COP transformation with PointKinematics

Dimitrios Tsaopoulos · Post by **Dimitrios Tsaopoulos** » Mon Feb 22, 2010 5:49 pm

Hi,

I am trying to transform the COPs location from the toes body coordinate system to the Global ccordinate system.The XYZ axes of each body (at neutral positions) are alligned with the global coordinate system.I have used the pointkinematic analysis to find the position of the toes body origin in the global system during each step of walking and then i add these offsets to my COP data.
Then i tried to validate the calculations by
attaching a marker in the OpenSim GUI to a position that corresponds in some of the COPs relative to the toes body and then change the body to ground
For example: i add a marker with respect to the toes body with coordinates
X: 0.15893 Y:-0.0046 Z: 0.025823 (which is the one of COP location during the stance phase)

then i change the body to ground and the marker location that gives me with respect to the ground is different than the one that i have calculated by using point kinematic analysis.

COP with respect to gobal at t=0.449751

X: 1.779028307 Y: -0.084070493 Z:0.948114394 (using pointKinematic analysis)

X: 1.68630 Y: -0.07702 Z: 0.88984 (by adding a marker! These data look more realistic)

any suggestions please??

Many thanks,
Dimitris