#2428: r.external to accept gdal config options
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Reporter: perrygeo | Owner: grass-dev@…
Type: enhancement | Status: new
Priority: normal | Milestone: 7.1.0
Component: Default | Version: svn-trunk
Resolution: | Keywords: r.external
CPU: x86-64 | Platform: Unspecified
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Comment (by dylan):
Replying to [comment:3 neteler]:
> Replying to [comment:2 glynn]:
> > Replying to [comment:1 neteler]:
> > > The request sounds reasonable but I didn't figure out how to pass
"papszOptions" to GDAL as used in r.external. The magic line in r.out.gdal
is this:
> >
> > > but in r.external GDALOpen() is used. Perhaps a GDAL expert can tell
us the trick.
> >
> > Note that r.external is the analogue of r.in.gdal, which doesn't
accept any configuration options.
>
> While it doesn't directly, I had added a larger cache some time ago by
setting GDALSetCacheMax() to 300MB rather than the tiny 40MB default GDAL
cache size. This speeds up import tremendously:
>
> {{{
> r.in.gdal ...
> memory=integer
> Maximum memory to be used (in MB)
> Cache size for raster rows
> Options: 0-2047
> Default: 300
> }}}
>
> I wonder how to get that into r.external (I suppose that it would
benefit as well).
>
> > If options are needed for reading, a similar option should be added to
both r.in.gdal and r.external, presumably using GDALOpenEx() instead of
GDALOpen(). The latter will require extending the GDAL "link" format
(lib/raster/gdal.c).
>
> OK (no idea how to implement that).
Finding this thread after searching for some ways to speed-up file access
to maps linked via `r.external`.
The adjustable cache solution in `r.in.gdal` appears to be:
{{{
if (parm.memory->answer && *parm.memory->answer) {
/* TODO: GDALGetCacheMax() overflows at 2GiB, implement use of
GDALSetCacheMax64() */
GDALSetCacheMax(atol(parm.memory->answer) * 1024 * 1024);
G_verbose_message(_("Using memory cache size: %.1f MiB"),
GDALGetCacheMax()/1024.0/1024.0);
}
}}}
Could this same block of code be used within `r.external`? I don't fully
understand how `r.external` works, so I suppose that it is more
complicated than this.
Or another option, is there an environmental variable that could be used
to control the GDAL cache size?
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Ticket URL: <https://trac.osgeo.org/grass/ticket/2428#comment:4>
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