import re from django.contrib.gis import gdal from django.utils import six from django.utils.encoding import python_2_unicode_compatible @python_2_unicode_compatible class SpatialRefSysMixin(object): """ The SpatialRefSysMixin is a class used by the database-dependent SpatialRefSys objects to reduce redundant 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\.]+)' r'(,AUTHORITY\["(?P<unit_auth_name>[\w \'\(\)]+)",' r'"(?P<unit_auth_val>\d+)"\])?\]([\w ]+)?(,' r'AUTHORITY\["(?P<auth_name>[\w \'\(\)]+)","(?P<auth_val>\d+)"\])?\]$' ) @property def srs(self): """ Returns a GDAL SpatialReference object, if GDAL is installed. """ if gdal.HAS_GDAL: # 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 msg: pass try: self._srs = gdal.SpatialReference(self.proj4text) return self.srs except Exception as 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 gdal.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 gdal.HAS_GDAL: return self.srs.projected else: return self.wkt.startswith('PROJCS') @property def local(self): "Is this Spatial Reference local?" if gdal.HAS_GDAL: return self.srs.local else: return self.wkt.startswith('LOCAL_CS') @property def geographic(self): "Is this Spatial Reference geographic?" if gdal.HAS_GDAL: return self.srs.geographic else: return self.wkt.startswith('GEOGCS') @property def linear_name(self): "Returns the linear units name." if gdal.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 gdal.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 gdal.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 gdal.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 retrieve the units on the given WKT, without having to use any of the database fields. """ if gdal.HAS_GDAL: return gdal.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 gdal.HAS_GDAL: srs = gdal.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 __str__(self): """ Returns the string representation. If GDAL is installed, it will be 'pretty' OGC WKT. """ try: return six.text_type(self.srs) except Exception: return six.text_type(self.wkt)