Folks,

I've gotten the first version of my Expressions Tutorial put together. I am still working on some 'secret sauce' type formulas that do neat tricks.

I've tried to treat the math as generally as possible, while providing lots of examples that will hopefully get things cooking up.

http://www.prism.gatech.edu/~gtg724n/math.html

Enjoy and post questions, confusions or whatever comes to mind.

Bjorn

Awesome stuff Odin!

There is so much to get my head round there - but in a good way. The only thing missing is the sound of chalk on a blackboard and the smell of a dusty classroom!

I really hope this takes off.

Bjorn,

We've been asking for more information on expressions and boy are you delivering!

Thanks to your efforts I'm starting to wrap my brain around some of the basic concepts and it actually seems to be sticking in my head!
Never actually thought that could happen!

Bravo to you Sir!

Bjorn,

Thank you very much! I'm looking forward to the "secret sauce" tricks.

Good work Bjorn! Please post more as you can!
Mike Fitz
www.3dartz.com

Great stuff Bjorn! Just when I'm needing to learn about it too!

I'm trying to get a ball to turn when it's pushed in any direction on the ground. I guess it would be something like linear motion=turning motion....or something haha! I'll have to look over that tut again!

Yeah - that's a good one Ken. That's one of the secret sauce bits, but I'm trying to make it happen for a cart - still having trouble figuring out where to get information on the tire's travel, though. I've got it working in a straight line, but nothing happens when the cart is turning - still a couple of math tricks left that I can use on it, though.

For the ball (I guess this should be another general expression to use):

Arc length is 2*pi*angle, where the angle is in radians. The length the ball travels on the ground must be equal to the arc length it rolls along (assuming no slippage). So with a little algebra:

Angle = distance / (2*pi)

Of course, now all you have to do is figure out which axis of the model bone goes with which angle, which isn't always easy to do right away, let me tell ya

Edit: Sorry, I'm getting things messed up with this whole radian/degree duality that the expressions use. The real formula:

radius*angle (in radians) = distance

Converting to degrees and solving:

angle = distance / radius * (180 / pi)

This tute should have a big header stating "Great Place for Beginners to Start". heheheh. or "Noobies Only" hahah. I'm such an earhole.

One small mistake I noticed (and corrected) that I want to make a clarification on here:

The driving Rotate channels (i.e., if Rotate.something is on the left hand side of the equation) all work in Euler degrees.

The functions like cos, sin, tan work in Euler radians.

The driven Rotate channels (i.e. Rotate.X, Y, Z and W) work in Quaternions by default or whatever else you choose to make them.

A little confusing, yes, but each of these formats has its own special purpose.

My head is still spinning. It's kind of funny, I'm supposed to be learning this stuff in geometry, but this is confusing.