Results from IK - Generalized coordinates misunderstanding

[Michala Cadova]

Hi,
I have maybe a silly question, but the results from the Inverse kinematics (IK) such as translations and rotations are related to the coordinate system, right? Not to the joint. I am asking because I somehow cannot connect the results when I plot them and the animation when I “animate” the results. I mean, in the model when I load the motion (results from the IK) it seems that the origin of the coordinate system goes backward (in the negative sense on axis X) and then back to the front (nearly in one plane). But when I plot the results from IK, then the generalized coordinate corresponding to this movement goes to the positive values. How, why? Moreover, just to test – if I manually change the sign of this generalized coordinate, visually (when I load the motion to the model) nothing change! The movement seems exactly the same – but I would expect opposite movement in the X-axis. What is wrong? Do I understand it wrong?

Michala

[Ayman Habib]

Hi Michala,

The results from IK are in "generalized coordinates" (also known as internal coordinates) these are the coordinates that parametrize joints and you can see a list of them in the coordinates window in the GUI. The units for rotational coordinates are internally in radians (depending on the motion/sto file header) but they get converted to degrees for display purposes by the GUI. Since the motion has coordinate values, when you associate it with a model, it overrides the current value so the behavior you describe is expected.

Hope this helps,
-Ayman