python-shapely 1.2.14-1 / usr / share / pyshared / shapely / geometry / point.py

"""Points and related utilities
"""

from ctypes import c_double
from ctypes import cast, POINTER

from shapely.geos import lgeos, DimensionError
from shapely.geometry.base import BaseGeometry
from shapely.geometry.proxy import CachingGeometryProxy

__all__ = ['Point', 'asPoint']


class Point(BaseGeometry):
    """
    A zero dimensional feature

    A point has zero length and zero area. 
    
    Attributes
    ----------
    x, y, z : float
        Coordinate values

    Example
    -------
    
      >>> p = Point(1.0, -1.0)
      >>> print p
      POINT (1.0000000000000000 -1.0000000000000000)
      >>> p.y
      -1.0
      >>> p.x
      1.0
    """

    def __init__(self, *args):
        """
        Parameters
        ----------
        There are 2 cases:

        1) 1 parameter: this must satisfy the numpy array protocol.
        2) 2 or more parameters: x, y, z : float
            Easting, northing, and elevation.
        """
        BaseGeometry.__init__(self)
        if len(args) > 0:
            self._set_coords(*args)

    # Coordinate getters and setters

    @property
    def x(self):
        """Return x coordinate."""
        return self.coords[0][0]
    
    @property
    def y(self):
        """Return y coordinate."""
        return self.coords[0][1]
    
    @property
    def z(self):
        """Return z coordinate."""
        if self._ndim != 3:
            raise DimensionError("This point has no z coordinate.")
        return self.coords[0][2]
    
    @property
    def __geo_interface__(self):
        return {
            'type': 'Point',
            'coordinates': self.coords[0]
            }

    @property
    def ctypes(self):
        if not self._ctypes_data:
            array_type = c_double * self._ndim
            array = array_type()
            xy = self.coords[0]
            array[0] = xy[0]
            array[1] = xy[1]
            if self._ndim == 3:
                array[2] = xy[2]
            self._ctypes_data = array
        return self._ctypes_data

    def array_interface(self):
        """Provide the Numpy array protocol."""
        ai = self.array_interface_base
        ai.update({'shape': (self._ndim,)})
        return ai
    __array_interface__ = property(array_interface)

    @property
    def bounds(self):
        xy = self.coords[0]
        return (xy[0], xy[1], xy[0], xy[1])

    # Coordinate access

    def _set_coords(self, *args):
        self.empty()
        if len(args) == 1:
            self._geom, self._ndim = geos_point_from_py(args[0])
        else:
            self._geom, self._ndim = geos_point_from_py(tuple(args))

    coords = property(BaseGeometry._get_coords, _set_coords)

    @property
    def xy(self):
        """Separate arrays of X and Y coordinate values
        
        Example:
        
          >>> x, y = Point(0, 0).xy
          >>> list(x)
          [0.0]
          >>> list(y)
          [0.0]
        """
        return self.coords.xy


class PointAdapter(CachingGeometryProxy, Point):

    _owned = False

    def __init__(self, context):
        self.context = context
        self.factory = geos_point_from_py

    @property
    def _ndim(self):
        try:
            # From array protocol
            array = self.context.__array_interface__
            n = array['shape'][0]
            assert n == 2 or n == 3
            return n
        except AttributeError:
            # Fall back on list
            return len(self.context)

    @property
    def __array_interface__(self):
        """Provide the Numpy array protocol."""
        try:
            return self.context.__array_interface__
        except AttributeError:
            return self.array_interface()

    _get_coords = BaseGeometry._get_coords

    def _set_coords(self, ob):
        raise NotImplementedError("Adapters can not modify their sources")

    coords = property(_get_coords)


def asPoint(context):
    """Adapt an object to the Point interface"""
    return PointAdapter(context)


def geos_point_from_py(ob, update_geom=None, update_ndim=0):
    """Create a GEOS geom from an object that is a coordinate sequence
    or that provides the array interface.

    Returns the GEOS geometry and the number of its dimensions.
    """
    try:
        # From array protocol
        array = ob.__array_interface__
        assert len(array['shape']) == 1
        n = array['shape'][0]
        assert n == 2 or n == 3

        dz = None
        da = array['data']
        if type(da) == type((0,)):
            cdata = da[0]
            cp = cast(cdata, POINTER(c_double))
            dx = c_double(cp[0])
            dy = c_double(cp[1])
            if n == 3:
                dz = c_double(cp[2])
                ndim = 3
        else:
            dx, dy = da[0:2]
            if n == 3:
                dz = da[2]
                ndim = 3

    except AttributeError:
        # Fall back on the case of Python sequence data
        # Accept either (x, y) or [(x, y)]
        if type(ob[0]) == type(tuple()):
            coords = ob[0]
        else:
            coords = ob
        n = len(coords)
        dx = c_double(coords[0])
        dy = c_double(coords[1])
        dz = None
        if n == 3:
            dz = c_double(coords[2])

    if update_geom:
        cs = lgeos.GEOSGeom_getCoordSeq(update_geom)
        if n != update_ndim:
            raise ValueError(
            "Wrong coordinate dimensions; this geometry has dimensions: %d" \
            % update_ndim)
    else:
        cs = lgeos.GEOSCoordSeq_create(1, n)
    
    # Because of a bug in the GEOS C API, always set X before Y
    lgeos.GEOSCoordSeq_setX(cs, 0, dx)
    lgeos.GEOSCoordSeq_setY(cs, 0, dy)
    if n == 3:
        lgeos.GEOSCoordSeq_setZ(cs, 0, dz)
   
    if update_geom:
        return None
    else:
        return lgeos.GEOSGeom_createPoint(cs), n

def update_point_from_py(geom, ob):
    geos_point_from_py(ob, geom._geom, geom._ndim)

# Test runner
def _test():
    import doctest
    doctest.testmod()

if __name__ == "__main__":
    _test()