[gdal-dev] using gcp's without giving coordinates

[Klokan Petr Přidal]

Hi,

I am not familiar with OziExplorer Map files, but I have seen a
project trying to implement what you need, maybe you can reuse it (and
probably improve it and add support of different projections):

http://ozi2geotiff.svn.sourceforge.net/viewvc/ozi2geotiff/trunk/ozi2geotiff.py?view=markup

I guess you would like to have affine transformation georeference from
your GCPs points in your example with gdal_translate.
Then you should either warp your raster with gdalwarp utility or use a
tool like gcps2wld.py to calculate a best fitting World file and keep
raster as it is.

Klokan

P.S.
A standalone application for World file generation then you can use
independently on GDAL is:
http://blog.oldmapsonline.org/2008/06/georeferencing-images-by-control-points.html
or very simple python script doing the calculation as well:
http://code.google.com/p/oldmapsonline/source/browse/trunk/gcps2wld/python-no-dep/gcps2wld.py

2009/3/30 erik <whatevar89 at gmail.com>:
> Hello,
>
> I'm trying to convert a map from OziExplorer Map file fromat to Geotiff.
> FOr this i'm using the calibration points in the Map file as Ground Control
> Points.
>
> I do the following:
>
> gdal_translate \
> -gcp 203 52 529000 4191000 \
> -gcp 5174 3096 544000 4182000 \
> -gcp 5201 99 544000 4191000 \
> -gcp 176 3051 529000 4182000 \
> -gcp 1861 1067 534000 4188000 \
> -gcp 3517 2081 539000 4185000 \
> -gcp 3526 1083 539000 4188000 \
> -gcp 1851 2066 534000 4185000 \
> -gcp 2844 2742 537000 4183000 \
> -a_srs "+proj=utm  +ellps=intl  +k=0.999600  +x_0=500000.0  +y_0=0.0
> +zone=30  +units=m
> +towgs84=-125.098545,-76.000054,-156.198703,0.0,0.0,-1.129,8.30463103
> +no_defs" \
> map.bmp \
> map.tif
>
> However doing this still gives the maps upper left corner start at 0-0.
> I was wondering if there was a way to make gdal infer the correct corners of
> the map from the gcp's without specifying them directly.
> Or is there another way to achieve this without specifying the coord
> corners? (The calibration points are not corner-based)
> One solution would be to calculate the corners myself programmatically (from
> the pixels), but this would be the least good solution.
>
> Many thanks,
> Erik
>
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>



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