1 from django.contrib.gis.gdal import SpatialReference

     2 from django.db import connections, DEFAULT_DB_ALIAS

     3 

     4 def add_srs_entry(srs, auth_name='EPSG', auth_srid=None, ref_sys_name=None,

     5                   database=DEFAULT_DB_ALIAS):

     6     """

     7     This function takes a GDAL SpatialReference system and adds its information

     8     to the `spatial_ref_sys` table of the spatial backend.  Doing this enables

     9     database-level spatial transformations for the backend.  Thus, this utility

    10     is useful for adding spatial reference systems not included by default with

    11     the backend -- for example, the so-called "Google Maps Mercator Projection"

    12     is excluded in PostGIS 1.3 and below, and the following adds it to the

    13     `spatial_ref_sys` table:

    14 

    15     >>> from django.contrib.gis.utils import add_srs_entry

    16     >>> add_srs_entry(900913)

    17 

    18     Keyword Arguments:

    19      auth_name:

    20        This keyword may be customized with the value of the `auth_name` field.

    21        Defaults to 'EPSG'.

    22 

    23      auth_srid:

    24        This keyword may be customized with the value of the `auth_srid` field.

    25        Defaults to the SRID determined by GDAL.

    26 

    27      ref_sys_name:

    28        For SpatiaLite users only, sets the value of the the `ref_sys_name` field.

    29        Defaults to the name determined by GDAL.

    30 

    31      database:

    32       The name of the database connection to use; the default is the value

    33       of `django.db.DEFAULT_DB_ALIAS` (at the time of this writing, it's value

    34       is 'default').

    35     """

    36     connection = connections[database]

    37     if not hasattr(connection.ops, 'spatial_version'):

    38         raise Exception('The `add_srs_entry` utility only works '

    39                         'with spatial backends.')

    40     if connection.ops.oracle or connection.ops.mysql:

    41         raise Exception('This utility does not support the '

    42                         'Oracle or MySQL spatial backends.')

    43     SpatialRefSys = connection.ops.spatial_ref_sys()

    44 

    45     # If argument is not a `SpatialReference` instance, use it as parameter

    46     # to construct a `SpatialReference` instance.

    47     if not isinstance(srs, SpatialReference):

    48         srs = SpatialReference(srs)

    49 

    50     if srs.srid is None:

    51         raise Exception('Spatial reference requires an SRID to be '

    52                         'compatible with the spatial backend.')

    53 

    54     # Initializing the keyword arguments dictionary for both PostGIS

    55     # and SpatiaLite.

    56     kwargs = {'srid' : srs.srid,

    57               'auth_name' : auth_name,

    58               'auth_srid' : auth_srid or srs.srid,

    59               'proj4text' : srs.proj4,

    60               }

    61 

    62     # Backend-specific fields for the SpatialRefSys model.

    63     if connection.ops.postgis:

    64         kwargs['srtext'] = srs.wkt

    65     if connection.ops.spatialite:

    66         kwargs['ref_sys_name'] = ref_sys_name or srs.name

    67 

    68     # Creating the spatial_ref_sys model.

    69     try:

    70         # Try getting via SRID only, because using all kwargs may

    71         # differ from exact wkt/proj in database.

    72         sr = SpatialRefSys.objects.get(srid=srs.srid)

    73     except SpatialRefSys.DoesNotExist:

    74         sr = SpatialRefSys.objects.create(**kwargs)

    75 

    76 # Alias is for backwards-compatibility purposes.

    77 add_postgis_srs = add_srs_entry