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

[Glynn Clements]

Markus Neteler wrote:

> this is excellent! Thanks so much. I have tested it but no success yet:

> >> Tomorrow, I'll look into creating an r.external module, adding null
> >> support, etc.
> >
> > Okay, done (well, enough to try it out without having to manually hack
> > the files; null support is absent).
> 
> [for my convenience I have copied it over to GRASS 6.4.svn locally]

Copied what over? r.external won't work unless the corresponding
lib/gis changes have also been incorporated, and lib/gis was built
with GDAL_LINK=1:

> At present, r.external is built automatically, but the code to read
> linked maps is conditionalised upon GDAL_LINK, so you need to build
> with "make GDAL_LINK=1". If you forget that part, r.external will
> work, but attempting to read the map will fail (the cell/fcell files
> are zero-length).

Your errors are consistent with lib/gis not having the necessary
support. Does:

	nm $GISBASE/lib/libgrass_gis.so | fgrep gdal

produce any output? There should be at least:

	T G_close_gdal_link
	T G_get_gdal_link
	t gdal_values_double
	t gdal_values_float
	t gdal_values_int
	t read_data_gdal

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