Merge pull request #814 from compas-dev/area

fixes #812

CHANGELOG.md

@@ -21,6 +21,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Changed base object of `compas.datastructures.Datastructure` to `compas.data.Data`.
 * Changed base object of `compas.geometry.Primitive` to `compas.data.Data`.
 * Renamed `Base` to `Data` for all data based classes.
+* Fixed calculation of triangle normals.
+* Fixed calculation of triangle areas.
 
 ### Removed
 

src/compas/geometry/_core/normals.py

@@ -7,7 +7,6 @@
 from compas.geometry._core import cross_vectors
 from compas.geometry._core import cross_vectors_xy
 from compas.geometry._core import length_vector
-from compas.geometry._core import length_vector_xy
 from compas.geometry._core import normalize_vector
 
 from compas.geometry._core import centroid_points
@@ -67,7 +66,7 @@ def normal_polygon(polygon, unitized=True):
         nz += n[2]
 
     if not unitized:
-        return [0.5 * nx, 0.5 * ny, 0.5 * nz]
+        return [nx, ny, nz]
 
     return normalize_vector([nx, ny, nz])
 
@@ -97,7 +96,7 @@ def normal_triangle(triangle, unitized=True):
     ac = subtract_vectors(c, a)
     n = cross_vectors(ab, ac)
     if not unitized:
-        return [0.5 * n[0], 0.5 * n[1], 0.5 * n[2]]
+        return n
     lvec = 1 / length_vector(n)
     return [lvec * n[0], lvec * n[1], lvec * n[2]]
 
@@ -127,6 +126,5 @@ def normal_triangle_xy(triangle, unitized=True):
     ac = subtract_vectors_xy(c, a)
     n = cross_vectors_xy(ab, ac)
     if not unitized:
-        return [0.5 * n[0], 0.5 * n[1], 0]
-    lvec = 1 / length_vector_xy(n)
-    return [lvec * n[0], lvec * n[1], 0]
+        return n
+    return [0, 0, n[2] / length_vector(n)]

src/compas/geometry/_core/size.py

@@ -9,7 +9,6 @@
 from compas.geometry._core import subtract_vectors
 from compas.geometry._core import subtract_vectors_xy
 from compas.geometry._core import length_vector
-from compas.geometry._core import length_vector_xy
 from compas.geometry._core import cross_vectors
 from compas.geometry._core import cross_vectors_xy
 from compas.geometry._core import dot_vectors
@@ -128,7 +127,7 @@ def area_triangle_xy(triangle):
         The area of the triangle.
 
     """
-    return 0.5 * length_vector_xy(normal_triangle_xy(triangle, False))
+    return 0.5 * length_vector(normal_triangle_xy(triangle, False))
 
 
 def volume_polyhedron(polyhedron):

tests/compas/geometry/test_basics.py → tests/compas/geometry/test_core.py

@@ -1,8 +1,10 @@
-from math import pi
+from math import pi, radians, sqrt
 
 import pytest
 
 from compas.geometry import Polyhedron
+from compas.geometry import Polygon
+from compas.geometry import Rotation
 from compas.geometry import allclose
 from compas.geometry import angle_vectors
 from compas.geometry import angle_planes
@@ -13,6 +15,26 @@
 from compas.geometry import length_vector
 from compas.geometry import subtract_vectors
 from compas.geometry import volume_polyhedron
+from compas.geometry import area_polygon
+from compas.geometry import area_polygon_xy
+from compas.geometry import area_triangle
+from compas.geometry import area_triangle_xy
+
+
+@pytest.fixture
+def R():
+    return Rotation.from_axis_and_angle([0, 1, 0], radians(-90))
+
+
+@pytest.fixture
+def square():
+    return Polygon.from_sides_and_radius_xy(4, sqrt(0.5 ** 2 + 0.5 ** 2))
+
+
+@pytest.fixture
+def triangle():
+    return Polygon([[0, 0, 0], [1, 0, 0], [0, 1, 0]])
+
 
 # ==============================================================================
 # angles
@@ -156,3 +178,27 @@ def test_volume_polyhedron(polyhedron, volume):
         volume = L * L * L
     V = volume_polyhedron(polyhedron)
     assert close(V, volume)
+
+
+def test_area_square(square, R):
+    assert close(area_polygon(square.points), 1)
+    assert close(area_polygon_xy(square.points), 1)
+    assert close(square.area, 1)
+    square.transform(R)
+    assert close(area_polygon(square.points), 1)
+    assert close(area_polygon_xy(square.points), 0)
+    assert close(square.area, 1)
+
+
+def test_area_triangle(triangle, R):
+    assert close(area_polygon(triangle.points), 0.5)
+    assert close(area_polygon_xy(triangle.points), 0.5)
+    assert close(area_triangle(triangle.points), 0.5)
+    assert close(area_triangle_xy(triangle.points), 0.5)
+    assert close(triangle.area, 0.5)
+    triangle.transform(R)
+    assert close(area_polygon(triangle.points), 0.5)
+    assert close(area_polygon_xy(triangle.points), 0.0)
+    assert close(area_triangle(triangle.points), 0.5)
+    assert close(area_triangle_xy(triangle.points), 0.0)
+    assert close(triangle.area, 0.5)