1. Add CenterOfBoundBox() and CombinedCenterOfBoundBox() functions into Shape class; 2. Add another parameter centerOption into CQ.workplane([offset, invert]), and default the parameter to CenterOfMass which is the current behavior.

cadquery/CQ.py

@@ -262,7 +262,7 @@ class CQ(object):
 
         return self.objects[0].wrapped
 
-    def workplane(self, offset=0.0, invert=False):
+    def workplane(self, offset=0.0, invert=False, centerOption='CenterOfMass'):
         """
         Creates a new 2-D workplane, located relative to the first face on the stack.
 
@@ -341,7 +341,11 @@ class CQ(object):
             if not all(_isCoPlanar(self.objects[0], f) for f in self.objects[1:]):
                 raise ValueError("Selected faces must be co-planar.")
 
-            center = Shape.CombinedCenter(self.objects)
+	    if centerOption == 'CenterOfMass':            
+		center = Shape.CombinedCenter(self.objects)
+	    elif centerOption == 'CenterOfBoundBox':
+		center = Shape.CombinedCenterOfBoundBox(self.objects)
+
             normal = self.objects[0].normalAt()
             xDir = _computeXdir(normal)
 
@@ -349,12 +353,18 @@ class CQ(object):
             obj = self.objects[0]
 
             if isinstance(obj, Face):
-                center = obj.Center()
+		if centerOption == 'CenterOfMass':
+                    center = obj.Center()
+		elif centerOption == 'CenterOfBoundBox':
+                    center = obj.CenterOfBoundBox()
                 normal = obj.normalAt(center)
                 xDir = _computeXdir(normal)
             else:
                 if hasattr(obj, 'Center'):
-                    center = obj.Center()
+		    if centerOption == 'CenterOfMass':
+		        center = obj.Center()
+		    elif centerOption == 'CenterOfBoundBox':
+		        center = obj.CenterOfBoundBox()
                     normal = self.plane.zDir
                     xDir = self.plane.xDir
                 else:

cadquery/freecad_impl/shapes.py

@@ -199,6 +199,20 @@ class Shape(object):
         else:
             raise ValueError("Cannot find the center of %s object type" % str(type(self.Solids()[0].wrapped)))
 
+    def CenterOfBoundBox(self):
+        if isinstance(self.wrapped, FreeCADPart.Shape):
+            # If there are no Solids, we're probably dealing with a Face or something similar
+            if len(self.Solids()) == 0:
+                return Vector(self.wrapped.BoundBox.Center)
+            elif len(self.Solids()) == 1:
+                return Vector(self.Solids()[0].wrapped.BoundBox.Center)
+            elif len(self.Solids()) > 1:
+                return self.CombinedCenterOfBoundBox(self.Solids())
+        elif isinstance(self.wrapped, FreeCADPart.Solid):
+            return Vector(self.wrapped.BoundBox.Center)
+        else:
+            raise ValueError("Cannot find the center(BoundBox's) of %s object type" % str(type(self.Solids()[0].wrapped)))
+
     @staticmethod
     def CombinedCenter(objects):
         """
@@ -215,6 +229,22 @@ class Shape(object):
 
         return Vector(sum_wc.multiply(1./total_mass))
 
+    @staticmethod
+    def CombinedCenterOfBoundBox(objects):
+        """
+        Calculates the center of BoundBox of multiple objects.
+
+        :param objects: a list of objects with mass 1
+        """
+        total_mass = len(objects)
+        weighted_centers = [o.wrapped.BoundBox.Center.multiply(1.0) for o in objects]
+
+        sum_wc = weighted_centers[0]
+        for wc in weighted_centers[1:] :
+            sum_wc = sum_wc.add(wc)
+
+        return Vector(sum_wc.multiply(1./total_mass))
+
     def Closed(self):
         return self.wrapped.Closed