Q: Comparing two rasters, based on a complex set of rules.
I am trying to compare two rasters, say A.tif and B.tif. Both correspond to river bed level changes under two different flow conditions. Now I want to produce a comparison raster having values based on certain rules. The rules for the value of pixel are following:
| Pixel Value | Rule |
|---|---|
| 0 | Both A and B does not cause any significant bed level change (less than 10% of Min (Range_A, Range_B) |
| 1 | Both A and B are positive and are equal (the difference is less than 10% of Min(Range_A, Range_B) |
| 2 | Both A and B are negative and are equal (difference less than 10% of Min (Range_A, Range_B) |
| 3 | A is positive and B is negative (A > 0 and B < 0) |
| 4 | A is negative and B is positive (A < 0 and B > 0) |
| 5 | Both A and B are positive. Positive change due to A is more than that of B (i.e., A > B) |
| 6 | Both A and B are positive. Positive change due to B is more than that of A (i.e., A < B) |
| 7 | Both A and B are negative. Negative change due to A is more than that of B (i.e., A < B) |
| 8 | Both A and B are negative. Negative change due to B is more than that of A (i.e., A > B) |
The raster calculator in the current version of QGIS (3.22.2) supports conditional `if` statements. Although, it is possible to do it in the raster calculator using a complex and lengthy expression. Probably by looping many `if` statements in each other. The problem with using Raster Calculator is that it cannot programmatically get the `range` of a certain raster. …
A little R-script named mk-class-river-bed.R was written, to
demonstrate the basic steps of raster calculation for the two spatial
synchronous incoming rasters A.tif and B.tif. The script handles:
- get data informations and load the GeoTiff files using
rgadal, - Conversation of the GDAL objects to a plain R raster and subsequent raster calculations,
- classification schema for the resulting raster,
- back-substitution of the result to a GeoTiff,
- display of the result and storage.
- (C) 2021 A. Weidauer <alex.weidauer@huckfinn.de> 2021
- and is licensed by the 3-clause BSD license