[GRASS-dev] r.hydrodem addon fails on very big rasters (150, 000 x 120, 000 pixels)

[Markus Neteler]

On Thu, Feb 6, 2014 at 1:14 PM, Blumentrath, Stefan
<Stefan.Blumentrath at nina.no> wrote:
> Dear all,
>
> I am testing, trying, learning GRASS 7`s hydrology moduls at the moment. And
> I am very, very satisfied with the available tools. r.watershed managed to
> process a really big elevation model (150,000 x 120,000 pixels), which is
> amazing.

Wow! Please consider to add a note to
http://grasswiki.osgeo.org/wiki/GRASS_GIS_Performance#Large_raster_data_processing

(or in a blog entry or the like)

> However, when I use r.hydrodem addon on the same big grid with 150,000 x
> 120,000 pixels (with the memory option) I get the following warning (and
> finally error) message:
>
> r.hydrodem input=dem_10m memory=10000 output=dem_10m _hydro
...
> WARNING: segment_format(fd,1,-221837149,1,262144,16): illegal value(s)

This is an integer overflow of ncols etc:

[neteler at pgis_north r.hydrodem]$ grep nrows seg.c
seg_open(SSEG *sseg, int nrows, int ncols, int row_in_seg, int col_in_seg,

In r.watershed it is defined differently:

[neteler at pgis_north r.watershed]$ grep nrows seg/sseg_open.c
seg_open(SSEG * sseg, GW_LARGE_INT nrows, GW_LARGE_INT ncols, int
row_in_seg, int col_in_seg,
    if (0 > (errflag = segment_format(fd, nrows, ncols,

I suppose that this is an "easy" fix given the experience of r.watershed.
To not interfere, I'll leave the change to the module author.

Best,
markusN