Plot Digitizer is a Java program used to digitize scanned plots of functional data. Often data is found presented in reports and references as functional X-Y type scatter or line plots. In order to use this data, it must somehow be digitized. This program will allow you to take a scanned image of a plot (in GIF, JPEG, or PNG format) and quickly digitize values off the plot just by clicking the mouse on each data point. The numbers can then be saved to a text file and used where ever you need them. Plot Digitizer works with both linear and logarithmic axis scales. Besides digitizing points off of data plots, this program can be used to digitize other types of scanned data (such as scaled drawings or orthographic photos).
Plot Digitizer includes a special "semi-auto" digitizing feature. For plotted data that trends from left to right, you can simply indicate what data you want digitized with a thick paint brush and the program will automatically sort out grid lines, noise, etc, and will attempt to digitize the line for you. This feat is accomplished with the help of the open source autotrace image vectorization program.
Will the auto-digitizing feature digitize any plot? Short answer: no. Long answer: The auto-digitizing feature works best with black and white, 300 dpi images of continuous data which does not run vertically (vertical lines give it fits), does not repeatedly cross other data lines, is not close to and parallel to grid lines, is not extremely noisy and which does not have plot symbols. After using the program a while you begin to learn what it can and can't auto-digitize. However, even in cases where it doesn't auto-digitize the entire line, you can sometimes do a piece of it automatically, then manually digitize a piece, and then do another piece automatically, etc. I've found this feature to be pretty useful on digitizing plots of experimental test time histories, but your mileage may vary.
To make the digitizing task easier, this program includes many handy features. For example: You can recalibrate the Y axis without having to recalibrate the X axis (multiple sets of data are commonly plotted with the same X axis). You can insert points between two already digitized points by right clicking and choosing "Insert" from the pop-up menu. You can delete points by right-clicking on the points and choosing "Delete". You can move points by clicking and dragging them. You can calculate the length of a digitized line and the area enclosed by a digitized polygon of nearly arbitrary shape. Finally, there is also unlimited undo/redo.
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
First go to the downloads area and download the appropriate executable version of the program for your platform, and/or it's full source code, from there.
You should have received this application as a compressed disk image file (PlotDigitizer_#.#.#_MacOSX.dmg). This disk image file, when mounted (by double-clicking on it), should contain the application icon (Plot Digitizer.app, a readme file (README.txt), and some license related legalese.
To install this program, simply drag the Plot Digitizer.app icon to a convenient location on your hard drive. In MacOS X this is usually the "Applications" directory, but you are free to put it anywhere you want.
The application file should work properly on MacOS X 10.5 or later right out of the box. No additional software required.
If you want to use the auto-digitize feature, you must acquire and install the autotrace program separately. Also, the autotrace program must appear on the System search path. I recommend you use either the Fink (http://www.finkproject.org/) or MacPorts (http://www.macports.org/) package managers to install autotrace. Plot Digitizer will find autotrace automatically if one of those package managers are used. Otherwise, if you install autotrace from source or from a binary distribution, make sure the executable is found in /usr/local/bin or /usr/bin.
You will first have to make sure that you have the J2SE 1.5 or later installed on your computer. If you do not, you can get it from: http://java.sun.com
You should have received this application as a ZIP archive file (PlotDigitizer_#.#.#_Windows.zip). Uncompress this archive (with WinZip). It contains an executable file named PlotDigitizer.exe, a readme file (README.txt), and some license related legalese.
To install this program, simply drag the PlotDigitizer.exe icon to a convenient location on your hard drive. It should work from anywhere.
If you want to use the auto-digitize feature, you must acquire and install the autotrace program separately. Also, the autotrace program must appear on the user's search path. After installing or building autotrace, add it to the search path. To do this, from the "Start" menu choose "Settings" and then "Control Panel" and from the Control Panel window double-click on "System." Then click on the "Advanced" tab and then the "Environment Variables" button. Under "User variables" if the PATH variable is listed, then select the PATH variable and click on the "Edit" button. Enter the path to the directory containing the autotrace executable (path items are separated by semi-colon (";") characters). Otherwise, click on the "New" button, enter "PATH" for the variable name and enter the path to the directory containing autotrace for the variable value.
Linux (and many flavors of UNIX):
You will first have to make sure that you have the J2SE 1.5 or later installed on your computer and on your search path. If you do not, you can get it from: http://java.sun.com
You should have received this application as a compressed archive file (PlotDigitizer_#.#.#_Linux.tgz). After decompressing this file using "tar -xvzf PlotDigitizer_#.#.#_Linux.tgz", you will get a file named PlotDigitizer.jar. This is a "double-clickable" jar file, or you can run it from the command line using:
java -Xmx128m -jar PlotDigitizer.jar
You may want to create a shell script to do this for you.
If you want to use the auto-digitize feature, you must acquire and install the autotrace program separately. Also, the autotrace program must appear on the user's search path.
Quick Instructions: To use this program, first scan a plot with your favorite scanning system, then save the plot as a GIF, PNG, or JPEG format file. Run Plot Digitizer, open the scanned image file from the "Open" command in the "File" menu. Then follow the instructions at the bottom of the window to calibrate the plot and then digitize the points.
If you want to compute the length of a digitized line or the area enclosed by a digitized polygon, then you will need to pick those options from the Analysis menu before clicking on the "Done" button.
Hint: If you want to digitize plots from published technical reports that are available electronically in PDF format, you can skip the "print and then scan" step and keep everything digital. On Windows you can use Acrobat Reader and on MacOS X you can use Preview to select a rectangular area and copy it to the clipboard (at screen resolution, so zoom in first). Then use a graphics program to paste in the image and save it to a GIF or PNG file. Then you can use that file with Plot Digitizer. Under Linux, you can use the PDF Toolkit to extract the page you want and then use ImageMagic to convert it to GIF or PNG at any resolution you want. Then you can use the file with Plot Digitizer.