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__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)
