Subsetting an image
A typical Landsat scene covers an area of about 185km by 185km. At times, it makes sense to cut out a subset of this larger image to simplify analysis and focus on the portion of the scene that is of primary interest. By working with data that has a smaller file size it allows faster processing and display updates.
Creating an AOI layer
These options allow to define an AOI (Area of Interest) in the image, excluding other parts of the image. Specific processes can be applied to this AOI only, which can save considerable time and disk space. The option to use a specified AOI for processing is available from many dialogs throughout ERDAS IMAGINE.
The exercise is about how to create an AOI layer that can be saved as a file and recalled for later use.
_ NOTE: Each viewer can display only one AOI layer at a time._
Select File → New → 2D View → AOI layer from the viewer menu bar. Open AOI Tools
-
Select Drawing button from the viewer menu bar.
-
Click the Rectangle icon from insert geometry in the AOI tool palette.
-
Move the cursor into the viewer window.
-
Drag and the release to draw a rectangle over the AOI. Save AOI
-
Select File → Save → AOI layer as from the viewer menu bar.
-
Enter the name for the AOI layer under save AOI as (the AOI extension is added automatically).
Steps
-
Create an AOI layer that we want to subset out.
-
Select Raster → Subset and chip → Create subset image .
-
From the Subset dialog box, select the input file and anoutput destination and file name also add the AOI layer.
-
When the job is done, push the OK button and your subset is ready to go.
Satellite image obtained from USGS is shown above and subset image is shown below
