The process of creating the constraints between the source (solving) and target (retargeting) skeleton and setting the offsets is called mapping. Before mapping, ensure both skeletons are in the same pose. To do this, you enter map mode, which uses a separate clip to enable you to pose the target skeleton to match the source separately from the main clip.

First you pose the target, then you create the constraints. When you create a constraint (or click Update Offsets to update (recalculate) the offsets), its offset is calculated. (The offset is the difference in pose between the source and target.) The offset is saved to the VSR when you export it.

Later, you may need to return to map mode to tweak the setup, or just to examine how it was set up. To do this, the target must be in the same pose it was when it was mapped. The map pose makes this possible.

If constraints exist for a skeleton (implying a map pose is likely to exist), entering map mode automatically places the target skeleton into its map pose.

Use map mode

To enter map mode, which switches to the map clip and puts the skeletons in their map poses, click the Map Mode button.

In map mode, you can constrain the target skeleton to the source skeleton. To get the optimum results from the retarget, the source and target poses must be as close as possible.

Shogun Post takes any differences between the two skeletons and stores them as offsets, which are saved in the VSR file on export. Any joints with default values or keys are copied onto pre-rotation to match the source Vicon skeleton and stored as the map pose for the solver to use. The original values are maintained in the FBX or USD skeleton, enabling the skeleton to be imported back onto the original rig without any issues.

In addition to supporting the use of skeletons that use pre-rotation to define the base pose (see Retarget with Shogun Post in Getting started with Vicon Shogun), Shogun Post also supports the use of skeletons that have zeros for pre-rotation and use keys or default values to achieve this.

For example, Mannequin.FBX is a commonly used target skeleton. It contains joints like the clavicles which, instead of using pre-rotation, use keys to define a base pose, (or more accurately, the appearance of a base pose, as the actual base pose is not a real base pose.)

When Mannequin.FBX is loaded into AutoDesk® MotionBuilder®, at first glance it appears to be in a base pose:

However, notice that the pose is actually defined by a set of keys on frame 0 and the pre-rotation (as seen in the Properties) is zeros for bones like the clavicle, which have a rotation so the X axis can point to the side even though its parent has the X pointing up.

To see the actual base pose, delete the keys and set all the rotation values for all bones to zero:

This demonstrates why it's better to use the pre-rotation to define the base pose. When all keys are removed, and all bone set to zeros, it's preferable to have a base pose that's a clear T- or A-pose instead of the stack of bones shown above. It's also more sensible because the animation you place on a skeleton via mocap or hand-keying is easier to deal with when poses are relative to zero. For example, it's easier to think of a bend of the elbow as X degrees from 0, not X from 90, which is what you'd have if straight was actually 90 because of the current base pose.

Ideally, you would rebuild skeletons like this to use pre-rotation instead, but this is not always possible. When it's not possible, you can still use the skeleton, but you must set the map pose (see Retarget with Shogun Post in Getting started with Vicon Shogun).

Benefits of using map pose:

The pose used during mapping is saved and restored when you go back into map mode or load the VSR into the Retarget app.
The target skeleton matches the source skeleton's joint orientation more closely, resulting in a better solve.

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