Background 

I am working on motion capture data analysis of human walking movement. My goal is to find the variation of markers on different body part in relation to the movement of the main body.

For that I am considering upper trunk body and lower trunk body. Upper trunk body include shoulder, chest and upper abdomen. Lower body includes waist , hip ,lower back and lower abdomen. 

I have markers placed in each body location. I want to create a marker that represents just the body movement and not the surface variations and joint variations so that it can be used as a surface to create reference variation. For that purpose, I am trying to create a kinematic model

Problem

How do I create my virtual point with respect to let's say 3 markers on the upper body? Which motion analysis software can give me this functionality to create some sort of kinematic model. 

- let's say create a vector with respect to a plane made by 3 markers and then create a point from the vector with respect to the plane created by the markers.

The attached picture represents my problem for some rough visualization. Here 2 upper green markers are used to create a vector in red which is used to create a green virtual marker.