284 lines
10 KiB
Python
284 lines
10 KiB
Python
"""
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Imports the SpatialRefSys and GeometryColumns models dependent on the
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spatial database backend.
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"""
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import re
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from django.conf import settings
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# Checking for the presence of GDAL (needed for the SpatialReference object)
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from django.contrib.gis.gdal import HAS_GDAL, PYTHON23
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if HAS_GDAL:
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from django.contrib.gis.gdal import SpatialReference
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class SpatialRefSysMixin(object):
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"""
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The SpatialRefSysMixin is a class used by the database-dependent
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SpatialRefSys objects to reduce redundnant code.
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"""
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# For pulling out the spheroid from the spatial reference string. This
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# regular expression is used only if the user does not have GDAL installed.
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# TODO: Flattening not used in all ellipsoids, could also be a minor axis, or 'b'
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# parameter.
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spheroid_regex = re.compile(r'.+SPHEROID\[\"(?P<name>.+)\",(?P<major>\d+(\.\d+)?),(?P<flattening>\d{3}\.\d+),')
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# For pulling out the units on platforms w/o GDAL installed.
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# TODO: Figure out how to pull out angular units of projected coordinate system and
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# fix for LOCAL_CS types. GDAL should be highly recommended for performing
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# distance queries.
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units_regex = re.compile(r'.+UNIT ?\["(?P<unit_name>[\w \'\(\)]+)", ?(?P<unit>[\d\.]+)(,AUTHORITY\["(?P<unit_auth_name>[\w \'\(\)]+)","(?P<unit_auth_val>\d+)"\])?\]([\w ]+)?(,AUTHORITY\["(?P<auth_name>[\w \'\(\)]+)","(?P<auth_val>\d+)"\])?\]$')
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def srs(self):
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"""
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Returns a GDAL SpatialReference object, if GDAL is installed.
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"""
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if HAS_GDAL:
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if hasattr(self, '_srs'):
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# Returning a clone of the cached SpatialReference object.
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return self._srs.clone()
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else:
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# Attempting to cache a SpatialReference object.
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# Trying to get from WKT first.
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try:
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self._srs = SpatialReference(self.wkt)
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return self.srs
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except Exception, msg:
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pass
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raise Exception('Could not get OSR SpatialReference from WKT: %s\nError:\n%s' % (self.wkt, msg))
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else:
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raise Exception('GDAL is not installed.')
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srs = property(srs)
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def ellipsoid(self):
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"""
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Returns a tuple of the ellipsoid parameters:
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(semimajor axis, semiminor axis, and inverse flattening).
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"""
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if HAS_GDAL:
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return self.srs.ellipsoid
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else:
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m = self.spheroid_regex.match(self.wkt)
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if m: return (float(m.group('major')), float(m.group('flattening')))
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else: return None
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ellipsoid = property(ellipsoid)
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def name(self):
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"Returns the projection name."
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return self.srs.name
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name = property(name)
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def spheroid(self):
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"Returns the spheroid name for this spatial reference."
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return self.srs['spheroid']
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spheroid = property(spheroid)
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def datum(self):
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"Returns the datum for this spatial reference."
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return self.srs['datum']
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datum = property(datum)
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def projected(self):
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"Is this Spatial Reference projected?"
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if HAS_GDAL:
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return self.srs.projected
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else:
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return self.wkt.startswith('PROJCS')
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projected = property(projected)
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def local(self):
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"Is this Spatial Reference local?"
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if HAS_GDAL:
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return self.srs.local
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else:
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return self.wkt.startswith('LOCAL_CS')
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local = property(local)
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def geographic(self):
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"Is this Spatial Reference geographic?"
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if HAS_GDAL:
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return self.srs.geographic
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else:
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return self.wkt.startswith('GEOGCS')
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geographic = property(geographic)
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def linear_name(self):
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"Returns the linear units name."
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if HAS_GDAL:
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return self.srs.linear_name
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elif self.geographic:
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return None
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else:
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m = self.units_regex.match(self.wkt)
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return m.group('unit_name')
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linear_name = property(linear_name)
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def linear_units(self):
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"Returns the linear units."
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if HAS_GDAL:
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return self.srs.linear_units
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elif self.geographic:
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return None
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else:
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m = self.units_regex.match(self.wkt)
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return m.group('unit')
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linear_units = property(linear_units)
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def angular_name(self):
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"Returns the name of the angular units."
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if HAS_GDAL:
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return self.srs.angular_name
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elif self.projected:
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return None
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else:
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m = self.units_regex.match(self.wkt)
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return m.group('unit_name')
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angular_name = property(angular_name)
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def angular_units(self):
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"Returns the angular units."
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if HAS_GDAL:
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return self.srs.angular_units
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elif self.projected:
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return None
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else:
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m = self.units_regex.match(self.wkt)
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return m.group('unit')
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angular_units = property(angular_units)
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def units(self):
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"Returns a tuple of the units and the name."
