Correct calculation in ProjectPointToPlane (#702)

Use unit normal for projection.

Update InterpolatePointTest to capture projection edges cases
- Resize the sample grid and add a gradient to the field
  to check projection normalisation.

Signed-off-by: Rhys Mainwaring <[email protected]>
Co-authored-by: Addisu Z. Taddese <[email protected]>
(cherry picked from commit 06d73ac)

Author: 2 people

include/gz/math/detail/InterpolationPoint.hh

@@ -211,8 +211,9 @@ namespace gz::math
       (_points[_start_index + 1].position - _points[_start_index].position)
       .Cross(
       _points[_start_index + 2].position - _points[_start_index].position);
+    auto n_unit = n.Normalized();
     return
-      _pos - n.Dot(_pos - _points[_start_index].position) * n.Normalized();
+      _pos - n_unit.Dot(_pos - _points[_start_index].position) * n_unit;
   }
 
   /// \brief Trilinear interpolation of eight points in 3D space. It assumes

src/InterpolationPoint_TEST.cc

@@ -86,26 +86,26 @@ TEST(Interpolation, TrilinearInterpolate)
 {
   std::vector<InterpolationPoint3D<double>> vec {
     InterpolationPoint3D<double>{Vector3d{0, 0, 0}, 0},
-    InterpolationPoint3D<double>{Vector3d{1, 0, 0}, 1},
-    InterpolationPoint3D<double>{Vector3d{0, 1, 0}, 2},
-    InterpolationPoint3D<double>{Vector3d{1, 1, 0}, 3},
-    InterpolationPoint3D<double>{Vector3d{0, 0, 1}, 4},
-    InterpolationPoint3D<double>{Vector3d{1, 0, 1}, 5},
-    InterpolationPoint3D<double>{Vector3d{0, 1, 1}, 6},
-    InterpolationPoint3D<double>{Vector3d{1, 1, 1}, 7},
+    InterpolationPoint3D<double>{Vector3d{2, 0, 0}, 1},
+    InterpolationPoint3D<double>{Vector3d{0, 2, 0}, 2},
+    InterpolationPoint3D<double>{Vector3d{2, 2, 0}, 3},
+    InterpolationPoint3D<double>{Vector3d{0, 0, 2}, 4},
+    InterpolationPoint3D<double>{Vector3d{2, 0, 2}, 5},
+    InterpolationPoint3D<double>{Vector3d{0, 2, 2}, 6},
+    InterpolationPoint3D<double>{Vector3d{2, 2, 2}, 7},
   };
 
-  std::vector<double> values {0, 0, 0, 0, 1, 1, 1, 1};
+  std::vector<double> values {0, 0, 0, 0, 1, 1, 2, 2};
 
-  auto v0 = TrilinearInterpolate(vec, values, Vector3d{0.5, 0.5, 0.5});
-  EXPECT_NEAR(v0, 0.5, 1e-3);
+  auto v0 = TrilinearInterpolate(vec, values, Vector3d{1, 1, 1});
+  EXPECT_NEAR(v0, 0.75, 1e-3);
 
-  auto v1 = TrilinearInterpolate(vec, values, Vector3d{0.5, 0.5, 0});
+  auto v1 = TrilinearInterpolate(vec, values, Vector3d{1, 1, 0});
   EXPECT_NEAR(v1, 0, 1e-3);
 
-  auto v2 = TrilinearInterpolate(vec, values, Vector3d{0.5, 0.5, 1});
-  EXPECT_NEAR(v2, 1, 1e-3);
+  auto v2 = TrilinearInterpolate(vec, values, Vector3d{1, 1, 2});
+  EXPECT_NEAR(v2, 1.5, 1e-3);
 
-  auto v3 = TrilinearInterpolate(vec, values, Vector3d{1, 1, 1});
-  EXPECT_NEAR(v3, 1, 1e-3);
+  auto v3 = TrilinearInterpolate(vec, values, Vector3d{2, 2, 2});
+  EXPECT_NEAR(v3, 2, 1e-3);
 }