<p>Task: compare the Mahalanobis distance from different region.</p> <p>I made two raster datasets: 1) grassland from region A and grassland from region B; 2) grassland from&nbsp;region A and grassland from&nbsp;region C.</p> <p>Then:</p> <p>&gt; created ROI using all pixels (e.g. roi_A1 means all grassland pixels located region A in dataset 1;roi_A2 means all grassland pixels located region A in dataset 2)</p> <p>&gt;&nbsp;Mahalanobis distance classification was used for the two datasets seperately based on the above ROI</p> <p>&gt;Average of "rule image" was calculated within each ROIs.</p> <p>Now the problem is the average distance from region A are inconsistent from two datasets.</p> <p>Could anyone explain why? Thanks</p> <p>(ENVI version 5.2)</p>