Inverse kinetics?

I'm using the default SL man and woman avatars that are available for download here. You know, the bright green/blue ones. I like them, but I only seem to be able to move the hips naturally if I use inverse kinetics on the legs. If I turn off inverse kinetics, any effort to move hips results in unnatural gliding through space, and I'm not sure that gliding animates.

So I guess my question is: if one wants to move the hips in any direction, must leg inverse kinetics always be "on"?

The issue you're having is due to the fact that the hip is the root of the skeleton, as is usually the case for character models. When using forward kinematics (it is KINEMATICS, by the way, not kinetics), any movement to a joint also moves all the child joints beneath it in the skeletal heirarchy. Move the shoulder and the whole arm moves with it, for example. Since the hip is the root, it is the parent of the entire skeleton so any movement it is given will end up moving the entire skeleton as a whole.

When you have IK turned on, each joint behaves more independantly. Moving the hip won't necessarily move the whole skeleton since you haven't specifically told any other body part to move. Only those joints allowed to move by the IK chain will be affected. For example, move the hips down and the knees will bend, the ankles will flex, but the feet will remain rooted in place.

The answer to your question about whether IK needs to be on in order for hip movement to show in the SL animation is no, it doesn't. Move the hips up 10 meters, and your av will end up 10 meters off the ground (although it's a little tough to tell what a "meter" means in Poser in relation to SL). If you're using forward kinematics, and you want your av to shake her hips, you'll need to make sure that every time you move the hips you also put all the other joints back where they're supposed to be. Otherwise the entire av will move around as a whole.

Many thanks for your reply.

If you don't mind, a further question, just to check my understanding. If I want my avatar to turn around in place, I assume it is preferable to leave inverse kinematics "on" and to rotate the hips, perhaps switching IK off to adjust legs/shins/feet for any resulting weirdness after the rotation? With IK off, turning the avatar's hips about any of the three axes simply spins the avi as a whole, as if it were a mannequin being twirled about. Right?

Well, I'm not sure what you mean by "turn around in place." If you mean you want the av to spin as a whole, then the simplest thing to do is just turn off IK and rotate the hips. The whole body will turn in place without any individual movement of the joints, as if it were a statue standing on a turn table. If you want the av to animate the way a human being would as he or she is turning in place under his or her own power, that's actually a pretty complex animation. I'd recommend video taping yourself doing it so you can see exactly what a human body does in order to make that kind of turn. It's a lot more complicated than you might think. The body is always in a state of falling and catching itself whenever we take a step, and turning in place for a bipedal being actually requires quite a balancing act.

If you're doing the full animation, the question of whether or not to use IK depends on your personal style as an animator. Some animators find IK to be annoying or limiting, and somewhat unpredictable, while others find it to be a tremendous time saver. Personally, I usually end up using it to block out an animation in rough form and then I go back and tweak things using FK to make it more realistic and to fix any joints that end up ratating in weird ways, which is quite common with IK. The best animator I know in RL (who recently joined SL as Xenius Revere, by the way) will tell you he hates IK with a passion. He does absolutely everything with FK, his stuff is great, and he's able to do it at a very fast pace, which is really uncommon. Like I said, it just comes down to what method you prefer, IK, FK, or both, so experiment. (at least until motion capture suits become common place enough that we can all use them)

Yes, I meant turning the way a human being would turn, not spinning around like a statue on a turntable. Indeed I have spent some time watching videos of people walking, dancing, standing, sitting, and lying down. I have made my first few animations with .jpegs or .wmvs of similar poses/animations sitting in the background on my desktop. Yesterday I stared at a dance video over and over again for about an hour. Heh.

For me, IK seems to help me get the basics of movement right, but then I have to turn it off to tweak -- much the same process you described yourself using. For example, if I try to do a dance step, IK will get me from position 1 to position 2 in a plausible way, but it still won't look quite right: for example, the lead foot will move too smoothly. In reality, feet change speed constantly, or so it seems. In my dance animations, the characters either glide too smoothly or move too jerkily. Finding the right middle ground has been a challenge.

I suppose one should get into animations gradually, starting with easier stuff. I've made a few frozen poses; those are relatively easy, but they're not that interesting. Animated sits have come next for me; I seem to do better if I don't have to move feet around. And there seems to be a market for those. I just started work on my first cuddle; again, no footwork, and a decent market. My ultimate aim is to make couples dances, but wow, those are tough. Kudos to Jesse on his salsa animations.

Incidentally, where would I learn about "motion capture suits"? Or do you mean "suites"? Star Wars Galaxies apparently used motion-capture for its dances, and they looked pretty good. That is the gold standard of animation, I gather? Sensors on someone's body as they dance or move?

Uh, got somewhere between $10,000 and $100,000 to spend? That's what they cost. Anyway, to learn about them simply google "motion capture suit". You'll find tons of information.


Nope, SUIT - as in something you wear. An actor, stunt man, model, etc. wears a suit which is embedded with sensors that tell a computer where each of his or her body parts is at all times. That data is recorded and then applied to a 3D character model (such as an SL avatar). The model then precisely mimics the movement of the person in the suit.


