setInertia(), sign definition of product moments

[Pasha van Bijlert]

Hi all,

I was wondering if someone could clear this up for me: what is the sign definition of the product moments of inertia used in OpenSim? I know I can set the inertia tensor of a body using the individual tensor elements [Ixx Iyy Izz Ixy Ixz Iyz] in a vec6, but I couldn't find what the definition is of the product moments (I've check the simbody documentation). For Ixy, is it:

negative.PNG (6.27 KiB) Viewed 148 times

or is it:

positive.PNG (5.92 KiB) Viewed 148 times

In other words, when setting the inertia tensor of a body via a vec6, do I add the minus sign myself, or does opensim/simbody do this?

Cheers,
Pasha