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

[Frank Warmerdam]

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,
-- 
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