New IfcOpenShell placement utility module

src/ifcopenshell-python/ifcopenshell/util/placement.py

@@ -0,0 +1,25 @@
+import numpy as np
+
+def a2p(o, z, x):
+    y = np.cross(z, x)
+    r = np.eye(4)
+    r[:-1, :-1] = x, y, z
+    r[-1, :-1] = o
+    return r.T
+
+
+def get_axis2placement(plc):
+    z = np.array(plc.Axis.DirectionRatios if plc.Axis else (0, 0, 1))
+    x = np.array(plc.RefDirection.DirectionRatios if plc.RefDirection else (1, 0, 0))
+    o = plc.Location.Coordinates
+    return a2p(o, z, x)
+
+
+def get_local_placement(plc):
+    if plc is None:
+        return np.eye(4)
+    if plc.PlacementRelTo is None:
+        parent = np.eye(4)
+    else:
+        parent = get_local_placement(plc.PlacementRelTo)
+    return np.dot(get_axis2placement(plc.RelativePlacement), parent)