Blender: Walk around sphere

Question

In order to understand blender python game scripting, I currently try to build a scene in which one can walk around a sphere, using the FPSController structure from this link. For gravity and FPSController orientation I tried to construct a python Controller, which currently looks like this:

def main():     print("Started")      controller = bge.logic.getCurrentController()     me = controller.owner      distance, loc, glob = me.getVectTo((0,0,0))      grav = controller.actuators['Gravity']      strength = me['Gravity']     force = strength*(distance*distance)*glob      grav.force = force      try:         rot = Vector((0,0,-1)).rotation_difference(glob).to_matrix()     except Exception as E:         print(E)         rot = (0,0,0)      rotZ = me.orientation     me.orientation = rot*rotZ      controller.activate(grav)  main() 

which roughly works until any angle goes over 180 degrees, and looks discontinuous then. I assume this comes from rotation_difference being discontinuous – blender documentation on Math Types & Utilities does not say anything, and I have not thought enough about quaternionic representations yet to see if a continuous map would be possible – and I guess there is a more elegant way to achieve that the local Z orientation is continuously mouse-dependent, while local X and Y orientations depend continuously on some given vector, but how?

Answer 1

The consensus seems to be that you should accomplish such rotations using quaternions.

See this for the api: http://www.blender.org/documentation/249PythonDoc/Mathutils.Quaternion-class.html

See this for an introduction to the maths: http://en.wikipedia.org/wiki/Rotation_formalisms_in_three_dimensions#Quaternions