1 """

     2  The GDAL/OGR library uses an Envelope structure to hold the bounding

     3  box information for a geometry.  The envelope (bounding box) contains

     4  two pairs of coordinates, one for the lower left coordinate and one

     5  for the upper right coordinate:

     6 

     7                            +----------o Upper right; (max_x, max_y)

     8                            |          |

     9                            |          |

    10                            |          |

    11  Lower left (min_x, min_y) o----------+

    12 """

    13 from ctypes import Structure, c_double

    14 from types import TupleType, ListType

    15 from django.contrib.gis.gdal.error import OGRException

    16 

    17 # The OGR definition of an Envelope is a C structure containing four doubles.

    18 #  See the 'ogr_core.h' source file for more information:

    19 #   http://www.gdal.org/ogr/ogr__core_8h-source.html

    20 class OGREnvelope(Structure):

    21     "Represents the OGREnvelope C Structure."

    22     _fields_ = [("MinX", c_double),

    23                 ("MaxX", c_double),

    24                 ("MinY", c_double),

    25                 ("MaxY", c_double),

    26                 ]

    27 

    28 class Envelope(object):

    29     """

    30     The Envelope object is a C structure that contains the minimum and

    31     maximum X, Y coordinates for a rectangle bounding box.  The naming

    32     of the variables is compatible with the OGR Envelope structure.

    33     """

    34 

    35     def __init__(self, *args):

    36         """

    37         The initialization function may take an OGREnvelope structure, 4-element

    38         tuple or list, or 4 individual arguments.

    39         """

    40         

    41         if len(args) == 1:

    42             if isinstance(args[0], OGREnvelope):

    43                 # OGREnvelope (a ctypes Structure) was passed in.

    44                 self._envelope = args[0]

    45             elif isinstance(args[0], (TupleType, ListType)):

    46                 # A tuple was passed in.

    47                 if len(args[0]) != 4:

    48                     raise OGRException('Incorrect number of tuple elements (%d).' % len(args[0]))

    49                 else:

    50                     self._from_sequence(args[0])

    51             else:

    52                 raise TypeError('Incorrect type of argument: %s' % str(type(args[0])))

    53         elif len(args) == 4:

    54             # Individiual parameters passed in.

    55             #  Thanks to ww for the help

    56             self._from_sequence(map(float, args))

    57         else:

    58             raise OGRException('Incorrect number (%d) of arguments.' % len(args))

    59 

    60         # Checking the x,y coordinates

    61         if self.min_x >= self.max_x:

    62             raise OGRException('Envelope minimum X >= maximum X.')

    63         if self.min_y >= self.max_y:

    64             raise OGRException('Envelope minimum Y >= maximum Y.')

    65 

    66     def __eq__(self, other):

    67         """

    68         Returns True if the envelopes are equivalent; can compare against

    69         other Envelopes and 4-tuples.

    70         """

    71         if isinstance(other, Envelope):

    72             return (self.min_x == other.min_x) and (self.min_y == other.min_y) and \

    73                    (self.max_x == other.max_x) and (self.max_y == other.max_y)

    74         elif isinstance(other, TupleType) and len(other) == 4:

    75             return (self.min_x == other[0]) and (self.min_y == other[1]) and \

    76                    (self.max_x == other[2]) and (self.max_y == other[3])

    77         else:

    78             raise OGRException('Equivalence testing only works with other Envelopes.')

    79 

    80     def __str__(self):

    81         "Returns a string representation of the tuple."

    82         return str(self.tuple)

    83 

    84     def _from_sequence(self, seq):

    85         "Initializes the C OGR Envelope structure from the given sequence."

    86         self._envelope = OGREnvelope()

    87         self._envelope.MinX = seq[0]

    88         self._envelope.MinY = seq[1]

    89         self._envelope.MaxX = seq[2]

    90         self._envelope.MaxY = seq[3]

    91     

    92     @property

    93     def min_x(self):

    94         "Returns the value of the minimum X coordinate."

    95         return self._envelope.MinX

    96 

    97     @property

    98     def min_y(self):

    99         "Returns the value of the minimum Y coordinate."

   100         return self._envelope.MinY

   101 

   102     @property

   103     def max_x(self):

   104         "Returns the value of the maximum X coordinate."

   105         return self._envelope.MaxX

   106 

   107     @property

   108     def max_y(self):

   109         "Returns the value of the maximum Y coordinate."

   110         return self._envelope.MaxY

   111 

   112     @property

   113     def ur(self):

   114         "Returns the upper-right coordinate."

   115         return (self.max_x, self.max_y)

   116 

   117     @property

   118     def ll(self):

   119         "Returns the lower-left coordinate."

   120         return (self.min_x, self.min_y)

   121 

   122     @property

   123     def tuple(self):

   124         "Returns a tuple representing the envelope."

   125         return (self.min_x, self.min_y, self.max_x, self.max_y)

   126 

   127     @property

   128     def wkt(self):

   129         "Returns WKT representing a Polygon for this envelope."

   130         # TODO: Fix significant figures.

   131         return 'POLYGON((%s %s,%s %s,%s %s,%s %s,%s %s))' % \

   132                (self.min_x, self.min_y, self.min_x, self.max_y,

   133                 self.max_x, self.max_y, self.max_x, self.min_y,

   134                 self.min_x, self.min_y)