[GRASS-dev] Creating / reading in random sample of raster values in Python script

[Paulo van Breugel]

On 25-03-17 23:11, Laurent C. wrote:
> Hello,
>
> If you need a fixed number of points, you might do a while loop that 
> randomly generate coordinates then add the point only if the array is 
> not null at those coordinates.

Thanks, I'll give that a try. Will also see how this compares with using 
r.random/r.what in terms of speed.

>
> Laurent
>
> On 25 Mar 2017 13:55, "Paulo van Breugel" <p.vanbreugel at gmail.com 
> <mailto:p.vanbreugel at gmail.com>> wrote:
>
>     On 25 March 2017 20:21:18 Luca Delucchi <lucadeluge at gmail.com
>     <mailto:lucadeluge at gmail.com>> wrote:
>
>     > Il 25/mar/2017 20:07, "Paulo van Breugel"
>     <p.vanbreugel at gmail.com <mailto:p.vanbreugel at gmail.com>> ha
>     > scritto:
>     >
>     > Hi,
>     >
>     >
>     > Hi,
>     >
>     >
>     > For a script I am working on, I am looking for a way to select a
>     X number
>     > of raster cells and their values into a numpy array. I can
>     create a layer
>     > with r.random, and read in that layer into a numpy array, but I
>     rather
>     > avoid having to read in the whole raster layer. I can also from
>     within the
>     > script run r.random  to generate a raster layer, r.stats to
>     export the
>     > resulting raster layer as a text file (with n flag), and than
>     read in the
>     > text file in Python. But I wonder if there is not a more direct
>     way to
>     > accomplish this..
>     >
>     >
>     > You can read col and row from GRASS Region and use random python
>     function
>     > to calculate random x and y and later query a pygrass raster object
>     >
>
>
>     Thanks. And what if I have a mask or null values in the target raster.
>
>
>     >
>     > Cheers,
>     >
>     > Paulo
>     >
>     >
>     > Cheers
>     > Luca
>
>
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