fix randomness in orientation function

Author: tomvanmele

CHANGELOG.md

@@ -18,7 +18,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Fixed `native_edge` property of `RhinoBrepEdge`.
 * Expose the parameters `radius` and `nmax` from `compas.topology._face_adjacency` to `compas.topology.face_adjacency` and further propagate them to `unify_cycles` and `Mesh.unify_cycles`.
-* Modify `face_adjacency` to avoid using `compas.topology._face_adjacency` by default when there are more than 100 faces, unless one of the parameters `radius`, `nmax` is passed
+* Modify `face_adjacency` to avoid using `compas.topology._face_adjacency` by default when there are more than 100 faces, unless one of the parameters `radius`, `nmax` is passed.
+* Changed `unify_cycles` to use the first face in the list as root if no root is provided.
 
 ### Removed
 

src/compas/topology/orientation.py

@@ -193,6 +193,11 @@ def unify_cycles(vertices, faces, root=None, nmax=None, max_distance=None):
     Exception
         If no all faces are included in the unnification process.
 
+    Notes
+    -----
+    The cycles of the faces will be aligned with the cycle direction of the root face.
+    If no root face is specified, the first face in the list will be used.
+
     """
 
     def unify(node, nbr):
@@ -210,7 +215,8 @@ def unify(node, nbr):
                     return
 
     if root is None:
-        root = random.choice(list(range(len(faces))))
+        # root = random.choice(list(range(len(faces))))
+        root = 0
 
     adj = face_adjacency(vertices, faces, nmax=nmax, max_distance=max_distance)  # this is the only place where the vertex coordinates are used
 

tests/compas/topology/test_unify_cycles.py

@@ -14,6 +14,7 @@
 def test_unify_cycles():
     if compas.IPY:
         return
+
     test_data = compas.json_load(os.path.join(HERE, "..", "fixtures", "topology", "vertices_faces.json"))
     vertices = test_data["vertices"]
     faces = test_data["faces"]
@@ -25,12 +26,15 @@ def test_unify_cycles():
     # no parameters
     unify_cycles(vertices, faces)
     assert TOL.is_close(volume, volume_polyhedron((vertices, faces)))
+
     # only max_nbrs
     unify_cycles(vertices, faces, nmax=max_nbrs)
     assert TOL.is_close(volume, volume_polyhedron((vertices, faces)))
+
     # only max_distance
     unify_cycles(vertices, faces, max_distance=max_edge_length)
     assert TOL.is_close(volume, volume_polyhedron((vertices, faces)))
+
     # both parameters
     unify_cycles(vertices, faces, nmax=max_nbrs, max_distance=max_edge_length)
     assert TOL.is_close(volume, volume_polyhedron((vertices, faces)))