Fix converting to global coords in threePointArc

Add more elaborate testcases with workplane origin moved and comparing
the result of volumes created by threePointArc and sagittaArc.

cadquery/cq.py

@@ -1321,10 +1321,8 @@ def threePointArc(self, point1, point2, forConstruction=False):
         """
 
         startPoint = self._findFromPoint(False)
-        if not isinstance(point1, Vector):
-            point1 = self.plane.toWorldCoords(point1)
-        if not isinstance(point2, Vector):
-            point2 = self.plane.toWorldCoords(point2)
+        point1 = self.plane.toWorldCoords(point1)
+        point2 = self.plane.toWorldCoords(point2)
 
         arc = Edge.makeThreePointArc(startPoint, point1, point2)
 

tests/TestCadQuery.py

@@ -1619,11 +1619,22 @@ def testClose(self):
         self.assertAlmostEqual(a.val().wrapped.Volume * 2.0, b.val().wrapped.Volume)
 
         # Testcase 3 from issue #238
-        thickness = 3
-        length = 10
-        width = 5
+        thickness = 3.0
+        length = 10.0
+        width = 5.0
 
-        obj = Workplane('XY', origin=(0, 0, -thickness / 2)) \
+        obj1 = Workplane('XY', origin=(0, 0, -thickness / 2)) \
             .moveTo(length / 2, 0).threePointArc((0, width / 2), (-length / 2, 0)) \
             .threePointArc((0, -width / 2), (length / 2, 0)) \
             .close().extrude(thickness)
+
+        os_x = 8.0    # Offset in X
+        os_y = -19.5  # Offset in Y
+
+        obj2 = Workplane('YZ', origin=(os_x, os_y, -thickness / 2)) \
+            .moveTo(os_x + length / 2, os_y).sagittaArc((os_x -length / 2, os_y), width / 2) \
+            .sagittaArc((os_x + length / 2, os_y), width / 2) \
+            .close().extrude(thickness)
+
+        # The obj1 shape shall have the same volume as the obj2 shape.
+        self.assertAlmostEqual(obj1.val().wrapped.Volume, obj2.val().wrapped.Volume)