RE: Re: Best way to find near people

I use .extra(where=[where])

and something like this (measures km, not miles):
( 6378.137 * acos( cos( radians(long) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians(lat) ) + sin( radians(long) ) * sin( radians( latitude ) ) ) ) < 10

latitude and logitude are db-fields, 6378.137 the radius of the earth, long/lat my current position, searches for objects in a 10 km circle

regards

Henrik

>reply to message:
>date: 30.07.2010 07:30:30
>from: "Jani Tiainen" <redetin@gmail.com>
>to: django-users@googlegroups.com
>subject: Re: Best way to find near people
>
>> On Jul 29, 2010, at 2:58 PM, Alexandre González wrote:
>> > Hi!
>> >
>> > I'm searching near people in my app. I'm doing it a this way:
>> >
>> > 37 people = Person.objects.all().exclude(user=request.user)
>> > 38
>> > 39 near_people = list()
>> > 40 for person in people:
>> > 41 if self.is_near(me.coordinates, person.coordinates):
>> > near_people.append(person)
>> >
>> > Now, I'm getting all the the Person objects. This is a inefficient way.
>> >
>> > The coordinates are latitude/longitude coordinates, so I think in test
>> > the variation and get only latitude +/- 1 and longitude +/- 1 and after
>> > this, do the test exactly (the funcion is_near).
>> >
>> > But instead this, can I "draw" a circle and search only Person objects
>> > inside it?
>>
>> I'm not sure what database you are using, but if you are using PostgreSQL,
>> it has built-in geometric operators specifically for this kind of thing.
>> You might have to drop down into SQL, but in 1.2, that's nice and easy.
>>
>> The PostgreSQL documentation on this is at:
>>
>> http://www.postgresql.org/docs/8.4/interactive/datatype-geometric.html
>> --
>> -- Christophe Pettus
>> xof@thebuild.com
>
>Or if spatial operations are really needed, why not to use real spatial
>database and GeoDjango (django.contrib.gis). Spatialite, Postgis, Mysql or
>oracle. All supports at spatial to some extent. And there you can do easily
>simple filtering:
>
>Person.objects.filter(person_coordinates__dwithin(me.coordinates, distance))
>
>..and geodjango + spatial engine behind it will take care of all that complex
>stuff.
>
>Note: you can still use GEOS parts from geodjango to do calculations so you
>don't have to reinvent wheel if you want to keep coordinates as you already
>have.
>
>--
>
>Jani Tiainen
>
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