TheUsualAlex Posted July 17, 2002 Share Posted July 17, 2002 Hi guys, May be I am just the only one who don't get it... Is anyone of you willing to provide me an example of a working Particle CHOP? I just don't understand how to get this to work at all after reading through the CHOP manual. Also, what is Quaternion and Time Slice? What is their function? THanks, guys. Quote Link to comment Share on other sites More sharing options...
danteA Posted July 17, 2002 Share Posted July 17, 2002 I think the Particle CHOP is used for RBD. Try looking at the docs for how RBD works. Time Slice mode in CHOPs means to only generate data at the current frame I think (as opposed to generating the data for the entire length of the animation). Quaternion is an alternate representation to 3D rotation angles that are free of gimbal lock. You can think of it instead as an "angle & axis". ie. an angle value rotated around an arbitrary axis. You might be able to experiment with how an "angle & axis" type of rotation works with the TransformAxis (sp?) SOP. dante Quote Link to comment Share on other sites More sharing options...
TheUsualAlex Posted July 17, 2002 Author Share Posted July 17, 2002 I think the Particle CHOP is used for RBD. Try looking at the docs for how RBD works. Ah! No wonder I couldn't get it to work. Now that you mentioned it, I just remembered something about this back in the v4 tutorial guide. I'll have to take a look there. THanks! Time Slice mode in CHOPs means to only generate data at the current frame I think (as opposed to generating the data for the entire length of the animation). I would supposed that this would require a little bit more cpu resources as it is required to generate data at current frame? What is the advantage of this over pre-generated data like keyframming? Or rather, in what kind of situation would time slice be advantageous? Quaternion is an alternate representation to 3D rotation angles that are free of gimbal lock. You can think of it instead as an "angle & axis". ie. an angle value rotated around an arbitrary axis. You might be able to experiment with how an "angle & axis" type of rotation works with the TransformAxis (sp?) SOP. I see. So this is basically similar to how Houdini's tumbling works? Thanks, Dante. I'll take a look at xformAxis SOP. Quote Link to comment Share on other sites More sharing options...
danteA Posted July 17, 2002 Share Posted July 17, 2002 Woah ... I was kinda off base on the Time Slice thing. Apparently, it does something like cooking and keeping only the last X samples of data around while the playbar is running. This means that for large CHOP networks, you can get very good interactive speeds for stuff like the Spring CHOP. Quote Link to comment Share on other sites More sharing options...
Jason Posted July 17, 2002 Share Posted July 17, 2002 If you look at the script recently submitted to odforce for a switching IK/FK setup, you'll see a little better what the Quaternion CHOP does. It reads rotations and creates a "CHOP Attribute" called "quaternion" out of them. This makes rotations then being fed into the Composite CHOP blend accurately and smoothly. It's the first use of the Quaternion CHOP I've ever seen, and it seems to work great. Cheers, J Quote Link to comment Share on other sites More sharing options...
sirogi Posted July 17, 2002 Share Posted July 17, 2002 about Quaternions.....(ok, picky math people cover you ears....I'm just gonna give shreds of knowledge, by no means holy or accurate...) it's a fancy name for a math model that links rotations in all 3 axes so you get all your rotations described in one handy matrix. (ok, regular rotations can also be translated in a matrix, but that's another story ) the key thing to remember that rotations are applied *simultaneously*... as opposed to specifying separate roattion channels for x,y,z.... the reason for this is, you've probably noticed in a lot of transform tiles (eg: the transform Sop) you have to specify in which order to apply rotation to the axes (RxRyRz, or RyRxRz, etc...all permutations...) why is this an issue?...because you can have a case where the rotation applied to one axis (say, Y) would align the X and Z axes.....that would cause what is called Gimbal lock (www.google.com -> gimbal lock -> gotcha! ) ......and that would be bad for subsequent rotations (jitters, snaps and the ilk...) Hence quaternions being used to interpolate rotations smoothly from one "pose" to the other..... why aren't quaternions used all over the place? simple my little man, they're not as intuitive as telling each axis what to do..... ok, math people...you can come out now.... just my 2c. Quote Link to comment Share on other sites More sharing options...
Stremik Posted July 18, 2002 Share Posted July 18, 2002 2x2=5 Do I qualify for one of the math people? Anyway. It was cooool man! Thanks for the lesson! Quote Link to comment Share on other sites More sharing options...
sirogi Posted July 18, 2002 Share Posted July 18, 2002 you're welcome.... actually this guy is much more articulate: http://www.anticz.com/eularqua.htm ...but says the same thing Quote Link to comment Share on other sites More sharing options...
anakin78z Posted July 19, 2002 Share Posted July 19, 2002 Hi, I'm a little drunk right now, but I felt like adding to the conversation. While Charly Brown (nah, nah, I know the guy... not being mean!) did a wonderful job of explaining Quaternion stuff, I hope I can shed some light on Time Slicing... I use it whenever I don't want everything to start over on frame one, and I don't want an animation range that's a million frames long. It's fun for interactive stuff, that doesn't really depend on frame range (like building a space flight simulator in houdini. You shoudl try it! Come to think of it, that quaternion stuff would have come in handy there too!) Anyhoo, say you have a keyboard chop, a record chop, an area chop, and for some reason another record chop (I told you I was drunk!), and you're doing all sorts of fun stuff with them. Once you get back to frame one, all restarts, and you're not happy. But, BUT!!!, if you turn on time slicing in the area chop, suddenly the magic happens, and at frame one, you are overcome with joy, as you see that it does not reset, but indeed continues where it ended, as though there was no end, and no beginning. Wow.... that's almost like, deep, and stuff. Oye. Me go sleep. Cheers! Snej Quote Link to comment Share on other sites More sharing options...
TheUsualAlex Posted July 20, 2002 Author Share Posted July 20, 2002 Thanks folks, I will definitely take a look at it and experiment them. So... "I'll be back." ( ) Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.