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Diffstat (limited to 'webapp/django/contrib/gis/gdal/envelope.py')
-rw-r--r-- | webapp/django/contrib/gis/gdal/envelope.py | 134 |
1 files changed, 134 insertions, 0 deletions
diff --git a/webapp/django/contrib/gis/gdal/envelope.py b/webapp/django/contrib/gis/gdal/envelope.py new file mode 100644 index 0000000000..971f06da90 --- /dev/null +++ b/webapp/django/contrib/gis/gdal/envelope.py @@ -0,0 +1,134 @@ +""" + 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) |