django1/docs/ref/contrib/gis/serializers.txt

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==================
GeoJSON Serializer
==================
.. module:: django.contrib.gis.serializers.geojson
:synopsis: Serialization of GeoDjango models in the GeoJSON format.
GeoDjango provides a specific serializer for the `GeoJSON`__ format. See
:doc:`/topics/serialization` for more information on serialization.
The GDAL library is required if any of the serialized geometries need
coordinate transformations (that is if the geometry's spatial reference system
differs from the ``srid`` serializer option).
.. versionchanged:: 1.9
The GeoJSON serializer no longer needs GDAL if all geometries are in the
same coordinate system as the ``srid`` serializer option.
__ http://geojson.org/
The ``geojson`` serializer is not meant for round-tripping data, as it has no
deserializer equivalent. For example, you cannot use :djadmin:`loaddata` to
reload the output produced by this serializer. If you plan to reload the
outputted data, use the plain :ref:`json serializer <serialization-formats-json>`
instead.
In addition to the options of the ``json`` serializer, the ``geojson``
serializer accepts the following additional option when it is called by
``serializers.serialize()``:
* ``geometry_field``: A string containing the name of a geometry field to use
for the ``geometry`` key of the GeoJSON feature. This is only needed when you
have a model with more than one geometry field and you don't want to use the
first defined geometry field (by default, the first geometry field is picked).
* ``srid``: The SRID to use for the ``geometry`` content. Defaults to 4326
(WGS 84).
The :ref:`fields <subset-of-fields>` option can be used to limit fields that
will be present in the ``properties`` key, as it works with all other
serializers.
Example::
from django.core.serializers import serialize
from my_app.models import City
serialize('geojson', City.objects.all(),
geometry_field='point',
fields=('name',))
Would output::
{
'type': 'FeatureCollection',
'crs': {
'type': 'name',
'properties': {'name': 'EPSG:4326'}
},
'features': [
{
'type': 'Feature',
'geometry': {
'type': 'Point',
'coordinates': [-87.650175, 41.850385]
},
'properties': {
'name': 'Chicago'
}
}
]
}