This operation calculates the skeleton's marker positions from a ROM trial. This operation is useful if the skeleton has already been scaled appropriately for the subject and more accurate marker position information is required. Any parameters that are shared between bones and markers are not altered. The operation finishes by calculating joint and marker statistics (see Calculate Skeleton Joint & Marker Statistics operation).
The Functional Skeleton Calibration - Markers Only operation is very similar to the full Functional Skeleton Calibration algorithm (see Functional Skeleton Calibration operation). The only difference is that the parameters that refer to segments positions are kept constant. For this algorithm to provide good labeling results, the skeleton must already be the correct size. You can achieve this in the following ways:
❙ Scale the template skeleton to a reconstruction point cloud.
❙ Recalibrate a subject after adjusting its markers.
Compared with the full Functional Skeleton Calibration operation, the Markers Only version has an extra step at the beginning. In this step, the parameters that influence segment properties (bone lengths) are identified. These parameters are held constant during the operation. If a parameter refers to both a segment and a marker, it is also held constant. This reduction in parameters to estimate means that a Markers Only calibration tends to be faster than a full calibration.
The algorithm uses the same criteria as the full skeleton calibration to decide how to move the marker parameters and joint angles for each selected frame. It also runs the algorithm to calculate the joint and marker statistics.
Recalibration of an existing skeleton when the markers have moved, for example, when an orthosis has been applied. If the orthosis is expected to move significantly with respect to the underlying segment, this operation is more suitable than Static Skeleton Calibration - Markers Only because this operation updates the marker covariances as well as the marker positions.
For information on how to use this operation in common Nexus workflows, see Subject calibration workflows.