[Qgis-developer] raster algebra plugin II - the return!
Kolberg Sjur A
Sjur.A.Kolberg at sintef.no
Fri Nov 28 16:45:41 EST 2008
If you're taking votes...
My suggestion would be a multi-line edit window for the expression, where raster bands could be written as variable names. Much quicker than loading files for each raster (if you remember the names), some insert-image button could allow browsing.
I haven't really got started using Qgis, but a couple of annoyances in my current GIS software is 1: The map calculator doesn't honour flag values, but pushes the 0, -9999 or whatever directly into the calculations. 2: The use of numerical constants is very restricted, many operators only accept either rasters or scalars on both sides. 3: After breaking the total expression down to elementary operations - each operation is handled by an overlay macro. Meaning, up to n-1 maps are stored to and re-read from disk before the calculation finishes.
A good map calculator is highly valuable, I really appreciate your work.
Sjur K :-)
SINTEF Energy Research
From: qgis-developer-bounces at lists.osgeo.org [mailto:qgis-developer-bounces at lists.osgeo.org] On Behalf Of Barry Rowlingson
Sent: Friday, November 28, 2008 8:54 PM
Subject: [Qgis-developer] raster algebra plugin II - the return!
my old raster algebra plugin was a bit creaky and limited in its functionality. I think it was the second plugin I wrote and it shows.
So after someone emailed me to say they were actually using it, I figured I should put some time into its successor.
What I'm doing is writing a parser for a mini-language for raster processing. So you can write something like:
(max(R1)-min(R1)) * sqrt(R1*R1 + R2*R2)
and get a new raster with the computed values in.
R1 and R2 (and R3 up to Rn) will be raster bands (old rasteralgebra only liked single-band rasters) and the range of available functions and operators will be taken from things that python's numpy module provides for array operations (and that make sense as geo-rasters).
For the gui I think I'll have some way of defining raster bands as R1 to Rn, and then an input line for the expression and a file to save the result. As before, all rasters will need to be the same size and spatial location.
Anyone got any suggestions/requests for this?
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