner of imagery to the upper left corner of the file (0,0). Use the information from the image header to calculate the upper left corner coordinates for the file.
    7. Open the ImageInfo dialog.
    8. Select Edit | Change Map Model.
    9. Enter the upper left file coordinates, the pixel spacing in the x and y directions, the units of measurement and the projection system. Click OK.
    10. Select Edit | Add/Change Projection…
    11. Under the Custom tab, use the available pull-down menus to add the parameters of the projection system. Click OK.
    12. Close the ImageInfo dialog.
    13. Redisplay the image for the changes to take effect.


  • My Hypothesis, Rules, and Conditions boxes are overlapping in the Decision Tree due to very long names or descriptions. Is there a way to define the size of these boxes?
    The size of the boxes are dynamically set to accommodate the text string which they contain, while the horizontal spacing of the boxes is fixed within the Decision Tree window. At this time changes can not be made to solve this problem


  • In the Knowledge Engineer, how do I delete a variable?

    This can be done in the Rule Properties dialog box. This can be opened either from the Knowledge Base Component List or from the Decision Tree.

    In the Knowledge Base Component List, select the Rules Tab. In the list of rules, select the rule for which the variable is the input. Then select the icon Show Properties of item on list.

    In the Decision Tree, select the rule for which the variable is an input. Then, to open the properties for that rule, right-click on the rule in the Decision Tree and select Properties.

    In the Rules Properties dialog box, highlight the row in the CellArray for the variable you wish to delete by clicking in the And column. Then, in the And column, right-click and select Delete Selection.

    Note: You need to be careful if you select a variable in the Decision Tree and then use cut, as deleting variables in this way will affect the rules and hypotheses.


  • How can on-the-fly reprojection be disabled?
    There is no way to disable on-the-fly reprojection in ERDAS IMAGINE and LPS. All images that appear in a single viewer must be of the same projection, and on-the-fly converts all follow-on images to the projection of the first image put in the Viewer. If this feature were disabled, you would have to manually reproject all the images you wanted to put in a single viewer. There can only be one projection in a Viewer. If you wish to view images of a different projection, you must open them in a separate Viewer.  In a single Geospatial Light Table, you may display up to four Viewers, each of which can have a different projection from the others, but the images in each Viewer are reprojected on the fly to match that of the first images opened in that Viewer.


  • How can I see the coordinates of points on a vector polyline displayed in a CellArray?
    Select the line within the coverage by left-clicking on the line. Then select the icon to ‘Reshape a single line by moving, adding or deleting vertices’. The line will now be selected with the polyline points visible. Now click-and-hold the left mouse button on the line, then select the space bar. A dialog box called Poly Edit will open displaying a CellArray of the line point coordinates.


  • How do I calculate statistics for an AOI?

    Select the AOI in the Viewer, then select the ImageInfo icon, , in the Viewer. This will open the Image Information dialog. Go to Edit | Compute Statistics. In the Compute Stats dialog, you have an option to calculate the stats only for the AOI. The new statistics for the AOI will be visible in the Image Information dialog.

    Tip: Make sure that the statistics are recomputed later again for the complete image, otherwise it will always show the statistics for the AOI only.


  • When using a magnifier in the Viewer, how do I change the color of the rotation box?

    Select the rotation box in the Viewer using the left mouse button, then press the space bar. This will open the RotBox Editor.

    If you have a rotation box open in the Viewer, the RotBox Editor dialog can also be opened by selecting Utility | Selector Properties… from the Viewer menu bar.

    To change the color, click and hold the color patch to select a color from a drop-down list. Selecting Other brings up the color wheel.

    This also applies to the rotation boxes which link to the magnifiers used in the GCP Tool.


  • Is there a limit to the number of ESRI arc coverage vector layers that can be displayed in the Viewer?
    There is no limit as to the number of arc coverages that you can display in the Viewer. However, you may only edit up to five coverages at one time.


  • In Windows, where can I change commonly used environmental variables in ERDAS IMAGINE?


    The HOME variable is set to the default home directory of the logged-in user. The default for this is “C:\Users\Default”. This variable is set in the ‘Profile’ dialog of the User Manager program. PERSONAL is then set to HOME\.imagine8XX. So these variables vary from one use to another and so are stored in the user's profile.

