[GIS] Negative UTM easting

coordinate systemutm

I am trying to do the following calculation:

  1. Given lat,lon of a point (center of a rectangular (in UTM) domain), I find its UTM coordinates.
  2. Given domain width and length, I find coordinate of its 4 corners in UTM
  3. Finally, I need to find lat,lon coordinates for the corners

I'm having a problem with step 2, because one of the corners is outside of the UTM zone in which the center point is located. So I get negative easting numbers and can't figure out how to do the lat,lon conversion. I'm supposing that I need to find the new UTM zone for that point, but I don't know exactly how.

Additional info: I'm using this little Python library to do the UTM<->lat,lon conversion https://github.com/Turbo87/utm It doesn't seem to handle negative eastings.

Best Answer

For the conversion, it is necessary to stick to the same UTM zone for all points. As metioned in the comments, it is possible to leave the zone of definition of the UTM zone to some extent.

This is mathematically limited to about 20° east and west of the central meridian. Outside you would get reprojection artefacts, but you would see that in your source data already.

I would suggest to use the GDAL library for any projections. It is accessible via python as well, and used by QGIS and many other softwares.

Apart from that: The central meridian of UTM is at 500.000 metres, and the zone is in Europe about 400km wide. I wonder how large your rectangle is to get negative values. Unless you are somewhere around the poles, of course.

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