PDA

View Full Version : Problem with bone setup



Dick Ma
11-29-2007, 10:43 AM
Hi,

I have a problem with the following bone setup. Please see attachment.

I cannot have the lower two pair fo bones to do correct "Point to target" With the default tool or using Relativity.

Can somebody figure out why or is it a bug that is cannot solve?

adamredwoods
11-29-2007, 03:40 PM
The Long Answer:
Lightwave animation is not robust. Lightwave does not record and utilize cummulative heirarchy position, rotation, and scale after a Target Item or Motion Modifier has been applied. In other words, you cannot set World Coordinates to your object, but you can read them. An object is set using relative coordinates to its parent. SO, in order to set an absolute position for your object, you'll need to know every object's position and rotation and scale in the heirachry and add it cummulatively to your object. Sometimes you can get around it, sometimes you can't. Positions you can add cumulatively, but rotations, no way. Matricies or quaternions.

The Short Answer:
Your'e stuck. In your specific example, the further down a heirachy you go, the worse the data is going to be. Notice that RLeg3 and beyond will have the wrong information set in motion modifiers. It can read ok, but not set. Why does the line connect the two bones correctly? Because the line is drawn(set) using absolute positioning. But not so with motion modifiers. So any motion modifier used will set using the wrong info. If you parent the questionable bones to bones higher in the chain, it will work, but that's not what you want.

This is a core problem to Lightwave's animation (which I've been working on my own solution to... see RigMaster).

Relativity works better than Target Item. For an example, try this:
Using two bones parented to an object, create two Nulls, not parented. Target one bone to a null, and the other bone to the other null. If you animate the nulls you'll see inaccurrate feedback using TargetItem. Relativity does better, but you don't get the instant feedback. To screw up Relativity, now parent a null to one of the bones.

SplineGod
11-29-2007, 08:57 PM
Actually thats not the problem. The problem is That Dick used Match Goal on the end of the IK chain. If he turns it off the relativity stuff after that should work fine. Anything using match goal doesnt allow its rotational values to be seen or referenced.

Dick Ma
11-29-2007, 11:35 PM
With the Match Goal Orientation is off, well the point to target stuff is correct, but the leg rig setup is weaken a lot.

Well if it is a simple character leg rig, yes it works good but now...

SplineGod
11-30-2007, 12:13 AM
There are other ways to get the same effect as match goal. :)

Dick Ma
11-30-2007, 09:14 AM
Regarding to the bone to target issue, I think it is a bug...because if there is a hidden line that able to point to the target, why the bones can't do that so?

And when I check the old scene that created by old version of LW, the result is correct, by looking at the render result (actually I would like to re-render some of my old files by renewing the shaders.. now I can't)

adamredwoods
11-30-2007, 12:02 PM
Thanks for spotting the correct answer SplineGod.

But my long answer does acknowledge why MatchGoalOrientation doesn't share rotation values with other motion modifiers. Which is starting to get frustrating for those past the basic setups.

SplineGod
11-30-2007, 03:40 PM
I use matchgoal on simpler setups. If I need to reference a channel with an expression etc Ill use another method. There is a 3rd party matchgoal plugin as well. Also I tend to not worry about things like pistons etc which are incidental to the actual character animation until after Ive gotten the base animation working. You can use something like DSTorms IK baker when done animating and then you wont have to worry about some things not reading IK controlled channels.
These days I typically rely on IKBoost. I can lock the orientation easily and I never have to worry about expressions and motion modifiers not working with IK because IK and FK within IKBoost is always interpreted as FK. IKBoost doesnt use Goals but always applys motions directly to the bones.