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ENVI

Examine SAM Results

Examine SAM Results

The Investigate SAM Results panel represents step 6 in the workflow. Here, you can display and examine the results of the SAM analysis.

The output from SAM is a classified image and a set of rule images corresponding to the spectral angle calculated between each pixel and each target (one rule image per target).

  1. Click Load SAM Class Result to examine the SAM classification image. If the image does not show spatially coherent classes, then the classification does not match the target spectra or what you know about the target. In this case, you should review the SAM rule images.
  2. Highlight the name of an image in the SAM Rule Images list and click Load SAM Rule Image, or double-click the image name in the SAM Rule Images list.

    The rule image is loaded into a display group using an inverted color table. (The ENVI Color Tables dialog also appears.) A smaller SAM angle means a pixel is a better match to the target. Inverting the color table displays the best matches as brighter pixels, which is more intuitive.

    A histogram of the image also appears in a separate interactive stretching dialog. This histogram explicitly shows the linear stretch applied to the display of the rule image. A flat line in the left portion (lowest value) of the histogram indicates a good separation of targets and backgrounds. Any data values to the left of this flat line are significant matches for the target spectra.

  3. The display group is linearly stretched to a maximum value specified by the Default Stretch Max value in the SAM Rule Images section of the Wizard. The initial value is 0.10. To change the default stretch maximum when you display rule images, enter the desired Default Stretch Max value is less than the minimum value in the rule image band, the minimum value will be used instead.
  4. Double-click in the display group to open the Cursor Location/Value tool. Evaluate the SAM spectral angles for each pixel.
  5. You can increase the maximum angle threshold to make the classification more relaxed, or decrease it to make the classification more selective. Click Prev in the Wizard and enter a new SAM Maximum Angle value if desired.
  6. Click Show Report to view the results of the SAM Target Finder with BandMax Wizard. The SAM is not recalculated if you clicked Prev to get back to this step.
  7. If you are satisfied with the results, click Finish to exit the Wizard.
  8. If you are not satisfied with the results, you can refine your targets, backgrounds, or both. To return to step 2 of the Wizard workflow and repeat these steps, click Next.



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