#22830: GeoDjango dwithin errors when using django.contrib.gis.measure.D
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Reporter: django@… | Owner: nobody
Type: Bug | Status: closed
Component: GIS | Version: 1.6
Severity: Normal | Resolution: invalid
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by django@…):
Replying to [comment:1 claudep]:
> The error message is pretty clear. As your objects are in geographic
coordinates (geometry fields default to WGS84), you have to provide the
distance as degree units. This is for example matching the PostGIS
definition:
> {{{
> boolean ST_DWithin(geometry g1, geometry g2, double precision
distance_of_srid);
> }}}
> `distance_of_srid` being degrees for WGS84. So the `5` that works in
your example means 5 degrees, not 5 km!
>
> You could argue that !GeoDjango could automatically cast geographic
fields to geometry types when distance is a `Distance` object. It is
unfortunately not as smart currently. See #17635 for a similar feature
request (but in the opposite direction).
The error may be clear, but the cause isn't (which is why I had to submit
this bug report). Either GeoDjango should correctly handle `Distance`
objects in all cases, or the documentation should be edited to make it
clear that `Distance` objects don't work in all cases. Since #17635 has
been open for 2 years without any progress, I'd opt for the latter. I
don't see anywhere in the documentation that even hints that `Distance`
objects can't be used for the dwithin query in certain cases.
--
Ticket URL: <https://code.djangoproject.com/ticket/22830#comment:2>
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