[GRASS-user] r.hazard.flood does not respect region settings?

[Hamish]

maning wrote:

> I'm testing r.hazard.flood and noticed that it computes the flood and
> mti layers on the full region of the elevation raster instead of the
> pre-defined region settings.
> 
> The relvant code I found from the r.hazard.flood is this:
>    # Detect cellsize of the DEM
>     info_region = grass.read_command('g.region', flags = 'p', 
> rast =
> '%s' % (r_elevation))
>     dict_region = grass.parse_key_val(info_region, ':')
>     resolution = (float(dict_region['nsres']) + 
> float(dict_region['ewres']))/2
>     grass.message("Cellsize : %s " % resolution)
> 
> Would it be possible to either respect the current region settings or
> add a flag to choose between the dem region settings or current region
> settings?


if it needs to detect the original raster cell resolution (usually that's only needed to avoid aliasing artifacts in certain situations) it should use r.info to get the answer. I'm guessing due to the averaging of the ew and ns resolutions avoiding aliasing isn't the case.

if a module wants to change the region (and almost none should ever do that except for g.region by itself) it should set up a temporary WIND_OVERRIDE first, in the case of python scripting there is an easy grass python function to make that and clean it up at the end. (otherwise parallel jobs get their regions messed up mid-run, and region changes without you expecting it will)

I suspect grass.raster's raster_info() is the better way for r.hazard.flood to do what it's trying to do now. But also just querying the current g.region info without changing anything is probably even better, as that is what the other raster commands will expect to use. If the user should align perfectly with the input map first, it should be noted in the help page for them to do it manually before running the module.


regards,
Hamish