r.external - was: Re: [GRASS-dev] some questions about future development

[Markus Neteler]

On Wed, Aug 20, 2008 at 4:03 PM, Glynn Clements
<glynn at gclements.plus.com> wrote:
> Glynn Clements wrote:
>
>> Known issues at present:
>>
>> Null support is missing (r.external records any null value reported by
>> GDAL, but G_get_raster_row() etc ignore it; I suspect that it will
>> treat zero as null due to the absence of a null file).
>
> Null support has been added.

I have now tested (in my local 6.4 backport) a shaded terrain map (GeoTIFF).
The 0 pixels are registered as NULL pixels, leading to white areas instead
of black in case of cast terrain shadow.

So I confirm that zero is treated as NULL now.
Could the GDAL Null value be used instead?

gdalinfo /home/neteler/data/maps/srtm/srtm_alps_LCC_hillshaded.tif | tail -n 2
Band 1 Block=8378x1 Type=Byte, ColorInterp=Gray
  NoData Value=-9999

The function is according to gdalinfo.c:

double dfNoData;
int bGotNodata;
dfNoData =  GDALGetRasterNoDataValue( hBand, &bGotNodata );

thanks,
Markus