fairdm.utils.location.managers#

Lookups that find records by where they are.

Module Contents#

Classes#

Spatial

Read what a lookup is given, and build the expressions its queries compare.

LocatedQuerySet

Queryset methods for a model that holds its own location.

Data#

WGS84

API#

WGS84#

4326

class Spatial#

Read what a lookup is given, and build the expressions its queries compare.

Every method is static: the class only groups what the lookups of this module share.

static polygon(area)#

Read an area as a polygon in WGS 84.

Args: area: A GEOS polygon, or a (west, south, east, north) tuple in degrees. A tuple with west greater than east is a box across the 180th meridian, the shape spatial_coverage returns.

Returns: The polygon, in SRID 4326.

static point(point)#

Read a point as a WGS 84 point.

Args: point: A GEOS point. One without a reference system is taken to be in WGS 84.

Returns: The point, in SRID 4326.

static distance(distance)#

Read a distance as a measure.

Args: distance: A D measure, or a number of metres.

Returns: The distance as a D.

static geography(field='location')#

Cast a point column to a geography, the expression the geography indexes are built on.

Args: field: The name of the point column or annotation.

Returns: The cast expression.

class LocatedQuerySet#

Queryset methods for a model that holds its own location.

Mix it into a model’s queryset. Each method returns a queryset, so it combines with any other filter, visible_to() included.

Example: python     Sample.objects.inside((8.0, 47.0, 9.0, 48.0))     Sample.objects.within_distance(Point(8.4, 48.9, srid=4326), D(km=5))     Sample.objects.nearest(Point(8.4, 48.9, srid=4326))[:10]    

inside(area)#

Return the records whose location lies in an area. A point on the edge counts.

Args: area: A GEOS polygon, or a (west, south, east, north) tuple in degrees.

Returns: The records inside the area. Records with no location are never inside.

within_distance(point, distance)#

Return the records whose location is within a distance of a point.

The distance is measured on the ground, not in degrees, so the answer is the same near the equator and near a pole.

Args: point: A GEOS point. distance: A D measure, or a number of metres.

Returns: The records within the distance.

nearest(point)#

Order the records by their distance from a point, nearest first.

Args: point: A GEOS point.

Returns: The records ordered by distance, each carrying distance as a D measure, or None for a record with no location, which comes last.