[GRASS-user] Problem with v.digit

[Hamish]

Nikos Alexandris wrote:
> If you need to georeference an image you can "play" first in the
> corners trying to nail your image (as like when you want to hang a
> poster in the wall!) and then move more in the inner locations and
> successively in the centre.

There is a little known but neat feature in the i.vpoints
georeferencing module to reverse-project a vector layer from the target
location over the source raster image that you are trying to create
GCPs for, using the current set of tie points.

Once you have created some GCPs click the "ANALYZE" -> "OVERLAY" button
to chose an overlay vector from the target mapset.

i.vpoints is also interesting from the fully visual "parallel click"
interface. You click on a spot on the source image in the left pane,
then click on the matching point on the raster or vector map (from the
target mapset) on the right pane. From those two clicks it grabs and
fills in the source+target coordinates for you. This can be a very
quick way of georeferencing a map. Once you have done a few GCPs you
can then reverse-overlay the vector to test how it looks.


Maybe this could oneday make it into the new GUI georeferencing tools?


Hamish



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