Image change detection

Change detection allows you to automatically highlight the differences between two images in the same area if they are properly orthorectified. In this recipe, we'll do a simple difference change detection on two images, which are several years apart, to see the differences in urban development and the natural environment.

Getting ready

You can download the two images for this recipe from https://github.com/GeospatialPython/qgis/blob/gh-pages/change-detection.zip?raw=true and put them in a directory named change-detection in the rasters directory of your qgis_data directory. Note that the file is 55 megabytes, so it may take several minutes to download.

How to do it...

We'll use the QGIS raster calculator to subtract the images in order to get the difference, which will highlight significant changes. We'll also add a color ramp shader to the output in order to visualize the changes. To do this, we need to perform the following steps:

1. First, we need to import...