[GRASS-user] External Database and projections

[Dylan Beaudette]

The use of r.external makes a lot of sense when dealing with very large
files. Does the use of "external" files work as expected in all of the new
t.* modules?

Thanks,
Dylan

On Wed, Oct 7, 2015 at 12:09 PM, Markus Neteler <neteler at osgeo.org> wrote:

> On Wed, Oct 7, 2015 at 12:55 PM, Blumentrath, Stefan
> <Stefan.Blumentrath at nina.no> wrote:
> ...
> > My suggestion is to not use PostGIS for big rasters, unless you have to,
> > because you want to use the data in a specific application for example.
>
> Note r.external and r.external.out of GRASS GIS 7 for avoiding data
> duplication:
>
> https://grass.osgeo.org/grass70/manuals/r.external.html
> https://grass.osgeo.org/grass70/manuals/r.external.out.html
>
> Here an example:
>
> # register (rather than import) a GeoTIFF file in GRASS GIS:
> r.external input=terra_lst1km20030314.LST_Day.tif output=modis_celsius
>
> # define output directory for files resulting from subsequent calculations:
> r.external.out directory=$HOME/gisoutput/ format="GTiff"
>
> # perform calculations (here: extract pixels > 20 deg C)
> # store output directly as GeoTIFF file, hence add the .tif extension:
> r.mapcalc "warm.tif = if(modis_celsius > 20.0, modis_celsius, null() )"
>
> # cease GDAL output connection and turn back to write standard GRASS
> raster files:
> r.external.out -r
>
> # use the result elsewhere
> qgis $HOME/gisoutput/warm.tif
>
> Best
> Markus
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