You can use the Scatter Plot window to show elliptical graphs for all training sites. A class ellipse shows the maximum likelihood equiprobability contour defined by the class threshold value entered for the mean.
Threshold: is a relative measure used to control the radius of the hyperellipse for each class. By changing the threshold values, you can reduce the chances of pixels being classified into more than one class.
Bias: is a value from 0 to one, where higher values weigh one class in favor of another. It can also be used to resolve overlap between classes. You can use both of these measurements to test the training site separability.
Ellipses cannot be plotted for invalid signatures. Invalid signatures represent training sites with the total number of pixels below the required minimum (the number of selected channels), or with a numerically singular (zero or negative determinant) covariance matrix.
Correct invalid signatures, either by collecting additional training pixels, or by merging them with other signatures.
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