[GRASS-user] Georrectification using points

[Hamish]

Hamish:
> you can add to the POINTS file manually (create some dummy test,
> points to see the simple text file format), or maybe more easily
> use gdal_translate to add the GCPs to a geotiff then import
> that.

Luisa wrote:
> Uhm my question is how can I create a Points file that is added to the
> group?

you can make a sample one to see the format by running one of the
interactive GUI control points modules, making up some data points,
and seeing how they look. (stored in $MAPSET/group/POINTS file).

here's an example:
#                   image                          target           status
#            east           north            east           north   (1=ok)
#
      7346.538713     8400.516178      170.733333      -45.766667    1
      5432.512633     8401.527487      170.700000      -45.766667    1
      3518.655562     8401.436787      170.666667      -45.766667    1
      5431.616447     5667.495309      170.700000      -45.800000    1
      3518.597469     5667.537313      170.666667      -45.800000    1
      3519.624691     2932.507550      170.666667      -45.833333    1
      1607.577726     2932.496469      170.633333      -45.833333    1


the important thing is that the 5 columns are in order and there is
some form of whitespace between them. In the above example I am going
from pixel coordinates in a simple_xy location to long/lat coords in a
LL location, and all GCPs will be used.

see also "gdal_translate" to set GCPs and SRS, and "gdalwarp" to perform
the rectification.

> Regarding  http://grass.osgeo.org/wiki/Georeferencing:
> What is the difference between NEW WAY and EXTRA NEW WAY ? Aren't they
> the same? 

mostly, but one is for the Tcl/Tk GUI tool, and the other for the wxPython
newer GUI tool.


Hamish