[GRASS-user] Where are ground control points?

GRASS GRASS user
1

Hi!

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?

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

Thanks!

Andres Kuusk
Tartu Observatory, Estonia

2

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?

look into the files stored in location/mapset/group directory

And in which form?

text

Maciek

3

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