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