[Gdal-dev] Different UTM Zones...

[Tyler Mitchell]

On August 7, 2004 06:48 pm, StefanReisser at t-online.de wrote:
> Hi!

Hi Stefan - lots of questions!  That's good :)

> I have a huge GeoTiff image and I want to extract that part, that
> perfectly matches a specific DEM file.
> It's easy, as long as both the image and the DEM use the same projection
> and geographic coordinate system.
>
> However, if the UTM zones are different, or the geographic coordinate
> system is different, how can I compute the raster coordinates
> of the DEM inside the GeoTiff image?
>
> How can I convert coordinates between different UTM zones and
> furthermore, how can I convert between Lat/Long and UTM coordinates?

A Proj4 utility called cs2cs (coordinate system 2 coordinate system) will 
probably do the trick for you, unless you want to actually reproject your 
datasets.

Get the extent of the DEM and put the pair of coordinates (one x y pair per 
line) into a text file.  Then run cs2cs with a few options to have those 
coordinates reprojected and printed to your screen.

For example:
Contents of utm.txt (easting, northing)
--------------
5500000 450000
--------------

Project from one UTM zone to another:
> cs2cs +proj=utm +zone=10 +to +proj=utm +zone=11 utm.txt
Outputs:
4649861.81      414740.36 0.00  (0.00 is elevation which I left blank)

To project from UTM to lat/long:
> cs2cs +proj=utm +zone=10 +ellps=GRS80 +to +proj=latlong utm.txt
123d41'33.592"W 49d39'1.696"N 0.000

If your file has y then x (as opposed to x then y which is default) add the 
option "-r" to the command.

So using cs2cs you should be able to get the projwin coordinates you need to 
use gdal_translate to cut out a piece of an image you are interested in.
> gdal_translate -projwin <upper left x> <upper left y> <lower right x>< lower 
right y> image1.tif clipped.tif
Will clip the area you want.

You could then, optionally reproject  from one coordinate system to another 
using gdalwarp.

Let us know if you need more help using these utilities.

Enjoy.

Tyler