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BeeVee
10-14-2005, 09:29 AM
Hey all,

We've just put up the first part of a fantastic rigging tutorial by Kevin Phillips (Kevman here). You can get to the tutorial in English or French here:

http://www.newtek-europe.com/uk/support/tutorials/index.html

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GruvSyco
10-14-2005, 02:39 PM
Thanks for that Ben... not bad.

The tutorial I wish someone would write on rigging is one that actually explains how rigging in LW works and why things are done the way they are. I tired once to make a simple 3 bone rig to try and figure out the dif between IK and FK and where and how to add nulls... no luck what-so-ever.

Most of the rigging tuts out there are pretty specific to biped character animation... and just walk you through... put this here, rotate this, set such and such a value, reset this.

Please man, if you have any pull... find the guy that can actually explain this stuff!

BeeVee
10-14-2005, 03:06 PM
Hopefully Kevin himself will reply to this thread and of course we can add an explanation to his series (perhaps a chapter 0?) if he's willing to write it, but a simple request of "What is IK?" is probably too nebulous. I can tell you the difference at a basic level: FK or Forward Kinematics is where you work from the base level outward. Imagine a GI Joe figure. Although his arm is articulated, when you rotate it from the shoulder you need to rotate the arm about the elbow, then the wrist to get the hand where you want it. That is how FK works. Now, IK on the other hand (no pun intended) would be where you hold the GI Joe's hand and a) stretch it out to full reach and b) move it downwards so that it's by his waist in the same motion. You'll notice the bend at his elbow straightening out and that the shoulder rotates to facilitate the hand being at his side. That's (kind of) IK.

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richdj
10-14-2005, 03:13 PM
BeeVee,

That has got to be the easiest way I've heard IK/FK being explained... I just wish thats how it had been explained the first time, it just makes it so easy...

Rich

Oooh, excellent tute from Kev....

GruvSyco
10-14-2005, 03:14 PM
Now, IK on the other hand (no pun intended)
Cute.. I actually smiled at that!

Okay... so, to try and make this a productive discussion on rigging in LW... Why would someone use IK over FK or FK over IK? What are advantages to either for animating? That's a start.

ursa
10-14-2005, 03:22 PM
Ik is useful for keeping things attached to something (like a hand to a glass or a foot to the floor), whereas Fk is more controlled and works more like our bodies do (the down side is that you have to keyframe everything).

kevman3d
10-14-2005, 03:47 PM
I think that Ben's IK explanation says what you need to know - IK is pretty much just that - Move either end of the arm and the arm bends to stay connected to each end (bending the elbows, etc)

Basically, it works like a chain - Hence why you'll hear it referred to as an 'IK Chain'. A chain has a start and end where - Lets say for sake of an example that the chain is a real one, made of metal links and forms a fence - It's ends will be the wooden posts at each end.

Now, if you move the ends of the chain - Unhook one end of that chain and move it around... What happens to the links? They rotate and fold up into each other, right.

So, the same can be said of IK - You move one end of the 'chain' (say the hand) and the links (the joints in the arm/leg/tentacle/etc) need to rotate so that they still meet the ends of the chain (usually the shoulder and hand).

That's just another way to 'look' at IK - However unlike our realworld analogy with its gravity, friction and other environmental influences, LightWave's has to be mathematically calculated which is not always 100% perfect, but reasonably good enough to simulate things like limbs on a character.


As for why use IK and FK?

That's Simple - It all depends on what you are animating. :D

As a general rule, I will use IK for anything where the ends need to stay 'attached' or at least, attempt to stay attached to a point. The best example of this is obviously the legs of a character.

The weight of the character, and gravity holds your feet onto the ground - So it you lean sideways, your feet stay flat on the ground while your legs bend...


IK is PERFECT for this kind of thing - FK is not perfect, since you'd bend your character, then have to hand-keyframe the legs and feet to make them appear to be stuck to the same spot on the ground. That's not easy - You'll see this problem in old animation before IK became a standard tool of choice - Feet that appear to slide or 'iceskate' across the ground, etc.

Now, feet are not the only thing - Other places where IK could be useful - Hands that stay sitting on the arms of chairs - For example, say your character was sitting in a chair, but then needed to lurch forward to scream at another character - If you IK the arms, you can leave his hands on the arms of that chair, and when he lurches forward, his arms will bend automatically.


FK on the other hand (Definitely NOT a pun! :D ) I often use in arms that need to be fully articulated (where a character is gesturing) - FK means YOU control the rotation of things, and YOU have the power to pose and tweak them as you want them.

Obviously, this means more work, but it all depends on how you like to animate and just how artistically 'picky' you are over the exact poses you want from your objects.


Often you'll see IK/FK blending options added to Maya rigging - Most of the time its not always because someone wants to IK pose then FK 'tweak' something (but its possible there are some people that DO pose then Tweak, so don't quote me on that) - Its also because the rig will be delivered to more then one artists, and some artists prefer FK over IK, so giving users two options is good in a team environment.

Of course, sometimes it may be interesting to be able to blend a percentage of FK and IK together to fine tune a mesh, but honestly, I've never found the need for it where I tend to mostly do a lot of FK pose based animation anyway. But that again is just my choice... Its not everybodies...