    In order to change the HOME variable, use the ‘Profile’ dialog of the User Manager program ( Start | Programs | Administrative Tools (Common)). If using an NT domain this would need to be set on the NT server. The PERSONAL environment variable will then be set to HOME\.imagine8XX.


    The temporary file directory for your machine can be changed through the system environments (Control Panel | System | Environment). This defaults to c:\temp.

    Within ERDAS IMAGINE, the temporary file location can be changed through Session | Preferences | User Interface & Session | Temporary file directory


    The IMAGINE_HOME environment variable is set to the location in which ERDAS IMAGINE was installed. This information is stored in the registry with the key ‘ImagineHome’. The environment variables listed in the ERDAS IMAGINE properties application are also stored in the registry with the key Environment. These variables are particular to ERDAS IMAGINE and not shared with any other program, hence, they are stored in the registry.

    (HKEY_LOCAL_MACHINE\SOFTWARE\ERDAS\IMAGINE\8X) The IMAGINE_HOME variable is set dynamically as the software starts and is set to the location in which the copy of ERDAS IMAGINE has been installed. So if ERDAS IMAGINE is installed into 'C:\Program Files\Imagine’ then that is what IMAGINE_HOME will be set to. If you change the name of the directory, e.g., ‘D:\Progs\Img’ then IMAGINE_HOME will be set to that next time ERDAS IMAGINE is started. The registry key is used for reinstalling and uninstalling ERDAS IMAGINE, add-on modules and fixes.


  • When running ERDAS IMAGINE from a client machine, it seems to take a long time to startup. Why does it take so long?

    This FAQ pertains to IMAGINE version 8.5 and earlier only.

    The client machine is accessing the ERDAS IMAGINE program files across a network from another machine. Each time a process or function is performed, the program files to perform that process or function must be accessed from the machine with the ERDAS IMAGINE files. Depending on the speed and traffic of the network, this process can be slow. Unless there are disk space limitations on the client machines, it is generally recommended that the full server/local installation be performed.


  • What bands are used during classification?
    By default, all bands are used when making a supervised classification. However, it is possible to select specific bands by using the Signature Editor and Edit | Layer Selection. Select the bands you want to use during classification.


  • What information do I need to know to use the generic binary importer?

    In addition to the series of built-in importers and DLLs available in ERDAS IMAGINE, you may also import data using the generic binary importer. The generic binary importer requires that the user know certain information about how the data file(s) are stored. The information you need to know to use the generic binary importer will vary with the method of storage (BIL, BIP or BSQ) of the data. Information needed for importing this type of data can usually be found in a header file that accompanies the data file(s). Header information can either be located in a separate file or built into the file you are importing. This information can be viewed with the binary data viewer (Tools | View Binary Data), or click on the Data View button in the Import Dialog. Information you will need to know to use this importer successfully includes:

    • Data format: Either BIL, BIP or BSQ.
    • Data type: Number of bits per pixel (e.g., unsigned 8-bit, unsigned 16-bit).
    • File header bytes: This number will be reported if there is any header information before the image data in the file (this is usually the case when the image data is in a single file).
    • Image record length: This can be equal to the number of columns, but if a different number is reported, use that number.
    • Line header bytes: This is the number of bytes that precede the image data in each line. If line header bytes are present in a file, they will be reported.
    • Number of rows: The number of rows/lines in the image.
    • Number of columns: The number of columns/pixels in a row/line.
    • Number of bands: The number of image bands in the scene


  • How many spectral bands can be present in an ERDAS IMAGINE image?
    There are no limits to the number of bands an ERDAS IMAGINE file can accommodate. ERDAS fully supports hyperspectral imagery, and a number of hyperspectral tools are available in IMAGINE Advantage under the HyperSpectral Tools menu. On the ERDAS IMAGINE main icon panel, go to Interpreter | HyperSpectral Tools.  In IMAGINE Professional, use the advanced Spectral Analysis tools under the Classifier icon.


  • Where are the ERDAS IMAGINE preferences saved?

    When you change any settings in a particular category, you must select User Save or Global Save.  User Save saves the preferences for the logged in user.  Global Save saves the preferences for all users.

    The preferences will be saved in the user's home directory under a directory called .v8preference.  In Windows, the user's home directory is typically C:\Documents and Settings\[your profile]\.imagine870.