[GRASSLIST:6973] Re: georeference vector map and transform from
xy location to long/lat projection
rathgeber2000 at yahoo.de
Wed Jun 1 15:25:33 EDT 2005
Markus Neteler schrieb:
> On Mon, May 30, 2005 at 09:53:01PM +0200, Andreas Rathgeber wrote:
>>I have a outside of GRASS digitized vector map (original map was
>>image with distortion and some rotation) loaded into an XY
>>location. This location also contains the original image.
>>Now I want to georeference both maps into my target location that
>>has a long. / lat. projection.
>>I've created a pointsfile based on the original image. I have no
>>problem to georeference the image into my target location with
>>the target projection.
>>Where I struggle is the georeferencing of my vector map into the
> If you want to apply only linear stretch etc., load the vector
> map directly into the target location and then use v.transform.
Thanks for your help. I did solve it with v.transform. Here is the
description how I exactly did it:
1) create a new xy location and Import the pixel image. Then
create an image group and create a pointsfile based on this
image. Save the points file from within i.points.
2) Import the vector map into the temp xy location. Make sure
that your vectors start also at the same coordinates eg. x=0 and
y=0. Check it by displaying the image first and then the vector.
3) Export with OGR into a shape file or one of the other types.
4) Import the vector map into the target long./lat. location, but
for this vector map use the -o option in the OGR that ignores the
regions setting of your current region.
5) Use v.transform and the pointsfile from your x,y location to
rectify your image. Unfortunately this way only a 1st order
tranformation is possible. But better than nothing.
6) Voila I have it. Maybe it is just enough to skip steps 2) and
3) and directly load into the target location.
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