def get_ring_coords(polygon):
# outer ring must be reversed to be counterclockwise[::-1]
coords = [pg.get_coordinates(pg.get_exterior_ring(polygon)).tolist()]
for i in range(pg.get_num_interior_rings(polygon)):
# inner rings must be reversed to be clockwise[::-1]
coords.append(
pg.get_coordinates(pg.get_interior_ring(polygon, i)).tolist())
return coords
def test_get_rings_return_index():
geom = np.array([polygon, None, empty_polygon, polygon_with_hole])
expected_parts = []
expected_index = []
for i, g in enumerate(geom):
if g is None or pygeos.is_empty(g):
continue
expected_parts.append(pygeos.get_exterior_ring(g))
expected_index.append(i)
for j in range(0, pygeos.get_num_interior_rings(g)):
expected_parts.append(pygeos.get_interior_ring(g, j))
expected_index.append(i)
parts, index = pygeos.get_rings(geom, return_index=True)
assert len(parts) == len(expected_parts)
assert np.all(pygeos.equals_exact(parts, expected_parts))
assert np.array_equal(index, expected_index)
def second_areal_moment(collection):
"""
Using equation listed on en.wikipedia.org/Second_Moment_of_area, the second
moment of area is actually the cross-moment of area between the X and Y
dimensions:
I_xy = (1/24)\sum^{i=N}^{i=1} (x_iy_{i+1} + 2*x_iy_i + 2*x_{i+1}y_{i+1} +
x_{i+1}y_i)(x_iy_i - x_{i+1}y_i)
where x_i, y_i is the current point and x_{i+1}, y_{i+1} is the next point,
and where x_{n+1} = x_1, y_{n+1} = 1.
This relation is known as the:
- second moment of area
- moment of inertia of plane area
- area moment of inertia
- second area moment
and is *not* the mass moment of inertia, a property of the distribution of
mass around a shape.
"""
ga = _cast(collection)
result = numpy.zeros(len(ga))
n_holes_per_geom = pygeos.get_num_interior_rings(ga)
for i, geometry in enumerate(ga):
n_holes = n_holes_per_geom[i]
for hole_ix in range(n_holes):
hole = pygeos.get_coordinates(pygeos.get_interior_ring(
ga, hole_ix))
result[i] -= _second_moa_ring(hole)
n_parts = pygeos.get_num_geometries(geometry)
for part in pygeos.get_parts(geometry):
result[i] += _second_moa_ring(pygeos.get_coordinates(part))
# must divide everything by 24 and flip if polygon is clockwise.
signflip = numpy.array([-1, 1])[pygeos.is_ccw(ga).astype(int)]
return result * (1 / 24) * signflip
def get_interior_rings(polygons):
"""Return array of inner rings for all polygons.
Parameters
----------
polygons : ndarray
All items must be Polygon geometry type
Returns
-------
(outer_index, inner_index, rings)
"""
num_rings = pg.get_num_interior_rings(polygons)
outer_index = []
inner_index = []
rings = []
for i in range(len(polygons)):
if num_rings[i]:
ix = np.arange(num_rings[i])
rings.extend(pg.get_interior_ring(polygons[i], ix))
inner_index.extend(ix)
outer_index.extend([i] * num_rings[i])
return outer_index, inner_index, rings
def test_get_interior_ring_non_polygon(geom):
actual = pygeos.get_interior_ring(geom, [0, 2, -1])
assert pygeos.is_missing(actual).all()
def test_get_interior_ring():
actual = pygeos.get_interior_ring(polygon_with_hole, [0, -1, 1, -2])
assert pygeos.equals(actual[0], actual[1]).all()
assert pygeos.is_missing(actual[2:4]).all()
def test_get_rings_holes():
rings = pygeos.get_rings(polygon_with_hole)
assert len(rings) == 2
assert rings[0] == pygeos.get_exterior_ring(polygon_with_hole)
assert rings[1] == pygeos.get_interior_ring(polygon_with_hole, 0)
