[GRASS-user] GRASS GIS virtual raster data sets

[Markus Neteler]

On Wed, May 30, 2018 at 4:21 PM, Nikos Alexandris
<nik at nikosalexandris.net> wrote:
> Dears,
>
> I guess there is no GRASS GIS built-in implementation of GDAL's VRT
> concept (several related ideas listed
> https://trac.osgeo.org/grass/wiki/Grass8Planning).

I wish to see that as well (and discussed it a while ago with our dear
Markus M...

GRASS GIS would gain a lot having the possibility to virtually mosaik
raster tiles.

> Once past some compilation issues, I am about to try to build a VRT
> based on native GRASS GIS raster maps (using GDAL with support for GRASS
> GIS raster data), then link to this VRT via `r.external` from inside a
> regular Mapset.

Interesting, will that not cause loop dependencies?

I thought of true internal support for that to avoid loops.

> As a side-note, an image without pre-computed statistics stored in its
> metadata, will require some time for `r.external` to work. The latter
> likely forces  this computation.
>
> Perhaps it is faster to use `gdalinfo`'s '-stats' option to do this.
>
> I wonder if there are smart ways to build, in GRASS GIS' data base,
> a larger virtual raster map out of many smaller ones, without the need
> to actually patch the latter ones in a new raster map file.

I guess that some C code needs to be touched in lib/raster/ to allow
for a VRT-style raster concept.
Maybe we missed the current GSoC train for this idea :)

markusN