+
−"""
+
− The GDAL/OGR library uses an Envelope structure to hold the bounding
+
− box information for a geometry.  The envelope (bounding box) contains
+
− two pairs of coordinates, one for the lower left coordinate and one
+
− for the upper right coordinate:
+
−
+
−                           +----------o Upper right; (max_x, max_y)
+
−                           |          |
+
−                           |          |
+
−                           |          |
+
− Lower left (min_x, min_y) o----------+
+
−"""
+
−from ctypes import Structure, c_double
+
−from types import TupleType, ListType
+
−from django.contrib.gis.gdal.error import OGRException
+
−
+
−# The OGR definition of an Envelope is a C structure containing four doubles.
+
−#  See the 'ogr_core.h' source file for more information:
+
−#   http://www.gdal.org/ogr/ogr__core_8h-source.html
+
−class OGREnvelope(Structure):
+
−    "Represents the OGREnvelope C Structure."
+
−    _fields_ = [("MinX", c_double),
+
−                ("MaxX", c_double),
+
−                ("MinY", c_double),
+
−                ("MaxY", c_double),
+
−                ]
+
−
+
−class Envelope(object):
+
−    """
+
−    The Envelope object is a C structure that contains the minimum and
+
−    maximum X, Y coordinates for a rectangle bounding box.  The naming
+
−    of the variables is compatible with the OGR Envelope structure.
+
−    """
+
−
+
−    def __init__(self, *args):
+
−        """
+
−        The initialization function may take an OGREnvelope structure, 4-element
+
−        tuple or list, or 4 individual arguments.
+
−        """
+
−        
+
−        if len(args) == 1:
+
−            if isinstance(args[0], OGREnvelope):
+
−                # OGREnvelope (a ctypes Structure) was passed in.
+
−                self._envelope = args[0]
+
−            elif isinstance(args[0], (TupleType, ListType)):
+
−                # A tuple was passed in.
+
−                if len(args[0]) != 4:
+
−                    raise OGRException('Incorrect number of tuple elements (%d).' % len(args[0]))
+
−                else:
+
−                    self._from_sequence(args[0])
+
−            else:
+
−                raise TypeError('Incorrect type of argument: %s' % str(type(args[0])))
+
−        elif len(args) == 4:
+
−            # Individiual parameters passed in.
+
−            #  Thanks to ww for the help
+
−            self._from_sequence(map(float, args))
+
−        else:
+
−            raise OGRException('Incorrect number (%d) of arguments.' % len(args))
+
−
+
−        # Checking the x,y coordinates
+
−        if self.min_x >= self.max_x:
+
−            raise OGRException('Envelope minimum X >= maximum X.')
+
−        if self.min_y >= self.max_y:
+
−            raise OGRException('Envelope minimum Y >= maximum Y.')
+
−
+
−    def __eq__(self, other):
+
−        """
+
−        Returns True if the envelopes are equivalent; can compare against
+
−        other Envelopes and 4-tuples.
+
−        """
+
−        if isinstance(other, Envelope):
+
−            return (self.min_x == other.min_x) and (self.min_y == other.min_y) and \
+
−                   (self.max_x == other.max_x) and (self.max_y == other.max_y)
+
−        elif isinstance(other, TupleType) and len(other) == 4:
+
−            return (self.min_x == other[0]) and (self.min_y == other[1]) and \
+
−                   (self.max_x == other[2]) and (self.max_y == other[3])
+
−        else:
+
−            raise OGRException('Equivalence testing only works with other Envelopes.')
+
−
+
−    def __str__(self):
+
−        "Returns a string representation of the tuple."
+
−        return str(self.tuple)
+
−
+
−    def _from_sequence(self, seq):
+
−        "Initializes the C OGR Envelope structure from the given sequence."
+
−        self._envelope = OGREnvelope()
+
−        self._envelope.MinX = seq[0]
+
−        self._envelope.MinY = seq[1]
+
−        self._envelope.MaxX = seq[2]
+
−        self._envelope.MaxY = seq[3]
+
−    
+
−    @property
+
−    def min_x(self):
+
−        "Returns the value of the minimum X coordinate."
+
−        return self._envelope.MinX
+
−
+
−    @property
+
−    def min_y(self):
+
−        "Returns the value of the minimum Y coordinate."
+
−        return self._envelope.MinY
+
−
+
−    @property
+
−    def max_x(self):
+
−        "Returns the value of the maximum X coordinate."
+
−        return self._envelope.MaxX
+
−
+
−    @property
+
−    def max_y(self):
+
−        "Returns the value of the maximum Y coordinate."
+
−        return self._envelope.MaxY
+
−
+
−    @property
+
−    def ur(self):
+
−        "Returns the upper-right coordinate."
+
−        return (self.max_x, self.max_y)
+
−
+
−    @property
+
−    def ll(self):
+
−        "Returns the lower-left coordinate."
+
−        return (self.min_x, self.min_y)
+
−
+
−    @property
+
−    def tuple(self):
+
−        "Returns a tuple representing the envelope."
+
−        return (self.min_x, self.min_y, self.max_x, self.max_y)
+
−
+
−    @property
+
−    def wkt(self):
+
−        "Returns WKT representing a Polygon for this envelope."
+
−        # TODO: Fix significant figures.
+
−        return 'POLYGON((%s %s,%s %s,%s %s,%s %s,%s %s))' % \
+
−               (self.min_x, self.min_y, self.min_x, self.max_y,
+
−                self.max_x, self.max_y, self.max_x, self.min_y,
+
−                self.min_x, self.min_y)