Question: DistanceToPointFilter

[yamila-moreno]

Hi!
I'm trying to use the DistanceToPointFilter, but I cannot get it working.

This is my code:

class RouteView(viewsets.ReadOnlyModelViewSet):
    queryset = Route.objects.all()
    serializer_class = RouteSerializer
    filter_backends = (InBBoxFilter, DistanceToPointFilter, DjangoFilterBackend)
    filter_class = RouteFilter
    distance_filter_field = 'start_point'
    bbox_filter_field = 'start_point'
    bbox_filter_include_overlapping = True

I've tried all the combinations with these params:

routes/?dist=4000&point=lon,lat
routes/?dist=4000&point=lat,lon
routes/?dist=4000&point=lon,lat&distance_filter_convert_meters=True

etc... Am I missing something? [The other filters are properly working]
Thanks for your help :D

[nemesifier]

Should be right, provided lon and lat are two floats.

You may want to take a look at the DistanceToPointFilter code to understand how it works.

[yamila-moreno]

Hi, lat and lon are floats, as expected. I checked the code before asking. I'll keep trying.

[nemesifier]

Check also the test:
https://github.com/djangonauts/django-rest-framework-gis/blob/master/tests/django_restframework_gis_tests/test_filters.py#L130

I tried to use this feature a while ago (more than 1 year) and I remember it worked, but since then I have not tried anymore. Since I didn't add the feature myself I can be sure the feature works correctly just as long as the test works too, assuming the test code doesn't contain an hidden flaw.

Let me know what you find.
Thanks.

[tobias47n9e]

@yamila-moreno This is just a wild guess: If you happen to run the a Spatialite database the filter won't work because Spatialite does not support dwithin.

Source: https://docs.djangoproject.com/en/1.10/ref/contrib/gis/db-api/#spatial-lookup-compatibility

[Gagaro]

I have the same issue. I'm using postgis and I can't make this filter work properly.

This may be related to my DB. The filter done is :

queryset.filter(geometry__dwithin=('POINT(-104.590948 38.319914)', 1))

And it returns a point which is ~10 km away. I'm not sure how to debug further however.

EDIT: The generated SQL is :

SELECT "geodirectory_entry"."id", "geodirectory_entry"."owner_id", "geodirectory_entry"."geometry" FROM "geodirectory_entry" WHERE ("geodirectory_entry"."owner_id" = 1 AND ST_DWithin("geodirectory_entry"."geometry", ST_GeomFromEWKB('\001\001\000\000 \346\020\000\000\315\314\314\314\314,Z\300*\304#\361\362(C@'::bytea), 1.0))

[Gagaro]

You actually need to set distance_filter_convert_meters on the view itself.

class MyViewSet(viewsets.ModelViewSet):
    filter_backends = (
        DistanceToPointFilter
    )
    distance_filter_convert_meters = True

[tobias47n9e]

@Gagaro I think by default the coordinate system is WGS84 (EPSG: 4326). So the request with '1' should return all points in a circle with roughly 111 km diameter.

[Gagaro]

Yes that was my issue. So the distance_filter_convert_meters parameter should be enough right?

[tobias47n9e]

@Gagaro At least for me it works if I set distance_filter_convert_meters in the view class. I can look up a point by focusing on a point roughly 1° away and setting the dist to around 100 000 meters.

Testing to look up a point at 0 lon 0 lat: In degrees 0 lon 1 lat needs distance of at least 1°. That means that dwithin probably counts points at the very edge of the circle as inside of the polygon. When using meters the point is filtered at around 111400 meters.

Seems like everything is working as expected.

[Gagaro]

All right, thanks the help 👍 , I'm fairly new to gis development.

[nemesifier]

Hey people, I prefer this github issue tracker to be used as a bug-tracker. Therefore if any of you think there's a bug, please send a failing test.

For questions and discussions, we have two other instruments that are very useful:

• stackoverflow (using the django-rest-framework-gis tag) for specifc questions
• mailing list for general discussions