[GIS] GeoDjango: Order by distance for model that has a ForeignKey relation to another model that has a PointField

geodjango

Model A has a ForeignKey relation to Model B. Model B has a PointField. Is there a way to order Model A objects by distance from a POINT?

Best Answer

Assuming that both Model A and B are using objects = models.GeoManager(), the FK field on Model A is named b, Model B has PointField named point, and pnt is a GEOSGeometry then the following should work:

A.objects.distance(pnt, field_name='b__point').order_by('distance')

Related Solutions

[GIS] GeoDjango: order PointField by distance

Just change

cities = City.objects.filter(location__within=boundaries)

cities = City.objects.filter(location__within=boundaries).distance(centre).order_by('distance')

Each City object will also have a 'distance' attribute.

[GIS] Best GeoDjango MySQL workaround for distance queries

You created a geo-model without expliciting the srid. This means that your geometries will default to 4326 (also known as WGS84, units are in degrees of longitude and latitude).

If you would be using PostGis < 1.5 for performing spatial queries using a distance like the buffer method does, you would need first to project your point to a projected system (most general is 900913, but there may be much better ones, depends on the zone of the world where your point is located), then create the buffered polygon, then reproject back the polygon to 4326, finally use this polygon in the within filter.

This should also apply to MySql, AFAIK.

If you would have the possibility of using PostGis 1.5, then you could create your model with geographic data type by using a GeometryField.geography option set to true [0]

[0] http://docs.djangoproject.com/en/dev/ref/contrib/gis/model-api/#geography

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Related Solutions

[GIS] GeoDjango: order PointField by distance

[GIS] Best GeoDjango MySQL workaround for distance queries

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