Using UTM with geodjango

Question

I'm looking into using the UTM coordinate system with geodjango. And I can't figure out how to get the data in properly.

I've been browsing the documentation and it seems that the "GEOSGeometry(geo_input, srid=None)" or "OGRGeometry" could be used with an EWKT, but I can't figure out how to format the data.

It looks like the UTM SRID is: 2029

From the wikipedia article the format is written like this:

[UTMZone][N or S] [easting] [northing]

17N 630084 4833438

So I tried the following with no luck:

>>> from django.contrib.gis.geos import *
>>> pnt = GEOSGeometry('SRID=2029;POINT(17N 630084 4833438)')
GEOS_ERROR: ParseException: Expected number but encountered word: '17N'
>>>
>>> from django.contrib.gis.gdal import OGRGeometry
>>> pnt = OGRGeometry('SRID=2029;POINT(17N 630084 4833438)')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python26\lib\site-packages\django\contrib\gis\gdal\geometries.py", line 106, in __init__
    ogr_t = OGRGeomType(geom_input)
  File "C:\Python26\lib\site-packages\django\contrib\gis\gdal\geomtype.py", line 31, in __init__
    raise OGRException('Invalid OGR String Type "%s"' % type_input)
django.contrib.gis.gdal.error.OGRException: Invalid OGR String Type "srid=2029;point(17n 630084 4833438)"

Are there any example available to show how this is done?

May be I should just do any necessary calulations in UTM and convert to decimal degrees?
In this case does GEOS or other tools in geodjango provide convertion utitilites?

Answer 1

The UTM zone (17N) is already specified by the spatial reference system -- SRID 2029, so you don't need to include it in the WKT you pass to the GEOSGeometry constructor.

>>> from django.contrib.gis.geos import *
>>> pnt = GEOSGeometry('SRID=2029;POINT(630084 4833438)')
>>> (pnt.x, pnt.y)
(630084.0, 4833438.0)
>>> pnt.srid
2029

Then, for example:

>>> pnt.transform(4326)   # Transform to WGS84
>>> (pnt.x, pnt.y)
(-79.387137066054038, 43.644504290860461)
>>> pnt.srid
4326