This tutorial is designed to give you a working knowledge of ENVI's map composition capabilities. For additional information please see the ENVI User's Guide or the ENVI On-Line Help.
You must have the ENVI TUTORIALS & DATA CD-ROM mounted on your system to access the files used by this tutorial, or copy the files to your disk.
The files used in this tutorial are contained in the YS_TMSUB subdirectory of the ENVIDATA directory on the ENVI TUTORIALS & DATA CD-ROM.
The files listed below are required to run this exercise.
YSRATIO.IMG Yellowstone National Park TM Ratio Subset Image
YSRATIO.HDR ENVI Header for Above
YSRATIO.ANN Saved Annotation Result for Above
YSRATIO.GRD Saved Grid Parameters for Above
YS_LOC.GIF Location Image for Above
Map composition requires that the user be able to easily and quickly go from an image to an image-based map by interactively inserting the key map components. Map composition consists of defining the map extent; positioning the image within the extent using borders; adding pixel, map coordinate, and/or geographic (latitude/longitude) coordinate grids; constructing map keys, declination diagrams, and map scales; as well as placement of inset images and annotation.
Composing a map in ENVI is as simple as displaying the image, and then interactively adding the individual map components such as annotation, map scales, gridlines, etc. Templates of common map objects can be built and saved, and much of the placement of the objects used for map composition can be automated through the use of templates.
To begin, select the image for map composition, open the file, and load as a grayscale or RGB image into one of ENVI's display windows with the desired contrast stretch as indicated below.
Before attempting to start the program, ensure that ENVI is properly installed as described in the installation guide.
The ENVI Main Menu appears when the program has successfully loaded and executed.
To open an image file:
Note that on some platforms you must hold the left mouse button down to display the submenus from the Main Menu.
An Enter Input Data File file selection dialog appears.
The Available Bands List dialog will appear on your screen. This list allows you to select spectral bands for display and processing.
Note that you have the choice of loading either a grayscale or an RGB color image.
The bands you have chosen are displayed in the appropriate fields in the center of the dialog.
Click "Load RGB" to load the image into a new display.
Once the image is displayed, follow the steps below for individual components and the sequence of map composition.
Figure 1: Yellowstone National Park Landsat TM Color Ratio Composite image. Ratios 5/7, 3/1, and 3/4 as RGB.
The ENVI Main Display window, Scroll window, and/or Zoom window are used to perform map composition.
Figure 2: ENVI Map Composition Layout Screen in the Scroll Window.
Default ENVI displays contain only the image, with no surrounding blank space. Map composition typically requires that some map objects reside outside the image proper. ENVI provides a "Virtual Border" capability that allows annotation in the image borders without creating a new image. Virtual borders can be added to an image in several ways.
A virtual border will be added to accommodate the grid. See the specific grid instructions below for information on setting up the grid. A 100-pixel border is automatically added on all sides of the image.
The new virtual border characteristics will be applied immediately to the image. If you save the Grid Parameter File, the border information will be saved with the grid and will be restored when the grid parameters file is restored.
The Set Display Borders dialog will appear with the number of border pixels listed in text boxes that correspond to image geometry. This dialog is also used in Grids and Annotation to set the virtual border size.
The top text box controls the top border, the right text box the right border, the bottom text box the bottom border, and the left text box the left border.
The next image displayed using the Available Bands List will be displayed with the borders applied.
The Display Parameters dialog will appear, containing text boxes similar to those described above.
The new borders will be applied to the image immediately.
The new virtual border characteristics will be applied immediately to the image. If you save the Annotation File, the border information will be saved with the annotation and will be restored when the annotation file is restored.
ENVI supports simultaneous pixel, map coordinate, and geographic (latitude/longitude) grids. A 100-pixel virtual border (which can be adjusted as described above) is automatically appended to the image to accommodate the grid labels when Grids are applied. To add grids to an image:
The Grid Line Parameters dialog will appear with default grid spacings set.
This allows editing of the line and label characteristics for the grid.
To save Grid parameters for later use, select File->Save Setup from the Grid Parameters menu bar and select an output file.
This saves a template of the grid parameters, which can be recalled for use on another map composition by choosing File ->Restore Setup from the Grid Parameters menu bar.
Annotation is used as a generalized means of inserting map objects into an ENVI display for map composition. Several classes of map objects are available and all are placed using ENVI's standardized annotation procedures.
The various types of annotation available in ENVI are discussed below. Please see the ENVI User's Guide or the ENVI On-Line Help for more details.
ENVI currently has 14 standard text fonts and 3 different standard symbol sets. In addition, ENVI can utilize TrueType fonts installed on your system. This provides access to a wide range of different text fonts and symbols. All of these can be interactively scaled and rotated, and different colors and thickness can be set.
Figure 6: ENVI Text Annotation
TrueType fonts provides more flexibility. Select one of the available Truetype fonts available on your system by choosing TrueType from the pulldown Font menu and selecting the desired font. Enter the character you want and place using the methods described above.
ENVI allows you to draw rectangles, squares, ellipses, circles, and free-form polygons. These can be an outline only, or filled with a solid color or a pattern. Placement is interactive, with easy rotation and scaling.
ENVI annotation allows the placement of polylines (lines) and arrows. You have full control over the color, thickness and linetype, and the fill and head characteristics for arrows.
Map Scales are automatically generated by ENVI based on the pixel size of the image being used in the map composition. Options include feet, miles, meters, and kilometers. Scales can be placed individually, or in groups. The number of divisions and minor divisions is completely configurable, as is the font and the character size.
ENVI automatically generates declination diagrams based on user-provided characteristics. The size of the diagram and the azimuths for True North, Grid North, and Magnetic North are entered in decimal degrees and the diagram is placed using standard ENVI annotation procedure.
Shown below is an example of a map key build using ENVI's map key editing facility. The box around the key is a rectangle placed as a separate annotation object as is the key description at the top of the box.
Map keys are generated automatically for classification images and vector layers.
You can create grayscale ramps and color bars for grayscale and color-coded images respectively. This option is not available when an RGB image is displayed.
While many images are inset into other image using ENVI's mosaicking capabilities, ENVI annotation provides the capability to inset images into other images during the map composition/annotation process as well.
Because 8-bit displays can not easily assign a new color table to the inset image, ENVI only shows a representation of the image in the display window. The actual image is placed when the image is output to a file and the annotation is burnt in.
ENVI can import ArcShape, Arc/Info Interchange, DXF, and DLG vector formats. Vectors from these files and internal ENVI Vector Files (.evf) can be used in an ENVI map composition.
The image-map composition can be output from the Main Display window.
Options include Postscript, ENVI (binary) image, BMP, GIF, HDF, JPEG, PICT, SRF, TIFF, and XWD, as well as common image processing system formats such as PCI, ERDAS, ERMAPPER, and ArcView Raster.
You can also select direct printing, in which case, the map composition will be printed directly to your hardware using system software drivers.
In all of the above cases, graphics and map composition objects will be burned into the image on output.
The figure below shows an example of a finsl map composition produced in ENVI.