test_shapely.py

"""A series of tests to see how shapely works."""

import numpy as np
import shapely.geometry
import watershed_workflow.utils


def test_intersection_intersects():
    """Does the intersection of two shapes always intersect those shapes?  SURPRISE"""
    shp = shapely.geometry.Polygon([(1.03425, 0.0013), (0.0035, 1.03523), (-1.09824, 0.0033),
                                    (0.0012, -1.04856)])
    line = shapely.geometry.LineString([(0.1394, 0.0492), (3.1415, 1.1394)])

    # check if a linestring intersecting a linestring intersects the line
    p = shp.boundary.intersection(line)

    # Lesson learned:
    # The intersection of two lines does not always intersect either line!
    # Nonrobustness of point geometry!
    assert (not shp.boundary.intersects(p))
    assert (not line.intersects(p))

    # same as
    assert (not shp.boundary.contains(p))

    # is this obviously safe?  NO!
    assert (shp.contains(p))


def test_simplify():
    """Does simplify ever move the end points of a linestring?  YAY!"""
    coords = np.array([(-.001, -.001), (0, 0), (100, 0), (100.001, .001)])

    def wiggle(coords):
        random = np.random.random((len(coords), 2))
        random = 2 * (random-.5) * .001
        return coords + random

    good = []
    for i in range(100):
        newc = wiggle(coords)
        ls = shapely.geometry.LineString(newc)
        ls_s = ls.simplify(.01)
        mygood = ((len(ls_s.coords) == 2)
                  and watershed_workflow.utils.close(ls_s.coords[0], ls.coords[0], 1.e-10)
                  and watershed_workflow.utils.close(ls_s.coords[-1], ls.coords[-1], 1.e-10))
        good.append(mygood)

    print("Good % = ", sum(1 for i in good if i) / 100.0)
    assert (all(good))


def test_snap():
    """How does snap work?  IT DOESN'T merge points"""
    coords = np.array([(-.001, -.001), (100, 0), (100.001, .001)])
    l = shapely.geometry.LineString(coords)

    c2 = np.array([(100, -100), (0, 0), (-100, 100)])
    l2 = shapely.geometry.LineString(c2)

    ls = shapely.ops.snap(l, l2, 1)
    print(list(ls.coords))
    assert (len(ls.coords) is 3)
    assert (watershed_workflow.utils.close(l2.coords[1], ls.coords[0], 1.e-8))


def test_snap2():
    """How does snap work? will it snap to a midpoint of the segment?  NO"""
    coords = np.array([(-.001, -.001), (100, 0)])
    l = shapely.geometry.LineString(coords)

    c2 = np.array([(100, -100), (-100, 100)])
    l2 = shapely.geometry.LineString(c2)

    ls = shapely.ops.snap(l, l2, 1)
    print(list(ls.coords))
    assert (len(ls.coords) is 2)
    assert (watershed_workflow.utils.close(ls.coords[0], l.coords[0], 1.e-8))


def test_kdtree():
    """Does kdtree replicate duplicated points?  YES"""
    import scipy.spatial
    coords = np.array([(0., 0.), (0., 0.)])
    kdtree = scipy.spatial.cKDTree(coords)
    closest = kdtree.query_ball_point(np.array([0.0000001, 0.0000001]), 1.e-5)
    assert (len(closest) is 2)