[GRASS-user] Where are ground control points?

[Hamish]

Andres Kuusk wrote:
> I have seeked in manuals and in the GRASS-user arhives (for 2006) but
> no success.
> Where are stored the ground control points which are marked with 
> i.points? And in which form?

a file called "POINTS" in $MAPSET/group/$GROUPNAME/.

it's a simple human readable text file.

> Is there any possibility to use the ground control points for
> i.rectify created somewhere else and stored in a file?

yes, just cut and paste into the exact textfile format POINTS uses.
AFAIK this is what the new TclTk Georectifyer in gis.m does.

alternatively use gdal_translate to add GCPs to a GeoTIFF and use
gdalwarp to do the rectification. See the i.warp shell script on the
wiki add-ons page. Mind the differing conventions WRT raw image 0,0
being top or bottom left.

another thing to note: i.vpoints has a lot of neat features which
i.points doesn't, like overlay of an inverse projected vector file to
preview results.


Hamish