Function transform

shapely/ops.py:210–282

Apply `func` to all coordinates of `geom`. Returns a new geometry of the same type from the transformed coordinates. `func` maps x, y, and optionally z to output xp, yp, zp. The input parameters may iterable types like lists or arrays or single values. The output shall be of the sa

(func, geom)

def transform(func, geom):
    """Apply `func` to all coordinates of `geom`.

    Returns a new geometry of the same type from the transformed coordinates.

    `func` maps x, y, and optionally z to output xp, yp, zp. The input
    parameters may iterable types like lists or arrays or single values.
    The output shall be of the same type. Scalars in, scalars out.
    Lists in, lists out.

    For example, here is an identity function applicable to both types
    of input.

      def id_func(x, y, z=None):
          return tuple(filter(None, [x, y, z]))

      g2 = transform(id_func, g1)

    Using pyproj >= 2.1, this example will accurately project Shapely geometries:

      import pyproj

      wgs84 = pyproj.CRS('EPSG:4326')
      utm = pyproj.CRS('EPSG:32618')

      project = pyproj.Transformer.from_crs(wgs84, utm, always_xy=True).transform

      g2 = transform(project, g1)

    Note that the always_xy kwarg is required here as Shapely geometries only support
    X,Y coordinate ordering.

    Lambda expressions such as the one in

      g2 = transform(lambda x, y, z=None: (x+1.0, y+1.0), g1)

    also satisfy the requirements for `func`.
    """
    if geom.is_empty:
        return geom
    if geom.geom_type in ("Point", "LineString", "LinearRing", "Polygon"):
        # First we try to apply func to x, y, z sequences. When func is
        # optimized for sequences, this is the fastest, though zipping
        # the results up to go back into the geometry constructors adds
        # extra cost.
        try:
            if geom.geom_type in ("Point", "LineString", "LinearRing"):
                return type(geom)(zip(*func(*zip(*geom.coords))))
            elif geom.geom_type == "Polygon":
                shell = type(geom.exterior)(zip(*func(*zip(*geom.exterior.coords))))
                holes = [
                    type(ring)(zip(*func(*zip(*ring.coords))))
                    for ring in geom.interiors
                ]
                return type(geom)(shell, holes)

        # A func that assumes x, y, z are single values will likely raise a
        # TypeError, in which case we'll try again.