[GRASS-user] speeding up context evaluation...

[Maris Nartiss]

Sorry, I was not reading carefully Your code snippet, but can't You
just use mapcalc's ability to access neighborhood pixel values (see
"THE NEIGHBORHOOD MODIFIER" in help page). Like
output=if(location[-1,-1],validation,null()) || etc...
It may eliminate need to create buffer, mask etc. still if it takes
lot of time, consider to create new C module. Also take a look at
v.sample.

Maris.


2008/12/2, Hufkens Koen <koen.hufkens at ua.ac.be>:
>
> Hi list,
>
> for a validation exercise I need to extract the class values around certain
> pixel location.
>
> I have a map with all the locations (numbered) and a map with the validation
> map.
>
> The code you find below is the one I came up with to get this information
> (only output to terminal for the moment).
>
> However, this code includes a loop and is terribly slow. Has anyone an idea
> how to speed things up?
>
> Kind regards,
> Koen
>
> ---------- my code -------------
>
> #!/bin/bash
> #
> ###########################################################################################################################
> #
> # Get context around pixels...
> #
> # !!! Bash script only works within the GRASS terminal !!!
> #
> ###########################################################################################################################
>
>
> #
> # get number of pixels in location file... write to variable $pixels...
> #
>
> pixels=`r.info -r map=$1 | tail -n +2 | sed 's/max=//'`
>
> echo "their are $pixels groundtruth points..."
>
> for i in `seq 1 $pixels`;
> do
>
> echo "evaluating pixel $i of $pixels pixels..."
>
> #
> # Make MASK based upon pixel number evaluate one at a time. Mask name is
> MASK and patch.mask
> # after renaming... If kept as MASK it will apply to all operations and is a
> system wide setting (not wanted)...
> #
>
> r.mask -o input=$1 maskcats=$i --quiet
> g.rename rast=MASK,pixel.mask --overwrite --quiet
>
> #
> # create buffer around pixel value...
> #
>
> r.buffer input=pixel.mask output=tmp.buffer distances=4 units=meters
> --overwrite --quiet
>
> #
> # writes temporary reclass rules file...
> #
>
> echo "1 = NULL" > tmp.rules
> echo "2 = 1" >> tmp.rules
> echo "end" >> tmp.rules
>
> #
> # reclass context values using rules above...
> #
>
> r.reclass input=tmp.buffer output=context.mask rules=tmp.rules --overwrite
>
> #
> # calculate category statistics for pixel and context location...
> #
>
> r.mapcalculator amap=pixel.mask bmap=$2 formula=A*B outfile=pixel.category
> help=- --overwrite --quiet
> echo "pixel data..."
> r.stats -c -n input=pixel.category fs=space nv=* nsteps=255
>
> r.mapcalculator amap=context.mask bmap=$2 formula=A*B
> outfile=context.category help=- --overwrite --quiet
> echo "context data..."
> r.stats -c -n input=context.category fs=space nv=* nsteps=255
>
> done
>
> #
> # clean up tmp files...
> #
>
> rm tmp.rules
> g.remove rast=pixel.mask
> g.remove rast=context.mask
>
> echo "!!!DONE!!!"
> echo
> "#########################################################################"
>