Not suprising. Most big-budget projects will use motion capture rather than keyframing everything by hand. It's much quicker, and in most cases it's much more realistic.


Yup, for those who can afford it that is. Perhaps the most well known example is Gollum in Lord of the Rings. If you watch any of the behind the scenes stuff, you'll see the actor (same guy who did the voice, btw) prancing around in full-body spandex, covered in sensors.

There are of course animation houses that don't to use motion capture, like Blizzard Entertainment's cinematics department, which employs some of the very best 3D animators in the world. The cinematics for Diablo II, Warcraft III, and World of Warcraft are simply breathtaking, and unbelievably realistic. No motion capture was used for them other than video cameras. If you want some inspiration, I'd highly recommend getting yourself a copy of their DVD Collection. It's only $20, and it's really stunning. I'd also recommend downloading the World of Warcraft Intro Cinematic , which is simply the best piece of CG I've ever seen. (Download the AVI, by the way, and watch it full screen; the Quicktime version is too small to really give you the right effect.) Sadly there's no behind the scenes stuff available for that one, but the film itself is a must-see.

Thanks for your further reply. Actually, I beta-tested World of Warcraft -- yes, I was one of the lucky few -- and so I got to see that intro cinematic in various stages of development. As you say, it's a spectacular piece of work. And I've played all the other Blizzard games you mentioned too. In general, Blizzard's beta really wow'ed me, so to speak. I've beta-tested many other online games, but the professionalism of the WoW beta test was in a different league. Not surprising that the resulting game now has 4 million subscribers, making it the most popular MMORPG in history.

The current mysteries I face in animating for SL revolve around two problems, at least one of which may be related to the inverse kinematic of the thread title.

(1) Sometimes, for some reason, things won't animate, even though they move in Poser. E.g., I have a couch-repose in which a woman absent-mindedly moves her legs while tousling the hair of a guy who sits in front of the couch. She tousles fine, but her legs don't move. I think I turned off IK and just periodically bent her legs at the knee, ankle and occasionally foot. But I don't see any of this movement in SL.

(2) Male hands and arms seem to end up further apart than I set them in Poser. I assume this is because the size of male avis in SL is about a foot taller and wider than Poser anticipates, but I don't know. I suppose I should just try to compensate in Poser, but it's hard to force oneself make the male model put his hands in odd places. Or is there some other solution? I wonder if the downloadable SL avatar should be stretched about 10% in all directions...

Yeah, just too bad it's such a boring game. I was so disappointed. I've been the first in line at the store for every Blizzard game since Starcraft, so I got WoW the first day it came out (I wasn't so luckly in the beta test selection as you) and I played the hell out of it for the first month to see if it was worth contiunuing to pay the monthly fee for. I loved it for about a day or two, and then I got really sick of it (but kept playing anyway). Way too much running from place to place, way too little hack & slash, turn-based combat system just blows in my opinion. One hell of a cinematic though. I still watch it all the time for inspiration.


Hmm, did you perhaps not have keyframes on the leg joints when you exported the BVH? Or maybe the animation is not high enough priority. If so, it's possible the default sit animation is overriding you animation of the legs. Try re-uploading it again and setting it to highest priority if you haven't already.


That's a tough one. I haven't really found a good solution for stuff like that, other than trial and error. The poses I made for the box cover on my Firestar av, for example, took forever to get right. I was going for a couple of her dramatic poses from her comic book covers. Every time they'd look great in Poser, they'd look all wrong in SL, body parts angled all kinds of weird ways. All I could do was just keep making little adjustments in Poser and hoping for the best each time. I think it was a total of something like 27 uploads before I finally got one of the poses right. I never did get the second one the way I wanted it so I gave up on that one altogether.

I'm really hoping one day they'll incorporate this stuff right into SL so there won't be any need to farm it out to Poser. I think Daz Studio is open source (could be wrong on that). Perhaps eventually they'll pull from it for an inworld animator like they're currently doing from Firefox for the inworld browser.

Thanks once again. I'll check for keyframes on the joints. And you may well be right about the priority. I set it to just 3, thinking all I needed to do was override the typing animation. I keep reading that it's not polite to set one's animations to 4 or 5, though I'm not sure why that should be.

And your answer on hands is reassuring. I'm glad to hear I'm not the only one who just kinda uses trial and error. I guess I'd also favor an in-game tool; the selfish part of me thinks that might make animation a less sought-after skill, but the unselfish part recognizes that it would raise the quality of animation for all of us. Incidentally, I hadn't heard that about Firefox, my favorite browser; good news indeed.

We'll have to agree to disagree about WoW; I enjoy turn-based combat, and I found the quests and gameworld charming. I didn't mind the running; for me, it made the world seem more large and real, and in any case by level 40 I had a spiffy mechanical mount. I admit that the instant TPs in SL are nice, but one downside is that the geography of SL is pretty much irrelevant to gameplay. Most of the time, I have no idea where on the SL continent I am. But again, SL doesn't bill itself as a single coherent gameworld the way WoW does.