| """ |
| 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 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], (tuple, list)): |
| # 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, 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 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] |
| |
| 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 OGRException('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: |
| # Individiual parameters passed in. |
| return self.expand_to_include(args) |
| else: |
| raise OGRException('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) |
