arena expression , how to get head rotation?

[NaturalPoint - Mike]

Head rotations in Motionbuilder will come through, however in order to get them to come through you have to select "expression" in the optical device properties. This lets motionbuilder know that head rotation should be tied to the expression data.

[lalamax3d]

thanks mike.
can u please also shed some light, how arena, estimate head rotations and translation data. is it possible to get that data directly from four head markers. then it will be easy for us, to directly use c3d in blender.
if your developer can share some basic points (steps) that will help. in last week, i have tested lot of variations (rig tests)by averaging trasnlation from head markers and then measure offset to head bone. then getting rotations copied from bone to nose marker. etc..
any ideas? thanks..

[NaturalPoint - Mike]

The center of the head bone is defined as one quarter the distance between the chin marker and the eyebrow marker above the chin, and one half the distance between the chin marker and eyebrow marker back.