When you have the Table of Contents open along with the Image Analysis Window, you’ll notice that the order is the same in both. Move an image up in the TOC and it will move up in the Image Analysis Window too. This ordering is very important to be aware of when using tools in the Processing Pane that require you to select two or more layers. What it does is assume that the layer that is higher in the TOC is the first input, and the lower one is the second input. For example, if you are calculating the difference between two images, the image that is lower in the TOC is subtracted from the image that is higher within the TOC. This logic also applies to other processes as well: Composite Bands, NDVI, and Mosaic.
Next week we’ll show you how to use the logic behind layer ordering in the Image Analysis Window with the NDVI tool to create other indices.
Written by Kevin J Butler