[GRASS-user] improve v.rast.stats speed?

[Markus Metz]

Markus Metz wrote:
>
> G. Allegri wrote:
>> Hello list.
>> Yesterday I needed to use v.rast.stats on a 1793 areas covering a
>> 4415x6632 raster (with resolution 50m/pixel). I've used it without
>> extended statistics but the processing time was, with an euphemism,
>> very very long. After 5 hours it wasn't finished yet. As I needed it
>> for today morning I've decided to reproduce it with ArcGIS: 40
>> seconds. I've tried to investigate what was going wrong, the
>> bottleneck, but at the end I suppose that it's a problem of the script
>> itself (the looping chain of r.mapcalc and r.univar, the creation and
>> deletion of the MASK in each loop).
>> Is there any way to improve the performance of v.rast.stats? Should we
>> rewrite it in C and avoid the use of MASKs?
>>   
> I have two ideas.
> 1) Use r.reclass instead of r.mapcalc to create new masks. That should 
> speed up at least the MASK creation and deletion
> 2) Avoid the loop and MASK creation altogether. Run r.univar 
> map=tmpname,raster. Process the output of r.univar, separate stats for 
> the different vector areas and convert to sql statements. Proceed as 
> before. r.univar would be called only once. I'm not sure if this is 
> possible. I also don't know if the speed gain by avoiding the loop is 
> annihilated by r.univar having to process two rasters as input.
>
Idea 2 is nonsense, I hoped for some behaviour like in r.statistics.