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xerzi
06-25-2011, 02:43 AM
I am currently making animations and I was wondering if anyone could offer some insight and possibly some reading material on IK points that helped them. I am wanting to do something basic such as having both hands on a spear at all times. When I begin to blend animations the hands tend to lean off the and clip with the spear. I have two points selected on the sphere a long with joint data, socket, hinge, etc... but I'm not sure how to apply it. Thanks for any help.

Alfonse Reinheart
06-25-2011, 11:08 AM
The general idea to fix your problem is fairly simple. When you build your animation data, you get the positions of the hands relative to the spear, not relative to the upper arm or forearm or wherever. That way, when you blend the positions, they are not likely to significantly move away from the spear.

Now, you don't technically need IK. If you don't use IK, then the error will manifest as slightly shrinking the forearm. This is far less noticable than hands drifting away from the spear, so you can probably get away with it. But, if you feel that it's still too much error, you can check this page out (http://www.webdesign.org/3d-graphics/tutorials/how-to-use-the-two-bone-ik-solver.3397.html) on 2-bone IK solving.

xerzi
06-25-2011, 01:25 PM
I was looking more for the mathematics behind it. Sorry that wasn't the best example. I need the math behind IK points as I'm generating certain animations, such as the acceleration and deceleration of a car, the person in the car to move forward/backward left/right depending on how the car is moving. I want the hands anchored to the steering wheel so when I blend the acceleration animation when the car starts to move, the hands move off the steering wheel and clip with the car. As well when the car starts to steer left/right the wheel also moves which is an animation of the car and not the biped it would be easier to just anchor the hands to steering. Sorry for the confusion.

Alfonse Reinheart
06-25-2011, 01:44 PM
I didn't realize that the link in question didn't have math in it. I saw something that looked like an equation, so I figured it was the math. Here is a series of articles (http://www.ryanjuckett.com/programming/animation/16-analytic-two-bone-ik-in-2d) showing the 2D math for two-bone IK. To do it in 3D, you need to apply a "spin" rotation along the axis between the two fixed points.

The spin to use is something of an artistic issue, since it could be virtually any angle. A good place to start would be to compute what the spin would have been from the regular animation and just use that.