app/django/contrib/gis/models.py
author Mario Ferraro <fadinlight@gmail.com>
Sun, 15 Nov 2009 22:12:20 +0100
changeset 3093 d1be59b6b627
parent 323 ff1a9aa48cfd
permissions -rw-r--r--
GMaps related JS changed to use new google namespace. Google is going to change permanently in the future the way to load its services, so better stay safe. Also this commit shows uses of the new melange.js module. Fixes Issue 634.

"""
 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, PYTHON23
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+)"\])?\]$')
    
    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.')
    srs = property(srs)

    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
    ellipsoid = property(ellipsoid)

    def name(self):
        "Returns the projection name."
        return self.srs.name
    name = property(name)

    def spheroid(self):
        "Returns the spheroid name for this spatial reference."
        return self.srs['spheroid']
    spheroid = property(spheroid)

    def datum(self):
        "Returns the datum for this spatial reference."
        return self.srs['datum']
    datum = property(datum)

    def projected(self):
        "Is this Spatial Reference projected?"
        if HAS_GDAL:
            return self.srs.projected
        else:
            return self.wkt.startswith('PROJCS')
    projected = property(projected)

    def local(self):
        "Is this Spatial Reference local?"
        if HAS_GDAL:
            return self.srs.local
        else:
            return self.wkt.startswith('LOCAL_CS')
    local = property(local)

    def geographic(self):
        "Is this Spatial Reference geographic?"
        if HAS_GDAL:
            return self.srs.geographic
        else:
            return self.wkt.startswith('GEOGCS')
    geographic = property(geographic)

    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')
    linear_name = property(linear_name)

    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')
    linear_units = property(linear_units)

    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')
    angular_name = property(angular_name)

    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')
    angular_units = property(angular_units)

    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)
    units = property(units)

    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')
    get_units = classmethod(get_units)

    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) 
    get_spheroid = classmethod(get_spheroid)

    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 not PYTHON23 and 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.  `ImportError` is also possible if no ctypes.
    try:
        from django.contrib.gis.db.backend.postgis.models import GeometryColumns, SpatialRefSys
    except:
        _srid_info = False
elif not PYTHON23 and 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