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if self.projected or self.local:
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return (self.linear_units, self.linear_name)
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elif self.geographic:
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return (self.angular_units, self.angular_name)
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else:
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return (None, None)
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units = property(units)
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def get_units(cls, wkt):
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"""
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Class method used by GeometryField on initialization to
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retrive the units on the given WKT, without having to use
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any of the database fields.
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"""
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if HAS_GDAL:
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return SpatialReference(wkt).units
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else:
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m = cls.units_regex.match(wkt)
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return m.group('unit'), m.group('unit_name')
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get_units = classmethod(get_units)
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def get_spheroid(cls, wkt, string=True):
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"""
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Class method used by GeometryField on initialization to
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retrieve the `SPHEROID[..]` parameters from the given WKT.
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"""
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if HAS_GDAL:
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srs = SpatialReference(wkt)
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sphere_params = srs.ellipsoid
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sphere_name = srs['spheroid']
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else:
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m = cls.spheroid_regex.match(wkt)
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if m:
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sphere_params = (float(m.group('major')), float(m.group('flattening')))
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sphere_name = m.group('name')
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else:
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return None
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if not string:
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return sphere_name, sphere_params
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else:
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# `string` parameter used to place in format acceptable by PostGIS
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if len(sphere_params) == 3:
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radius, flattening = sphere_params[0], sphere_params[2]
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else:
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radius, flattening = sphere_params
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return 'SPHEROID["%s",%s,%s]' % (sphere_name, radius, flattening)
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get_spheroid = classmethod(get_spheroid)
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def __unicode__(self):
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"""
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Returns the string representation. If GDAL is installed,
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it will be 'pretty' OGC WKT.
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"""
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try:
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return unicode(self.srs)
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except:
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return unicode(self.wkt)
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# The SpatialRefSys and GeometryColumns models
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_srid_info = True
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if not PYTHON23 and settings.DATABASE_ENGINE == 'postgresql_psycopg2':
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# Because the PostGIS version is checked when initializing the spatial
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# backend a `ProgrammingError` will be raised if the PostGIS tables
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# and functions are not installed. We catch here so it won't be raised when
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# running the Django test suite. `ImportError` is also possible if no ctypes.
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try:
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from django.contrib.gis.db.backend.postgis.models import GeometryColumns, SpatialRefSys
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except:
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_srid_info = False
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elif not PYTHON23 and settings.DATABASE_ENGINE == 'oracle':
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# Same thing as above, except the GEOS library is attempted to be loaded for
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# `BaseSpatialBackend`, and an exception will be raised during the
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# Django test suite if it doesn't exist.
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try:
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from django.contrib.gis.db.backend.oracle.models import GeometryColumns, SpatialRefSys
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except:
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_srid_info = False
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else:
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_srid_info = False
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if _srid_info:
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def get_srid_info(srid):
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"""
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Returns the units, unit name, and spheroid WKT associated with the
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given SRID from the `spatial_ref_sys` (or equivalent) spatial database
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table. We use a database cursor to execute the query because this
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function is used when it is not possible to use the ORM (for example,
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during field initialization).
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"""
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# SRID=-1 is a common convention for indicating the geometry has no
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# spatial reference information associated with it. Thus, we will
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# return all None values without raising an exception.
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if srid == -1: return None, None, None
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# Getting the spatial reference WKT associated with the SRID from the
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# `spatial_ref_sys` (or equivalent) spatial database table. This query
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# cannot be executed using the ORM because this information is needed
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# when the ORM cannot be used (e.g., during the initialization of
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# `GeometryField`).
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from django.db import connection
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cur = connection.cursor()
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qn = connection.ops.quote_name
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stmt = 'SELECT %(table)s.%(wkt_col)s FROM %(table)s WHERE (%(table)s.%(srid_col)s = %(srid)s)'
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stmt = stmt % {'table' : qn(SpatialRefSys._meta.db_table),
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'wkt_col' : qn(SpatialRefSys.wkt_col()),
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'srid_col' : qn('srid'),
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'srid' : srid,
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}
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cur.execute(stmt)
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# Fetching the WKT from the cursor; if the query failed raise an Exception.
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fetched = cur.fetchone()
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if not fetched:
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raise ValueError('Failed to find spatial reference entry in "%s" corresponding to SRID=%s.' %
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(SpatialRefSys._meta.db_table, srid))
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srs_wkt = fetched[0]
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# Getting metadata associated with the spatial reference system identifier.
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# Specifically, getting the unit information and spheroid information
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# (both required for distance queries).
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unit, unit_name = SpatialRefSys.get_units(srs_wkt)
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spheroid = SpatialRefSys.get_spheroid(srs_wkt)
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return unit, unit_name, spheroid
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else:
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def get_srid_info(srid):
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"""
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Dummy routine for the backends that do not have the OGC required
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spatial metadata tables (like MySQL).
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"""
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return None, None, None
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