ERDAS Imagine Icon Panel (above).
ERDAS Imagine Image Subsetting
There are two satellite images of the area around Acadia National Park in Maine. One image was taken May 19, 2000(Landsat 7), the second on September 10, 1989 (SPOT). These images are quite large. You will take a subset of the images to narrow in on our area of interest and to decrease processing times.
Make a directory in U:maine00 called mdi.
Subsetting an Image
Start ERDAS Imagine version 8.5: Start --- Programs --- ERDAS IMAGINE 8.5 --- ERDAS IMAGINE 8.5
An icon panel will appear with 13 buttons, Viewer, Import, DataPrep, etc.
A Viewer window will also appear. This is where the software will display a digital image.
In the Viewer window there is a Menu Bar with 9 dialog box headings; file, utility, view, etc. The Tool Bar is just below the Menu Bar and contains many icons.
Left-click on file and an icon menu appears. Left-click on open and then left-click on raster. A raster icon menu will appear. You will be displaying a raster SPOT image of the Mt. Desert Island, Maine area. The image file is 081486.img. Navigate to /scratch/maine00/mdi to read in the image.
Make a subset of the original image with the following borders;
Northeast Corner - include Bar Island, Sheep Porcupine Island and Bald Porcupine Island.
Southeast Corner - include Greening Island, Sutton Island, Bunker Head on Little Cranberry Island, all of Somes Sound and southern tip of Echo Lake.
Make sure Great Head is included in the in the east-central portion of the image.
Use the maps on the wall of room 1090B to find geograpic features.
To make a subset of an image, you resize an inquire box to include the area you want. In your active viewer left-click on Utility --- Inquire Box. A small rectangular box appears in the image and a dialog box appears that contains the map or file coordinates of the Inquire Box.
In the Inquire Box dialog box choose Type: File. Left-hold the mouse button and you can move the box and resize it by dragging depending upon where in the box you put the cursor. The inquire box defines a region. To Subset that region, go to the Icon Panel, left-click on Interpreter --- Utilities --- Subset. The Subset dialog box appears. You have to specify an input and output file. The input file will be the same file you are viewing and have the inquire box defining an area of interest (AOI). The output file will go in the directory you created in your home directory. Make the output filename descriptive taking into consideration you may have many different files in this directory.
In the Subset dialog box choose Coordinate Type: File and choose From Inquire Box. This means that the XY coordinates for the subset will be from file coordinates derived from the inquire box active in the viewer. Notice the XY coordinates in the Subset dialog box are the same as those in the Viewer inquire dialog box. A Modeler dialog box will appear in the upper-left corner of your screen indicating job status. When it is 100% done you can dismiss the dialog box.
Now open this new image in Viewer #1.
Repeat the Subset procedure for the 091089.img image.
Once you complete the procedure on the second image, display them side-by-side by left-clicking on the Session heading and then Tile Viewers. The two viewers will contain the same view of two different dates to be compared.