Preferred retargeting workflow for meshes with different proportions using the same skeleton

Development Character & Animation
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Hi,

I have some questions regarding animation retargeting. In our project, we want to reuse animations created for a male skeletal mesh (based on the UE5_Mannequin) on a female skeletal mesh that has different proportions. Currently, animations like reload sequences result in incorrect hand contact positions when played on the female character.

From what I understand, we have two main options:

Translation Retargeting

This might help align overall motion, but it likely won’t fix the incorrect hand contact. I was considering using the IK bones (which are children of the root) as IK effectors to correct hand placement, since IK bones shouldn’t be affected by the retargeting process. However, I assume this could cause arm stretching if the proportions differ significantly, and it probably wouldn’t solve hand or finger clipping issues.

If I go with this approach:

  • What translation retargeting settings would you recommend applying to the skeleton?
  • Should I be concerned about virtual bones being affected by the retargeting process?

IK Retargeter

Although both meshes share the same skeleton, I’m wondering if the IK Retargeter could still be useful in this case to compensate for proportion differences. I noticed that Unreal 5.6 added a new “Scaled Proportional Retargeting” option to the IK Retargeter, which might help reduce arm stretching.

If I choose this approach:

  • Do I still need to use translation retargeting as well, or should I disable it?
  • If it should be disabled, what’s the proper way to do that?

Given this setup, which approach (or combination of approaches) would you recommend to best preserve animation quality and maintain correct hand contact when reusing these animations across meshes with different proportions or are there maybe other options I haven’t considered?

Kind regards,

Van Brabant Maxim

2

Hey there,

You have a good handle of the current tools that we offer and their use case.

What translation retargeting settings would you recommend applying to the skeleton?

This really depends on the differences between your skeleton, but for the most part, Animation Scaled will be the primary setting for most bones, except for your pelvis and root bones. I have also found that you’ll want to pay special attention to the finger joint positions; you might need to change the settings for those to Animation Relative, as the translational offset that can happen with animation scaled breaks the hands.

Should I be concerned about virtual bones being affected by the retargeting process?

Virtual bones don’t have any animation on them to gather data from, but they could be modified positionally from their parent bone, which would be the primary concern. In the case of your IK bones, you want to include them in your skeleton and set them to Animation to get the absolutely correct world position for your character.

Long ago, Laurent did an overview of runtime retargeting in a live training session, and there is still a lot of relevant information in that video. Keep in mind this is in Unreal 4, so things might have moved or changed a bit.

https://www.youtube.com/watch?v=vZW8mxlQJEk

Do I still need to use translation retargeting as well, or should I disable it?

It is a two pass process, first the translation retarget will happen and then the IK will happen. You can decide based your skeleton’s differences, but as an example we use all of the workflows you’re describing in the Gameplay Animation Sample Project and each of the meshes has their own setting to have animations work the best.

If it should be disabled, what’s the proper way to do that?

If you want to “disable” the translation retargeting, you would set each of the bones to be Skeleton, which basically says only use the translational offsets from the skeleton’s ref pose.

Given this setup, which approach (or combination of approaches) would you recommend to best preserve animation quality and maintain correct hand contact when reusing these animations across meshes with different proportions or are there maybe other options I haven’t considered?

The recommendation is to start with translational retargeting, if you can hit the mark you are trying to hit with that, you will gain the most performance benefit. But this setup that you can follow here is an excellent overview of the next step you can take for many of your characters and one we use in Fortnite a lot for characters with large enough deltas in their proportions.

https://dev.epicgames.com/documentation/en-us/unreal-engine/runtime-ik-retargeting-in-unreal-engine

For most cases, you can use an IK retarget asset with these operations:

  • Pelvis
  • FK Chain
  • IK Goal

And that will do majority of the rest of the work. Greg goes over the new UI and some of the new operations here, but those operations are often targeting large character differences where you need to do something very specific.

https://www.youtube.com/watch?v=-8CQNaODNNA

Hope this helps,

Dustin