Re: GeoDjango: default 4326 SRID doesn't work for transform()

On 08/29/2010 07:45 PM, kyleduncan wrote:
> Hi all,
>
> I am trying to do obtain the distance between two users on my site,
> using code I found in this group. We already have geoDjango installed,
> though i'm wondering if my problem comes from being on an old version
> (i dont know which version we're using - if somebody could tell me how
> to check that would be great). We are running Django 1.1

Well, then you're using the geodjango bundled with django 1.1. I don't
remember seeing big changes in django 1.2's changelog regarding
geodjango. So you ought to be OK with that.

> the code i am using is:
>
> from django.contrib.gis.geos import Point
> from django.contrib.gis.measure import D
>
> my_location = request.user.get_profile().location
> their_location = other_user.get_profile().location
>
> my_location.transform(4326)
> their_location.transform(4326)
> distance = my_location.distance(their_location)
>
> if request.user.get_profile().get_preferences().use_metric
> == 1:
> distance_result =
> round(D(m=my_location.distance(their_location)).km, 1)
> else:
> distance_result =
> round(D(m=my_location.distance(their_location)).mi, 1)
>
> the last section is just a check to see whether the user wants the
> result in miles or km. the bit that's troubles me is the transform()
> section. if i put in 4326, i just get 0.0 as the result. if i put in
> nothing so it's just transform() (which i understand should use 4326),
> i get this django Error:
>
> TypeError at /members/GayHopHelper/
>
> transform() takes at least 2 arguments (1 given)
>
> the only thing that works so far is using SRID 32140, which is for
> south texas. the results seem ok but definitely a bit inaccurate,
> which is to be expected.

I only recently started using geodjango, so I'll just spit out a few
brainstormy ideas without any real solution:

- What's the coordinate system of your user's location data?

- Why transforming before grabbing the distance? Can't you transform
afterwards?

- If you're using the google projection somewhere: did you add it to
your geo database? There's a note somewhere in geodjango's doc about
that 900973 projection. Not having it could throw off a calculation.

- There's also a hint in that doc about a NULL projection that you need
to add to your proj4 or whatever files to enable proper transformations.

Just a brainstorm to get you started ;-)

Reinout

--
Reinout van Rees - reinout@vanrees.org - http://reinout.vanrees.org
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