Optimum Common Shape Technique (OCST) is a mathematical approach that finds the Average or Common shape for selected sets of markers (3 or more). The first pass through all frames allows the process to see each shape configuration. From this a common shape is calculated. The second pass through the data for processing forces the common shape and creates virtual markers. Alternatively, the real trajectories can be left in place (not moved or replaced) but the Segment elements can be calculated using the new positions.

OCST is important as it allows a non-rigid cluster (skin based markers) to be described as if it were truly rigid. Forcing a virtual rigidity allows the use of other algorithms that are reliant on an expectation of rigidity (i.e SCoRE and SARA).

The OCST method has been implemented in Nexus 2.

Research Publication: W.R. Taylor, E.I. Kornaropoulos, G.N. Duda, S. Kratzenstein, R.M. Ehrig, A. Arampatzis, M.O. Heller. Repeatability and reproducibility of OSSCA, a functional approach for assessing the kinematics of the lower limb. Gait & Posture 32 (2010) 231–236