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Custom Shadow Segments
Virtual segments provide a convenient way to include multiple definitions for a segment within a single model, but these multiple definitions do not easily allow for external constraints (like an Inverse Kinematic chain) to be applied consistently across all segment definitions. For example, if a Virtual Segment is defined with relation to a segment and then an Inverse Kinematics constraint is applied to the original segment, the changes in the original segment's pose estimation do not propagate to the Virtual Segment.
Shadow segments resolve this issue by allowing that segment's pose to be defined as a transformation of the original segment's pose estimation. Users can use the Expression function Pose_4x4 when defining their own shadow segments.