Fix geometric_objects.translate() bug for collinear axes case (#4884)

* Fix collinear direction bug

* Separate test cases for inexact direction

* Use fixture to avoid mesh each time

---------

Co-authored-by: Erik Bedard <bedarder@gmail.com>
Co-authored-by: Tetsuo Koyama <tkoyama010@gmail.com>

pyvista/core/utilities/geometric_objects.py

@@ -56,14 +56,16 @@ def translate(surf, center=(0.0, 0.0, 0.0), direction=(1.0, 0.0, 0.0)):
 
     """
     normx = np.array(direction) / np.linalg.norm(direction)
-    # assume temporary normy to calculate normz
-    norm_y_temp = [0.0, 1.0, 0.0]
-    normz = np.cross(normx, norm_y_temp)
-    if np.array_equal(normz, (0.0, 0.0, 0.0)):
-        # the assumed normy axis is parallel to normx, so shift its
-        # axis and recalculate normz
-        norm_y_temp = [-1.0, 0.0, 0.0]
-        normz = np.cross(normx, norm_y_temp)
+    normy_temp = [0.0, 1.0, 0.0]
+
+    # Adjust normy if collinear with normx since cross-product will
+    # be zero otherwise
+    if np.allclose(normx, [0, 1, 0]):
+        normy_temp = [-1.0, 0.0, 0.0]
+    elif np.allclose(normx, [0, -1, 0]):
+        normy_temp = [1.0, 0.0, 0.0]
+
+    normz = np.cross(normx, normy_temp)
     normz /= np.linalg.norm(normz)
     normy = np.cross(normz, normx)
 

tests/core/test_geometric_objects.py

@@ -4,6 +4,8 @@
 import pytest
 
 import pyvista as pv
+from pyvista import examples
+from pyvista.core.utilities.geometric_objects import translate
 
 
 def test_cylinder():
@@ -515,3 +517,30 @@ def test_icosphere():
 
     icosahedron = pv.Icosahedron()
     assert icosahedron.n_faces * 4**nsub == icosphere.n_faces
+
+
+@pytest.fixture()
+def bunny():
+    return examples.download_bunny()
+
+
+@pytest.mark.parametrize("is_negative", (True, False))
+@pytest.mark.parametrize("delta", ([0, 0, 0], [1e-8, 0, 0], [0, 0, 1e-8]))
+def test_translate_direction_collinear(is_negative, delta, bunny):
+    mesh_in = bunny
+    direction = np.array([0.0, 1.0, 0.0]) + delta
+    if is_negative:
+        direction *= -1
+    mesh_out = mesh_in.copy()
+    translate(mesh_out, direction=direction)
+    points_in = mesh_in.points
+    points_out = mesh_out.points
+
+    if is_negative:
+        assert np.allclose(points_in[:, 0], -points_out[:, 1])
+        assert np.allclose(points_in[:, 1], points_out[:, 0])
+        assert np.allclose(points_in[:, 2], points_out[:, 2])
+    else:
+        assert np.allclose(points_in[:, 0], points_out[:, 1])
+        assert np.allclose(points_in[:, 1], -points_out[:, 0])
+        assert np.allclose(points_in[:, 2], points_out[:, 2])

tests/core/test_parametric_geometry.py

@@ -153,10 +153,18 @@ def test_ParametricTorus():
 def test_direction():
     geom1 = pv.ParametricEllipsoid(300, 100, 10, direction=[1, 0, 0])
     geom2 = pv.ParametricEllipsoid(300, 100, 10, direction=[0, 1, 0])
+    geom3 = pv.ParametricEllipsoid(300, 100, 10, direction=[0, -1, 0])
     assert geom1.n_points
     assert geom2.n_points
+    assert geom3.n_points
     points1 = geom1.points
     points2 = geom2.points
+    points3 = geom3.points
+
     assert np.allclose(points1[:, 0], points2[:, 1])
     assert np.allclose(points1[:, 1], -points2[:, 0])
     assert np.allclose(points1[:, 2], points2[:, 2])
+
+    assert np.allclose(points1[:, 0], -points3[:, 1])
+    assert np.allclose(points1[:, 1], points3[:, 0])
+    assert np.allclose(points1[:, 2], points3[:, 2])