[GRASS-user] r.in/out.xyz question

[Glynn Clements]

Frank Broniewski wrote:

> I am experimenting with r.in/out.xyz. As far as I understand, r.out.xyz take a 
> cell center coordinate and writes this and the associated z value into 
> something(stout/file).
> Now I have recognised while importing the output with r.in.xyz that there is a 
> different cell count with different rasters while the region is the same.
> 
> I have a region with 670480 cells (986 x 680). Each test raster (srtm data and 
> derived slope from srtm) says the same with r.info.
> 
> Now I get different messages from r.in.xyz for the cell count: The correct 
> number of cells for the srtm data (670480 ) but another for the slope raster 
> (667152). Checking the output files, the number of lines differ: 67048 lines 
> for the srtm and 667152 lines for the slope raster.
> 
> I am sorting the output by the z value in order to create classes of equal 
> area and the import from the slope raster doesn't work as expected, there's a 
> large amount of cells associated to the * - value (Null I presume) instead of 
> the classes I defined.
> 
> From the manual I read that NULL values are not exported by r.out.xyz. Is 
> there maybe a problem with 0 (degree) values from slope?

667152 = 984 * 678 = (986-2) * (680-2)

IIRC, r.slope.aspect needs a 3x3 window to compute the slope, so it
cannot compute the slope for the boundary cells, so the result has a
1-cell-wide border of null cells.

-- 
Glynn Clements <glynn at gclements.plus.com>