140 lines
4.0 KiB
Python
140 lines
4.0 KiB
Python
from django.contrib.gis import gdal
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from django.utils import six
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from django.utils.encoding import python_2_unicode_compatible
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@python_2_unicode_compatible
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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 redundant code.
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"""
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@property
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def srs(self):
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"""
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Returns a GDAL SpatialReference object.
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"""
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# TODO: Is caching really necessary here? Is complexity worth it?
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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 = gdal.SpatialReference(self.wkt)
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return self.srs
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except Exception as e:
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msg = e
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try:
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self._srs = gdal.SpatialReference(self.proj4text)
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return self.srs
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except Exception as e:
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msg = e
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raise Exception('Could not get OSR SpatialReference from WKT: %s\nError:\n%s' % (self.wkt, msg))
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@property
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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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return self.srs.ellipsoid
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@property
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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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@property
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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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@property
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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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@property
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def projected(self):
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"Is this Spatial Reference projected?"
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return self.srs.projected
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@property
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def local(self):
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"Is this Spatial Reference local?"
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return self.srs.local
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@property
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def geographic(self):
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"Is this Spatial Reference geographic?"
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return self.srs.geographic
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@property
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def linear_name(self):
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"Returns the linear units name."
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return self.srs.linear_name
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@property
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def linear_units(self):
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"Returns the linear units."
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return self.srs.linear_units
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@property
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def angular_name(self):
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"Returns the name of the angular units."
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return self.srs.angular_name
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@property
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def angular_units(self):
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"Returns the angular units."
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return self.srs.angular_units
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@property
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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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@classmethod
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def get_units(cls, wkt):
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"""
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Return a tuple of (unit_value, unit_name) for the given WKT without
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using any of the database fields.
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"""
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return gdal.SpatialReference(wkt).units
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@classmethod
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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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srs = gdal.SpatialReference(wkt)
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sphere_params = srs.ellipsoid
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sphere_name = srs['spheroid']
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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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def __str__(self):
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"""
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Returns the string representation, a 'pretty' OGC WKT.
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"""
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return six.text_type(self.srs)
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