django1/django/contrib/gis/models.py

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"""
Imports the SpatialRefSys and GeometryColumns models dependent on the
spatial database backend.
"""
import re
from django.conf import settings
# Checking for the presence of GDAL (needed for the SpatialReference object)
from django.contrib.gis.gdal import HAS_GDAL
if HAS_GDAL:
from django.contrib.gis.gdal import SpatialReference
class SpatialRefSysMixin(object):
"""
The SpatialRefSysMixin is a class used by the database-dependent
SpatialRefSys objects to reduce redundnant code.
"""
# For pulling out the spheroid from the spatial reference string. This
# regular expression is used only if the user does not have GDAL installed.
# TODO: Flattening not used in all ellipsoids, could also be a minor axis, or 'b'
# parameter.
spheroid_regex = re.compile(r'.+SPHEROID\[\"(?P<name>.+)\",(?P<major>\d+(\.\d+)?),(?P<flattening>\d{3}\.\d+),')
# For pulling out the units on platforms w/o GDAL installed.
# TODO: Figure out how to pull out angular units of projected coordinate system and
# fix for LOCAL_CS types. GDAL should be highly recommended for performing
# distance queries.
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+)"\])?\]$')
@property
def srs(self):
"""
Returns a GDAL SpatialReference object, if GDAL is installed.
"""
if HAS_GDAL:
if hasattr(self, '_srs'):
# Returning a clone of the cached SpatialReference object.
return self._srs.clone()
else:
# Attempting to cache a SpatialReference object.
# Trying to get from WKT first.
try:
self._srs = SpatialReference(self.wkt)
return self.srs
except Exception, msg:
pass
raise Exception('Could not get OSR SpatialReference from WKT: %s\nError:\n%s' % (self.wkt, msg))
else:
raise Exception('GDAL is not installed.')
@property
def ellipsoid(self):
"""
Returns a tuple of the ellipsoid parameters:
(semimajor axis, semiminor axis, and inverse flattening).
"""
if HAS_GDAL:
return self.srs.ellipsoid
else:
m = self.spheroid_regex.match(self.wkt)
if m: return (float(m.group('major')), float(m.group('flattening')))
else: return None
@property
def name(self):
"Returns the projection name."
return self.srs.name
@property
def spheroid(self):
"Returns the spheroid name for this spatial reference."
return self.srs['spheroid']
@property
def datum(self):
"Returns the datum for this spatial reference."
return self.srs['datum']
@property
def projected(self):
"Is this Spatial Reference projected?"
if HAS_GDAL:
return self.srs.projected
else:
return self.wkt.startswith('PROJCS')
@property
def local(self):
"Is this Spatial Reference local?"
if HAS_GDAL:
return self.srs.local
else:
return self.wkt.startswith('LOCAL_CS')
@property
def geographic(self):
"Is this Spatial Reference geographic?"
if HAS_GDAL:
return self.srs.geographic
else:
return self.wkt.startswith('GEOGCS')
@property
def linear_name(self):
"Returns the linear units name."
if HAS_GDAL:
return self.srs.linear_name
elif self.geographic:
return None
else:
m = self.units_regex.match(self.wkt)
return m.group('unit_name')
@property
def linear_units(self):
"Returns the linear units."
if HAS_GDAL:
return self.srs.linear_units
elif self.geographic:
return None
else:
m = self.units_regex.match(self.wkt)
return m.group('unit')
@property
def angular_name(self):
"Returns the name of the angular units."
if HAS_GDAL:
return self.srs.angular_name
elif self.projected:
return None
else:
m = self.units_regex.match(self.wkt)
return m.group('unit_name')
@property
def angular_units(self):
"Returns the angular units."
if HAS_GDAL:
return self.srs.angular_units
elif self.projected:
return None
else:
m = self.units_regex.match(self.wkt)
return m.group('unit')
@property
def units(self):
"Returns a tuple of the units and the name."
if self.projected or self.local:
return (self.linear_units, self.linear_name)
elif self.geographic:
return (self.angular_units, self.angular_name)
else:
return (None, None)
@classmethod
def get_units(cls, wkt):
"""
Class method used by GeometryField on initialization to
retrive the units on the given WKT, without having to use
any of the database fields.
