Conditional operator in RasterCalc
03.02.2011 19:24 · GIS · qgis, plugins, rastercalc
Despite the fact that QGIS now has a built-in raster calculator (I wrote about this a couple of times), the RasterCalc plugin I developed is still quite popular. I don’t know how to explain it: either it’s a matter of habit, or my calculator is more convenient… I’d like to know what the reason is, maybe I should make a poll.
Why this preface? For a long time, I’ve been “terrorised” by requests to add support for conditional operators to my plugin. A guy from Spain was particularly active. And no matter how often I pointed out that I was busy with other projects, no matter how hard I tried to avoid it, nothing helped. After a short break, the “attacks” were repeated. Apparently, they had decided to wear me down.
The inclusion of a patch that added comparison operators (submitted by Ghislain Picard) didn’t help either. It was not enough, and it was not what they were looking for. People wanted more, something similar to r.mapcalc from GRASS and preferably with the same syntax.
Well… I have to admit, they got it. Today this most wanted feature is implemented. However, the syntax is different from r.Mapcalc’s, because I didn’t want to make the already complex parsing code even more complicated. Now you can do things like:
- compare pixel values with a constant and replace pixel values that meet the condition with another value
- compare pixel values with corresponding pixels of another raster/band, and replace pixel values that match the condition with corresponding values from the third raster/band
- other similar things
This nice feature is still in my local repository. I will not commit it to the public repository until the documentation has been updated. And I really don’t have the mood or energy to do that. I don’t like writing, whether it’s an essay, an article, or anything else. There are times when it is easy to write, but those are rare.
There is another reason or two, to be precise and honest. Firstly, I’m thinking about optimising the plugin a bit: operations on large rasters use a lot of CPU and memory. And secondly, that very active Spaniard made another feature request the other day, and I have a feeling that he will be as persistent in his efforts to get me to implement it as he was before.
But I haven’t made a final decision yet. Maybe the conditional operator should be enough for a new version and I should not bother with refactoring and optimisation? Or should I wait a bit, but release an even more powerful calculator and consolidate the success of the first versions?