MB_actor

MotionBuilder: Actor -- modified from and added to Brian Windsor (OSU/ACCAD)'s notes. Many thanks to Brian!!
Last updated 9/22/2009

Instead of directly importing motion data that exported out of iQ into Maya, we bring the data into MotionBuilder and apply the data to the skeleton of a 3D character that is imported from Maya. Then, we bring back the skeleton with the motion data to Maya.

We go though MotionBuilder because MotionBuilder is a good tool for "retargeting," where retargeting means adapting motion to a character often with a proportion that is different from the proportion of the capture subject. For more information about retargeting read Michael Gleicher's paper.

MotionBuilder has an intermediate "skeleton" called an Actor. It's a set of constraints that will be the source motion for your character. First we have to match the marker points to corresponding areas of the actor (Steps 1 - 3 below).

Step 1. Importing marker data
Step 2. Bringing in Actor
Step 3. Matching Actor to markers
Step 4. Creating a marker set
Step 5. Exporting the marker set
Step 6. Activate the character
Step 7. Re-using the marker set
Step 8. Character

1. Importing marker data. The first thing to do is bring in a .C3D file. Go to File -> Import… and select Vicon (*.c3d) as the file type. If this is the first time for you to go though this process, you should find a T-pose. The icons for navigations stand for rotating the camera, moving the camera, dolly in/out, zoom in/out, and tilting cameras respectively

2. Bringing in Actor. Next we'll need to drag an actor into our space. The Actor icon is located in the Templates section of the Asset Browser (See the screen capture below. You find a tab for Asset Browser together with Pose Controls, Properties, and Filters in the pane in the lower right corner). Within Templates directory is the Characters section and within that are both Actor and Character. For this part, you only want Actor. Notice that there are also facial actor and character set ups.

3. Matching Actor to markers. Scale, translate, and rotate Actor and Actor's segments until they match up. Start from the hip segment and work towards the ends of extremities. The translate, rotate, and scale tools (the screen capture below) are on the right side of Viewer. The mask for objects (the screen capture below) helps you selecting Actor's segments without selecting others, such as markers.

	translate			objects mask
	rotate
	scale

In Actor Controls (which you can see if you click on Actor Controls tab in the Character Controls pane) you can turn on and off models (under Show), symmetry edits (under Edit), etc. Sometimes these are useful and sometimes they aren't. The images below show the actor before and after fitted into the marker data.

In Viewer, Ctrl+1 gives you a single perspective view. Ctrl+4 gives you four views (a perspective + three orthogonal views). Ctrl+Z is undo. Ctrl+Y is redo.

You will save out what you set up in this step and next step as a .hik file. The marker set (.hik file) will be used repeatedly to apply to Actor with other motions. This is extremely helpful because you don't have to go through this rather time-consuming step for every motion. Since you're using it repeatedly and since it will drive all of your motions, spend a good amount of time on this step.


Before	After	Reference

4. Creating a marker set. Once the actor is fitting within the markers, you'll need to make some arrangements as to which markers go with which section of Actor.

In the Navigator window, click on Actor under Actors. Actor Settings should appear. Click on MarkerSet... and select create from the drop down menu. (See the screen capture below.) You'll now see different areas representative of the head, torso, etc., with the number 0. You need to select markers in the Viewer and drop (Alt-drag) them into the correct locations.

	John's base marker set		UTD standard marker set
Section	No.	Names	No.	Names
Head	4	L_Front_Head, R_Front_Head, L_Back_Head, R_Back_Head	4	LFrontHead, RFrontHead, LBackHead, RBackHead
Shoulder	2	X_Back_Shoulder, X_Front_Shouder	1	XShoulder
Elbow	2	X_Outside_Elbow, X_Inside_Elbow	1	XElbow
Hand	2	(2 from wrist) X_Thumb, X_Pinky,	3	(1 from wrist) XWrist (2 from hand) XHandA, and XHandB
End	1	(1 from hand) X _Hand	0
Upper torso	4	Top_Chest, Low_Chest, Top_Back, Low_Back	5	Chest, TopSpine, LBack, RBack, MidBack
Hip	4	L_Front_Waist, L_Back_Waist, R_Front_Waist, R_Back_Waist	4	LFrontWaist, RFrontWaist, LBackWaist, RFrontWaist
Knee	2	X_Outside_Knee, X_Inside_Knee	1	XKnee
Calf	0		0
Heel	4	X_Ankle, X_Heel, X_Outside_Toe, X_Inside_Toe	3	XAnkle, XHeel, XMidFoot
Toe	1	X_Toe	1	XToe

Notes:

5. Exporting the marker set. Click on MarkerSet... in Actor Settings and select Export from the drop down menu (See the screen capture below). The marker set will be saved as a .hik file.

6. Activate the character. Activate the character by clicking on Actor in Actor Settings and play the animation.

7. Re-using the marker set. After you bring in a new .C3D file and a new Actor, import the .hik file that you saved out. To import a .hik file, click on MarkerSet... in Actor Settings and select Import from the drop down menu where you found create and export. Select ALL of the optical data points (including the optical root which is a green sphere), alt-drag, and drop them into Model part of the Reference section of the actor (See the screen capture below). Then MotionBuilder drops all the markers into the correct place. Click Active on and the actor should pop into place and move with your markers.


Before dropping markers	After dropping markers

Notes:

8. Character. When you are done with Actor, move onto the next step: Motion Builder: Character.

Modeling a 3D character. If you can let your 3D character have the proportion of the capture subject, do so because you will be required to spend less time on editing motions. Thus, if you need to match the motion of the capture subject to your 3D character that is proportionally different from the subject, you will have more editing to do.

If you can match 3D character's proprtion to that of the capture subject, do the following: Export marker data of a T-pose as a .fbx file from iQ (or MotionBuilder), import it it into Maya, and build your character's skeleton and skin using the data of the capture subject in a T-pose as a reference.

Also note that it is easier in MotionBuilder if all the joints are named using MotionBuilder's naming conventions. See the first step of MotionBuilder: Character.

Exporting a T-pose. A .fbx file is a few times bigger than a .c3d file of the same contents. To exporting a T-pose alone from iQ, instead of the entire Range of Motion trial, first select a few frames that contain a T-pose using the green start time marker and the red end time maker, go to File -> Export..., and select FIRST_SELECTE_FRMAE as Export Start Frame and LAST_SELECTE_FRMAE as Export End Frame in the options.