base.py

"""
Base/mixin classes for the spatial backend database operations and the
`SpatialRefSys` model the backend.
"""
import re
from django.contrib.gis import gdal
from django.utils import six
from django.utils.encoding import python_2_unicode_compatible

class BaseSpatialOperations(object):
    """
    This module holds the base `BaseSpatialBackend` object, which is
    instantiated by each spatial database backend with the features
    it has.
    """
    distance_functions = {}
    geometry_functions = {}
    geometry_operators = {}
    geography_operators = {}
    geography_functions = {}
    gis_terms = {}
    truncate_params = {}

    # Quick booleans for the type of this spatial backend, and
    # an attribute for the spatial database version tuple (if applicable)
    postgis = False
    spatialite = False
    mysql = False
    oracle = False
    spatial_version = None

    # How the geometry column should be selected.
    select = None

    # Does the spatial database have a geography type?
    geography = False

    area = False
    centroid = False
    difference = False
    distance = False
    distance_sphere = False
    distance_spheroid = False
    envelope = False
    force_rhr = False
    mem_size = False
    bounding_circle = False
    num_geom = False
    num_points = False
    perimeter = False
    perimeter3d = False
    point_on_surface = False
    polygonize = False
    reverse = False
    scale = False
    snap_to_grid = False
    sym_difference = False
    transform = False
    translate = False
    union = False

    # Aggregates
    collect = False
    extent = False
    extent3d = False
    make_line = False
    unionagg = False

    # Serialization
    geohash = False
    geojson = False
    gml = False
    kml = False
    svg = False

    # Constructors
    from_text = False
    from_wkb = False

    # Default conversion functions for aggregates; will be overridden if implemented
    # for the spatial backend.
    def convert_extent(self, box):
        raise NotImplementedError('Aggregate extent not implemented for this spatial backend.')

    def convert_extent3d(self, box):
        raise NotImplementedError('Aggregate 3D extent not implemented for this spatial backend.')

    def convert_geom(self, geom_val, geom_field):
        raise NotImplementedError('Aggregate method not implemented for this spatial backend.')

    # For quoting column values, rather than columns.
    def geo_quote_name(self, name):
        return "'%s'" % name

    # GeometryField operations
    def geo_db_type(self, f):
        """
        Returns the database column type for the geometry field on
        the spatial backend.
        """
        raise NotImplementedError

    def get_distance(self, f, value, lookup_type):
        """
        Returns the distance parameters for the given geometry field,
        lookup value, and lookup type.
        """
        raise NotImplementedError('Distance operations not available on this spatial backend.')

    def get_geom_placeholder(self, f, value):
        """
        Returns the placeholder for the given geometry field with the given
        value.  Depending on the spatial backend, the placeholder may contain a
        stored procedure call to the transformation function of the spatial
        backend.
        """
        raise NotImplementedError

    def get_expression_column(self, evaluator):
        """
        Helper method to return the quoted column string from the evaluator
        for its expression.
        """
        for expr, col_tup in evaluator.cols:
            if expr is evaluator.expression:
                return '%s.%s' % tuple(map(self.quote_name, col_tup))
        raise Exception("Could not find the column for the expression.")

    # Spatial SQL Construction
    def spatial_aggregate_sql(self, agg):
        raise NotImplementedError('Aggregate support not implemented for this spatial backend.')

    def spatial_lookup_sql(self, lvalue, lookup_type, value, field):
        raise NotImplementedError

    # Routines for getting the OGC-compliant models.
    def geometry_columns(self):
        raise NotImplementedError

    def spatial_ref_sys(self):
        raise NotImplementedError

@python_2_unicode_compatible
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 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
        retrive 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:
            return six.text_type(self.wkt)