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Exercise 3.

Subset and Mosaic

by: Miles Logsdon

There are multiple ways to clip (SUBSET) an image, many of them use the subset command. The method that I have used and found to work the fastest is the following: . 

1. Open ERDAS IMAGINE from your desktop by going to Start --> Programs --> ERDAS IMAGINE 

2.  In the Viewer window go to File --> Open --> Raster Layer.....   and find the bbcgis folder.  Open the "pnw98_bbg.img" file from the folder. 


4. Move the box and enlarge it to include the area you want to clip

5. Click the DATAPREP button, and select SUBSET IMAGE

6. Fill out the options selecting the image input and output, and click on FROM INQUIRE BOX button. This will make a .img file that contains the area, layers, and data type you selected.

REPEAT those steps until you have the subsets you wish to work with.

NOW here is one method to (MOSAIC) multiple Images (individual blocks) together. Once you have all your clipped images, you will want to put them back together for your unsupervised classification. Do the following:

1. Click the DATA PREP button, and select MOSAIC IMAGE

2. Click EDIT and ADD IMAGE or use the button . Add all your clipped images

3. Then click PROCESS and RUN MOSAIC

4. This will make a new .img file with all your clipped images included.

5. You'll need to contrast stretch the resulting image. Raster --> Contrast --> General Contrast. Try the linear option.

You can play with the contrast to make the visual that you like.

IMPORTANT:  When you close ERDAS, you will be asked if you want to print the Log File.  Say NO.