For applications where the Alias model matches the talent in size, limb length, and so on, use the Mimic Solution for arms and legs. Since the model's size is the same as the talent's, Mimic should generate correct rotations for knees and elbows, and match the end effector positions better.
| Don't forget to enter offset positions in the calibration deck for the elbow and knee offsets from the sensor as described in "Calibration of the Motion Sampling" earlier in the MotionSampler chapter. |
Use an Offset3 filter between the Position output from Biped2 and the input for the DAG node where you are applying translations. This filter can be used for two purposes:
If your model's legs have different joint lengths from your talent, you`ll find that the feet don't stick to the ground very well. There are two indications of this:
The following assumes that your model is different enough from your talent that you are using the Reach Solution mode, although the general concepts are also applicable to Mimic.
If the feet slide on the floor, the talent's translations in X and Z are moving the model either too far or not far enough during a stride.
The X and Z scales should be the same values in all cases, although the Y value may vary somewhat from the other two.
| As a general rule: |
| If the model is smaller than the actor, the scales for X, Y, and Z should be less than 1.0. |
| If the model is larger than the actor, the scales for X, Y, and Z should be more than 1.0. |
There is a relationship between the limb scales for the leg and the translation being applied to the model, and some adjustment of both values is necessary.
Adjust the leg scales so that the timing of the knee bending matches what the actor is doing.
You may also need to make adjustments to the Y rotation of the leg sensors to adjust the sensitivity to the actor's knee bending. Since the sensor placement is almost always not perfectly straight up and down in global space, a rotation adjustment is usually required.
Placement of the Back sensor is critical to getting good movement, especially for leg motion. You want to get the sensor as low on the actor's spine as possible while maintaining the actor's comfort as much as possible.
The main problem with this sensor is that when an actor bends at the waist, a sensor that is placed too high picks up these rotations, changing the local orientation of the hip offsets. The more rotation picked up, the worse the problems with calibration become.
| The hip rotation is more properly applied to the back or spine joint. |
As there is no perfect place for this sensor, there will always be some error due to this problem. At Windlight Studios, we use a mountain-climbing harness with a plastic plate, which extends down to nearly the crotch height in the back. This gives a firm anchoring location for the sensor that also flexes somewhat.