[R-sig-Geo] read GRASS6 from outside

[Roger Bivand]

On Thu, 13 Nov 2008, Patrick Giraudoux wrote:

> Dear listers,
>
> I am using GRASS6 embedded within QGIS under Windows for teaching purpose. 
> This prevents reading GRASS objects from R within GRASS (R cannot be launched 
> within GRASS in this configuration).

Patrick,

Could you explain why not? I can launch it, and I know others can, at 
least by:

Plugins -> GRASS -> Open GRASS Tools -> shell

and typing the full path to Rgui.exe at the shell prompt, for me:

$ "C:/Program Files/R/R-2.8.0/bin/Rgui.exe"

You may need to set the path to R_LIBS in user environment variables, or 
to add it to the command line in the GRASS shell prompt, or use 
.libPaths() within R, but beyond that, things should work, including file 
transfer etc.

The startup message in the current release does say "GRASS not running" 
because QGIS does not set the GRASS_VERSION or LOCATION_NAME environment 
variables, but does set GISRC - I'll try to fix that.

Doing getwd() in R will show that R is in the QGIS MSYS home directory for 
the user. This of course places R "on top" in standard spgrass6 fashion, 
but QGIS can be used at the same time. Work is progressing to embed R 
within QGIS, see:

http://www.ftools.ca/manageR.html

but until this is up and easily installable, going through the GRASS shell 
seems to work. Note that when you do system() from R, QGIS expects all 
executables to have the .exe extension added:

system("g.list rast") # fails
system("g.list.exe rast") # succeeds

Hope this helps,

Roger

PS. Note that the QGIS MSYS GRASS shell does history, so it logs the 
command to start R, which you retrieve with the up arrow in the usual way 
- the only editing needed is when you upgrade R.

>
> I was wondering if it would be possible to read GRASS objects (vector, raster 
> layers, region values, etc.) in R (eg to sp objects) from outside GRASS, with 
> functions analogous to those  provided with spgrass6.

PPS. In desperation, use v.(in/out).ogr and r.(in/out).gdal matched with 
read(GDAL/OGR) and write(GDAL/OGR) in rgdal, but watch which directory 
they land in.

>
> Any idea welcome.
>
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no