from django.contrib.gis.gdal import SpatialReference
from django.db import connections,DEFAULT_DB_ALIAS
def add_srs_entry(srs, auth_name='EPSG', auth_srid=None, ref_sys_name=None,
database=DEFAULT_DB_ALIAS):
"""
This function takes a GDAL SpatialReference system and adds its information
to the `spatial_ref_sys` table of the spatial backend. Doing this enables
database-level spatial transformations for the backend. Thus, this utility
is useful for adding spatial reference systems not included by default with
the backend -- for example, the so-called "Google Maps Mercator Projection"
is excluded in PostGIS 1.3 and below, and the following adds it to the
`spatial_ref_sys` table:
>>> from django.contrib.gis.utils import add_srs_entry
>>> add_srs_entry(900913)
Keyword Arguments:
auth_name:
This keyword may be customized with the value of the `auth_name` field.
Defaults to 'EPSG'.
auth_srid:
This keyword may be customized with the value of the `auth_srid` field.
Defaults to the SRID determined by GDAL.
ref_sys_name:
For SpatiaLite users only, sets the value of the the `ref_sys_name` field.
Defaults to the name determined by GDAL.
database:
The name of the database connection to use; the default is the value
of `django.db.DEFAULT_DB_ALIAS` (at the time of this writing, it's value
is 'default').
"""
connection = connections[database]
if not hasattr(connection.ops, 'spatial_version'):
raise Exception('The `add_srs_entry` utility only works '
'with spatial backends.')
if connection.ops.oracle or connection.ops.mysql:
raise Exception('This utility does not support the '
'Oracle or MySQL spatial backends.')
SpatialRefSys = connection.ops.spatial_ref_sys()
# If argument is not a `SpatialReference` instance, use it as parameter
# to construct a `SpatialReference` instance.
if not isinstance(srs, SpatialReference):
srs = SpatialReference(srs)
if srs.srid is None:
raise Exception('Spatial reference requires an SRID to be '
'compatible with the spatial backend.')
# Initializing the keyword arguments dictionary for both PostGIS
# and SpatiaLite.
kwargs = {'srid' : srs.srid,
'auth_name' : auth_name,
'auth_srid' : auth_srid or srs.srid,
'proj4text' : srs.proj4,
}
# Backend-specific fields for the SpatialRefSys model.
if connection.ops.postgis:
kwargs['srtext'] = srs.wkt
if connection.ops.spatialite:
kwargs['ref_sys_name'] = ref_sys_name or srs.name
# Creating the spatial_ref_sys model.
try:
# Try getting via SRID only, because using all kwargs may
# differ from exact wkt/proj in database.
sr = SpatialRefSys.objects.get(srid=srs.srid)
except SpatialRefSys.DoesNotExist:
sr = SpatialRefSys.objects.create(**kwargs)
# Alias is for backwards-compatibility purposes.
add_postgis_srs = add_srs_entry
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