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from django.contrib.gis import gdal
class SpatialRefSysMixin:
"""
The SpatialRefSysMixin is a class used by the database-dependent
SpatialRefSys objects to reduce redundant code.
"""
@property
def srs(self):
"""
Return a GDAL SpatialReference object.
"""
# TODO: Is caching really necessary here? Is complexity worth it?
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 = gdal.SpatialReference(self.wkt)
return self.srs
except Exception as e:
msg = e
try:
self._srs = gdal.SpatialReference(self.proj4text)
return self.srs
except Exception as e:
msg = e
raise Exception(
"Could not get OSR SpatialReference from WKT: %s\nError:\n%s"
% (self.wkt, msg)
)
@property
def ellipsoid(self):
"""
Return a tuple of the ellipsoid parameters:
(semimajor axis, semiminor axis, and inverse flattening).
"""
return self.srs.ellipsoid
@property
def name(self):
"Return the projection name."
return self.srs.name
@property
def spheroid(self):
"Return the spheroid name for this spatial reference."
return self.srs["spheroid"]
@property
def datum(self):
"Return the datum for this spatial reference."
return self.srs["datum"]
@property
def projected(self):
"Is this Spatial Reference projected?"
return self.srs.projected
@property
def local(self):
"Is this Spatial Reference local?"
return self.srs.local
@property
def geographic(self):
"Is this Spatial Reference geographic?"
return self.srs.geographic
@property
def linear_name(self):
"Return the linear units name."
return self.srs.linear_name
@property
def linear_units(self):
"Return the linear units."
return self.srs.linear_units
@property
def angular_name(self):
"Return the name of the angular units."
return self.srs.angular_name
@property
def angular_units(self):
"Return the angular units."
return self.srs.angular_units
@property
def units(self):
"Return 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):
"""
Return a tuple of (unit_value, unit_name) for the given WKT without
using any of the database fields.
"""
return gdal.SpatialReference(wkt).units
@classmethod
def get_spheroid(cls, wkt, string=True):
"""
Class method used by GeometryField on initialization to
retrieve the `SPHEROID[..]` parameters from the given WKT.
"""
srs = gdal.SpatialReference(wkt)
sphere_params = srs.ellipsoid
sphere_name = srs["spheroid"]
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 __str__(self):
"""
Return the string representation, a 'pretty' OGC WKT.
"""
return str(self.srs)
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