How to improve the end results

  1. The problem with Animation Retargeting
    1. Shoulders and Wrists
  2. Improve the Retarget Pose
  3. Improve the Retargeted Animation
  4. Exact hand and foot positioning

When using the UE5 Retargeting System is common to have some defects in the end results. This is caused by the different morphologies of the involved skeletal meshes, that are not taken into account by the UE5 Retargeting System. Fortunately you can easily fix this sort of issues directly inside the UE5 Editor.

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The problem with Animation Retargeting

The UE5 Retargeting System uses only the skeletons data for the computation, that means only bones rotations and relative distances. This doesn't include any information about the involved meshes (i.e. the triangles) and their rigging (i.e. which triangles are influenced by a specific bone).

For example, a mesh with bigger biceps could have its arms intersect with its chest after retargeting it with a character with smaller biceps. In fact, while the used retarget pose is ok for the smaller character, the system doesn't compute the additional rotations needed to accommodate for the bigger biceps of the other mesh.

Retargeting defects caused by different morphologies

Shoulders and Wrists

This is often the case with shoulders when retargeting a Mixamo character to the UE4 Mannequin. This is caused by the peculiar morphology of the UE4 Mannequin shoulders.

Sometimes, when using custom characters with Mixamo, a not-optimal rigging can cause issues with the shoulders and the wrists. In this case, accurately re-rigging the character with the Mixamo Auto-Rigger can improve a lot the results.

Retargeting defects caused by different morphologies

Fortunately you can easily fix this sort of issues directly inside the UE5 Editor. After having applied the plugin to the wanted Mixamo skeleton, you have two main options:

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Improve the Retarget Pose

If the involved characters have very different morphologies, manually adjusting the Retarget Pose in the used IK Retargeter asset can easily improve the result of all the retargeted animations. Usually this requires only to apply small corrections to few bone rotations. This must be done before retargeting the animations.

Below video has been recorded with UE4. A new version for UE5 will be available soon.

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Improve the Retargeted Animation

Retargeted animations can be easily fine-tuned directly inside the Unreal Engine 5: open the animation and, using the Skeleton Tree panel, tune the bones rotation as needed on the animation frames. Then save the modified Animation selecting Create Asset > Create Animation > Current Animation > Preview Mesh.

Below video has been recorded with UE4. A new version for UE5 will be available soon.

download on unreal engine marketplace

Exact hand and foot positioning

In some situations it can be important to maintain the exact same hand or foot placement as the original source animation. For example, animations for interacting with the environment (e.g. opening doors, pressing buttons, pulling levers). For these situations the IK Retargeter can be set up so that the retargeted animation will match the original hand and foot position and avoid the need to resort to expensive real-time IK solutions.

The IK Rig assets generated by the plugin include a Full Body IK setup that is used by the IK Retargeter to help improve the retargeting results. By default this is set up to use an interpolated position of the IK goal based on the skeleton of the target character, this creates more natural looking results that fit with the proportions of the character. This can be changed with a simple setting so that the IK Goal will use the source position instead resulting in the exact hand/foot placement desired.

Let’s use the arm as an example. Here we have a source animation where the Mixamo character is interacting with a door handle.

Source animation where the Mixamo character is interacting with a door handle

You can see here, when retargeted with the default setting onto the Unreal mannequin, the difference in character proportions results in the hand being out of place on the retargeted animation.

Retargeted animation with the UE4 Mannequin's hand being out of place

To fix this we’ll open up the IK Retargeter and make sure that the Retarget IK option is enabled.

The Retarget IK option

Then we’ll go to the Chain Mapping tab and select the chain for the arm we want to fix, in this case the RightArm chain. Now in the Details panel above we’ll look in the IK Adjustments section and simply change the Blend to Source option from 0 to 1.

The Blend to Source option

Now when we export the animation we can see the hand is now in the correct position.

Retargeted animation where the UE4 Mannequin is correctly interacting with the door handle

Tip: Remember to set this back to 0 before retargeting other animations that don’t require the exact hand/foot placement as it can lead to strange results.

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