[gdal-dev] Transform point from UTM to Lat/Long

[Jorge Arévalo]

On Mon, Feb 21, 2011 at 7:01 PM, Frank Warmerdam <warmerdam at pobox.com> wrote:
> On 11-02-21 12:43 PM, Jorge Martin wrote:
>>
>> Hello,
>>
>>
>>         I have a big doubt about transforming one point from UTM to
>> Lat/long.
>> I have to make the resampling of a Lat/long image. The target image is UTM
>> with
>> 2.5 resolution. To create the target image I use GDAL, so I have to set
>> the UTM
>> zone, so I set this zone to the zone corresponding to the top left corner
>> of
>> the source image (Lat/long).
>>
>>       When I am reading the all the points of the target (UTM) image and
>> finding the corresponding lat/long coordinates into the source image. I
>> have to
>> transform these points from UTM to Lat/Long. I case the source image
>> covers
>> more than one UTM zone, the transformation between this two coordinate
>> system
>> is not the right.Because the Lat/long of the initial image may corresponds
>>  to
>> a UTM zone different than the one I have fixed for the grid.
>>
>> Is there any way to make this transformation taking into account this
>> problem?
>
> Jorge,
>
> I'm not positive I follow your problem, but in the situation of resampling
> an image into a UTM projection when the image overlaps two zones you can
> just pick one with the greatest overlap and use that.
>
> There is nothing that says you can't reproject to a given utm zone even
> outside it's zone bounds.  But keep in mind that the further you get
> from the central meridian of a zone, the greater the distortion and error
> in how the equations are evaluated.  So you don't want to be using a
> UTM zone several zones away from the image.
>
> As a rule of thumb, I'd suggest using the center of the image to decide
> on a utm zone.
>
> Best regards,
> --
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Programmer for Rent
>
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Hi Jorge,

As Frank said, I'd use the center of the image to decide UTM zone. I
have experience with images covering Spain area (UTM zone 28 for
Canary Island, and 29-31 for Spain). I've obtained positive results
using zone 30 for all Spain except Canary Island.

Best regards,

-- 
Jorge Arévalo
Internet & Mobilty Division, DEIMOS
jorge.arevalo at deimos-space.com
http://es.linkedin.com/in/jorgearevalo80
http://mobility.grupodeimos.com/
http://gis4free.wordpress.com
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