Exception hides dependency isssue

Hi,

On my first attempt to setup django-rest-framework-gis, I stumble upon an exception thrown here:

https://github.com/djangonauts/django-rest-framework-gis/blob/master/rest_framework_gis/fields.py#L44

So I put together a small example:

>>> import json
>>> t = json.dumps({ "type":  "Point", "coordinates":[45.563237,-73.582419]})
>>> t
'{"type": "Point", "coordinates": [45.563237, -73.582419]}'
>>> GEOSGeometry(t)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/srv/app/.virtualenvs/env/local/lib/python2.7/site-packages/django/contrib/gis/geos/geometry.py", line 64, in __init__
    raise ValueError('Initializing geometry from JSON input requires GDAL.')

which shows that the underlying issue was related to a missing library (python-gdal).

I think it’s Ok to return a ValidationError but I think it might make sense to also add the message from the captured exception so users know what went wrong.

What do you think?

[yoanisgil]

Ok. Will send you a PR then 😉

[mafuz]

Please am new in django I spend days trying to get pass this error to no avail when trying to migrate after installing geodjango

ValueError: String input unrecognized as WKT EWKT, and HEXEWKB.