# moment of inertial taken at different position

what is difference between Principal axes of inertia and principal moments of inertia Taken at the center of mass,Moments of inertia Taken at the center of mass and aligned with the output coordinate system and Moments of inertia Taken at the output coordinate system ?

And why is the momet of inertia taken at center of mass and aligned with output coordinate system is used in urdf in ros?

```
Principal axes of inertia and principal moments of inertia: ( grams * square millimeters )
Taken at the center of mass.
Ix = ( 0.89, 0.45, 0.00) Px = 177217.10
Iy = (-0.45, 0.89, -0.01) Py = 632385.17
Iz = ( 0.00, 0.00, 1.00) Pz = 780108.86
Moments of inertia: ( grams * square millimeters )
Taken at the center of mass and aligned with the output coordinate system.
Lxx = 268506.70 Lxy = 182259.67 Lxz = -4.63
Lyx = 182259.67 Lyy = 541099.71 Lyz = -851.31
Lzx = -4.63 Lzy = -851.31 Lzz = 780104.72
Moments of inertia: ( grams * square millimeters )
Taken at the output coordinate system.
Ixx = 364622.20 Ixy = -112574.17 Ixz = -2115.49
Iyx = -112574.17 Iyy = 1445552.39 Iyz = -163.21
Izx = -2115.49 Izy = -163.21 Izz = 1780663.05
```