NLA local/relative animation

Support Animation and Rigging
1

This may or may not be a nood question; I’m too much of a noob to know.

I am trying to animate simple objects using animation derived from motion tracking and then edit (trim, mix, match) the animation segments using the NLA editor, but I’m having trouble because the NLA blending between clips always moves the object back to the original coordinates before animating with the new strip. I need it to animate from its current position.

Example (simplified): The motion tracking keys makes cube1 move from 0,0 to 3,4. I make an NLA action strip out of that motion and duplicate it with the intention of having it repeat the motion from its current coordinates thereby moving from 3,4 to 6,8. But instead it slides all the way back to 0,0 and moves to 3,4 again.

After a lot of googling I think this has to do with setting global IPO and relative (local?) IPO, but I’m having no luck finding any information about how to work with these attributes, or even comprehensilbe explanations of what they are exactly.

Any help or even just pointing me in the right direction to learn how to do this would be greatly appreciated. Thank you.

2

Read this article. it explains the jump back issue your facing when using the motion capture files and how to get around it.

https://sites.google.com/site/makehumandocs/blender-export-and-mhx/mocap-tool/combining-actions-in-nla-editor

3

To do this, try the following steps:

  1. Ensure that each successive strip occurs on a track above the previous one. They should form a stairstep-like arrangement going upwards (from bottom left to top right)
  2. Ensure that each strip in this setup is set to “Extend/Hold Forwards”
  3. Now, change the “Blend Mode” on higher-up strips to “Add” instead of the default “Blend/Replace”

Now, this will only really work well if the actions used in the strips only contain F-Curves affecting the properties that you want doing this (i.e. actions should contain location F-Curves only; rotation/scale/etc. animation but should not be included in those actions unless you want them to behave in a similar manner).

4

Thank you Aligorith! My initial tests using those settings worked perfectly! You saved me a ton of workaround work. Thank you for taking the time to respond!

For anyone else trying to do this, the settings Aligorith is talking about are in the Properties side panel of the NLA editor (go to view>properties at the bottom of the NLA window; it doesn’t show up by default) and the options won’t appear unless you have an action strip selected. The two settings in the properties panel are called “Extrapolation: Hold Forward” and “Blending: Add.”

I also found out from quick testing that you have to be careful if you’re just animating the location and rotation of an object and you use “Blending: Add” after you’ve used the the auto-keyframe option (record button) or otherwise have put superfluous keyframes in the “Scale” of you’re object. Your object could grow for no apparent reason like mine did. Right-click on scale in the 3D view properties panel of your object and clear the keyframes to make it stop growing with each successive action strip.

Thanks for the link BlenderBoy; I don’t think that article answers my specific question, but there’s some other useful information in there that I will probably need.