But as an example it’s easier to read without namespacing. Yeah, that’s my real excuse.

I understand a little bit about matrix math, but after carefully following your instructions to create the 4×4 matrix, I don’t understand how to use that matrix to get the Euler rotations that the constrained object needs to assume in order to aim at the target.

Could you help me understand?

Thanks so much,
Kirk

I’m typing this on my third new MBP (the second one that I got this morning I brought home only to find out that it had dead pixels!), and things are looking up, finally, so I don’t have to give up on Quicksilver just yet.

http://www.launchy.net/

I find that the number of points *does* in fact affect the result. When you have non-1V degree surfaces, you end up with less intuitive motion on the locator. It’s not about evaluation time, but rather about keeping the tangent vectors crossing each other in predictable ways.

By clustering a line of V cv’s and then rotating that line around the cluster, the path the U surface isoparms take through the surface becomes a bit skewed.

In the end as long as the rig doesn’t flip out and makes pictures, that’s all that matters; if you’ve had success with the normal constraint then I can’t say anything about that. I don’t use it because I haven’t had any problems with my method and since I know the surface normal is created from the cross product tangent U and V vectors, I like using the source vectors. The point of the post was that the rivet script which everyone uses can be improved upon, and that by using a script only as a black box of functionality you miss out on learning more about your software under the hood, as well as on potential fixes for poor behavior.

There’s something happening with the ” symbol here which prevents code from running when copied from this thread and pasted into a script editor on OSX. I had to run it through a plaintext converter to get it to work.

Anyway, your example works, but I was posting the above as an indicator of a situation of where it might not work, and a normal constraint would work a bit better.

Having a non-1 V degree won’t affect the result of either example. It’s true that using a smaller number of points is more efficient, but maya eats NURBS for breakfast…you’d need an incredibly huge ribbon before doubling the V CVs would make any difference in evaluation time.

Just because someone wrote it in a book, doesn’t mean it’s right!

I tried your code and tried plugging the .tv into the normalConstraint’s worldUpVector. I think I’m fuzzy on what you’re trying to accomplish.

From what I can see with your code, the reader object is behaving exactly as expected. Now, in your example I do get some perceived shearing when I set reader.posU to 0.84. Maybe that’s what you’re talking about?

The first problem I see here is that your V degree should be 1. It was either in the original Art of Rigging or the Farenheit DVDs, but for a ribbon to work well you need to keep the number of points down to a minimum. Here’s an example modified from your code. Scrub through the animation; you’ll see that the Z axis always aims out properly. Again there’s a bit of perceived shearing in extreme circumstances, but in my experience that shearing never adversely effects a rig using ribbons.

If that’s not what you mean, then I’m a little lost here.

file -new -force;

currentTime 24;
setAttr reader.posU 1;
setKeyframe "reader.posU";