"""
if HAS_GDAL:
return SpatialReference(wkt).units
else:
m = cls.units_regex.match(wkt)
return m.group('unit'), m.group('unit_name')
@classmethod
def get_spheroid(cls, wkt, string=True):
"""
Class method used by GeometryField on initialization to
retrieve the `SPHEROID[..]` parameters from the given WKT.
"""
if HAS_GDAL:
srs = SpatialReference(wkt)
sphere_params = srs.ellipsoid
sphere_name = srs['spheroid']
else:
m = cls.spheroid_regex.match(wkt)
if m:
sphere_params = (float(m.group('major')), float(m.group('flattening')))
sphere_name = m.group('name')
else:
return None
if not string:
return sphere_name, sphere_params
else:
# `string` parameter used to place in format acceptable by PostGIS
if len(sphere_params) == 3:
radius, flattening = sphere_params[0], sphere_params[2]
else:
radius, flattening = sphere_params
return 'SPHEROID["%s",%s,%s]' % (sphere_name, radius, flattening)
def __unicode__(self):
"""
Returns the string representation. If GDAL is installed,
it will be 'pretty' OGC WKT.
"""
try:
return unicode(self.srs)
except:
return unicode(self.wkt)
# The SpatialRefSys and GeometryColumns models
_srid_info = True
if settings.DATABASE_ENGINE == 'postgresql_psycopg2':
# Because the PostGIS version is checked when initializing the spatial
# backend a `ProgrammingError` will be raised if the PostGIS tables
# and functions are not installed. We catch here so it won't be raised when
# running the Django test suite.
from psycopg2 import ProgrammingError
try:
from django.contrib.gis.db.backend.postgis.models import GeometryColumns, SpatialRefSys
except ProgrammingError:
_srid_info = False
elif settings.DATABASE_ENGINE == 'oracle':
# Same thing as above, except the GEOS library is attempted to be loaded for
# `BaseSpatialBackend`, and an exception will be raised during the
# Django test suite if it doesn't exist.
try:
from django.contrib.gis.db.backend.oracle.models import GeometryColumns, SpatialRefSys
except:
_srid_info = False
else:
_srid_info = False
if _srid_info:
def get_srid_info(srid):
"""
Returns the units, unit name, and spheroid WKT associated with the
given SRID from the `spatial_ref_sys` (or equivalent) spatial database
table. We use a database cursor to execute the query because this
function is used when it is not possible to use the ORM (for example,
during field initialization).
"""
# SRID=-1 is a common convention for indicating the geometry has no
# spatial reference information associated with it. Thus, we will
# return all None values without raising an exception.
if srid == -1: return None, None, None
# Getting the spatial reference WKT associated with the SRID from the
# `spatial_ref_sys` (or equivalent) spatial database table. This query
# cannot be executed using the ORM because this information is needed
# when the ORM cannot be used (e.g., during the initialization of
# `GeometryField`).
from django.db import connection
cur = connection.cursor()
qn = connection.ops.quote_name
stmt = 'SELECT %(table)s.%(wkt_col)s FROM %(table)s WHERE (%(table)s.%(srid_col)s = %(srid)s)'
stmt = stmt % {'table' : qn(SpatialRefSys._meta.db_table),
'wkt_col' : qn(SpatialRefSys.wkt_col()),
'srid_col' : qn('srid'),
'srid' : srid,
}
cur.execute(stmt)
# Fetching the WKT from the cursor; if the query failed raise an Exception.
fetched = cur.fetchone()
if not fetched:
raise ValueError('Failed to find spatial reference entry in "%s" corresponding to SRID=%s.' %
(SpatialRefSys._meta.db_table, srid))
srs_wkt = fetched[0]
# Getting metadata associated with the spatial reference system identifier.
# Specifically, getting the unit information and spheroid information
# (both required for distance queries).
unit, unit_name = SpatialRefSys.get_units(srs_wkt)
spheroid = SpatialRefSys.get_spheroid(srs_wkt)
return unit, unit_name, spheroid
else:
def get_srid_info(srid):
"""
Dummy routine for the backends that do not have the OGC required
spatial metadata tables (like MySQL).
"""
return None, None, None