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Source code for django.contrib.gis.gdal.envelope

"""
 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 django.contrib.gis.gdal.error import GDALException


# 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),
                ]


[docs]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], (tuple, list)): # A tuple was passed in. if len(args[0]) != 4: raise GDALException('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: # Individual parameters passed in. # Thanks to ww for the help self._from_sequence([float(a) for a in args]) else: raise GDALException('Incorrect number (%d) of arguments.' % len(args)) # Checking the x,y coordinates if self.min_x > self.max_x: raise GDALException('Envelope minimum X > maximum X.') if self.min_y > self.max_y: raise GDALException('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, tuple) 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 GDALException('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]
[docs] def expand_to_include(self, *args): """ Modifies the envelope to expand to include the boundaries of the passed-in 2-tuple (a point), 4-tuple (an extent) or envelope. """ # We provide a number of different signatures for this method, # and the logic here is all about converting them into a # 4-tuple single parameter which does the actual work of # expanding the envelope. if len(args) == 1: if isinstance(args[0], Envelope): return self.expand_to_include(args[0].tuple) elif hasattr(args[0], 'x') and hasattr(args[0], 'y'): return self.expand_to_include(args[0].x, args[0].y, args[0].x, args[0].y) elif isinstance(args[0], (tuple, list)): # A tuple was passed in. if len(args[0]) == 2: return self.expand_to_include((args[0][0], args[0][1], args[0][0], args[0][1])) elif len(args[0]) == 4: (minx, miny, maxx, maxy) = args[0] if minx < self._envelope.MinX: self._envelope.MinX = minx if miny < self._envelope.MinY: self._envelope.MinY = miny if maxx > self._envelope.MaxX: self._envelope.MaxX = maxx if maxy > self._envelope.MaxY: self._envelope.MaxY = maxy else: raise GDALException('Incorrect number of tuple elements (%d).' % len(args[0])) else: raise TypeError('Incorrect type of argument: %s' % str(type(args[0]))) elif len(args) == 2: # An x and an y parameter were passed in return self.expand_to_include((args[0], args[1], args[0], args[1])) elif len(args) == 4: # Individual parameters passed in. return self.expand_to_include(args) else: raise GDALException('Incorrect number (%d) of arguments.' % len(args[0]))
@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)
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