BTW - LightWave has a great tool called 'IK booster' that gives you a great way to FK/IK stuff (but its not intuitive for most new users). Its definitely a great tool to look at learning imho.

I can't recommend Larry Shultz's intro videos for this tool enough! ( http://www.kurvstudios.com/lightwave/ikbooster.php ). He makes it a lot clearer and easier to understand - Worth the investment of US$24.95

cresshead
10-14-2005, 03:58 PM
also another analogy for ik as opposed to fk is if you think of ik as puppeteering...either with rod or strings attatched to the character extremities such as hands and feet...

also many new users don't know what ik or fk actually stand for...

fk:- forward kinematics
ik:- inverse kinematics

One of the most useful tools in producing computer animation is the ability to link objects together to form a hierarchy. By linking one object to another, you create a parent-child relationship. Transformations applied to the parent are also transmitted to the child object. By linking more objects to both parent and child objects, you can create complex hierarchies. Chains can be created to include ancestors (parents' parents) and descendents (children's children).

Kinematics describes the movement of the chains. They can be animated by transforming the parent object (forward kinematics or FK) or by manipulating the other end of the chain (inverse kinematics or IK). Forward kinematics is primarily based on rotational keys; inverse kinematics is based on translations and rotations of special manipulators (goals and end effectors) which drive the ends of the chains.

SplineGod
10-15-2005, 12:59 PM
Thanks Kev! :)

Gruvsyco,
Ive also got a complete course on rigging...about 21 hours of material at this point. It explains it all in great detail.

My 2cents on IK and FK.

FK is what you do in stop motion animation. As Kev said, its advantage is that you have absolute control. Its disadvantage? You have absolute control. Its not the quickest way to animate.

IK is what you would do with a muppet or marionette. You animate from the end of a limb back to the root. Its advantage is speed or when you need things to stick so a surface or item. The disadvantage is the lack of control that FK gives. Sometimes IK animation can look 'floaty'.

Its more difficult with IK to get joints to 'break' from the root out like a real lanky arm on a character with a slow, lazy walk. That by definition has to happen from the root on out (FK).

Some people like to use IK on the lower body and none on the upper. Some like to use IK as a quick way to 'block or rough out" the animation and then fine tune with FK. Some ppl like to be able to blend between the two on the fly. You can animate using IK in LW then bake it and tweak the final animation using FK. When you bake the IK motion becomes like mocap and the IK is turned off. The baked motions can be filtered in the graph editor to make it easier to edit. Its also possible to turn on IK again to redo something and then rebake.

The method you choose will also drive how you rig your character. There are many ways to rig and sometimes a rig can become quite complicated. I like to keep my rigs simple.

Theres also two parts to rigging:
Rigging for animation
Rigging for deformations.
The two arent necessarily related.
Rigging for animation focuses on getting a rig that provides fast feedback, is poseable, its stable between poses and is FUN to use. Nothing is more frustrating then posing part of a rig and then having it break the pose as you tweak with other parts of the rig. Its also frustrating to see a rig wig out in between key poses.
Deformation are something I try and worry about separate from the animation part. I try and make the deformations work with the animation. Mixing both at the same time results in poor feedback and increased frustration. Workflow is very important here.

Its also important to understand that being a good rigger depends on how well you know and understand the animation process. The more you know how to animate the better youll be able to rig. If you cant animate then find someone who is an experienced animator that can try and break your rigs and give good feedback. :)

kevman3d
10-15-2005, 03:38 PM
...and is FUN to use. Nothing is more frustrating then posing part of a rig and then having it break the pose as you tweak with other parts of the rig. Its also frustrating to see a rig wig out in between key poses.

That's an EXTREMELY good point - If you find a rig hard to animate, you're gonna hate animating. Simple as that...

The most fun I've had animating at work is when one of the guys rigged up a character that was brain dead to work with, and deformed perfectly. That's when your work goes from 'work' to 'can this really be considered work?' status! :D

Thanks Larry - That's really some Great advice (as expected from one of the best! :thumbsup: )


Kev.

colkai
10-16-2005, 03:28 AM
FK is what you do in stop motion animation. As Kev said, its advantage is that you have absolute control. Its disadvantage? You have absolute control.
Boy, I love that quote! :D It couldn't be any simpler, or any more true. :thumbsup:

WilliamVaughan
10-16-2005, 02:01 PM
Thanx for everyone involved in making this happen....it's always cool to see community support like this!

jasonwestmas
10-18-2005, 12:43 AM
Wow, this stuff is great! I've just recently started using IK booster. Amazing flexibility despite it's few limitations I've read about. I noticed it was possible to rotate and key the bones (FK) while keying the IK booster handles in a biped character. Is this a bad idea? I haven't thoroughly examined this feature yet and I'm wondering if I could get some advice.

Thanks everyone!

SplineGod
10-18-2005, 01:10 AM
I think some of the limitation perceived in IKBoost are sometimes that the proper way to use it isnt understood. IKBoosts IK is part time which means you can use FK and IK interchangeable. Use both if its working for you. The idea is to get a good performance out of your character. :)

jasonwestmas
10-18-2005, 10:02 AM
Awesome tutorials on your site SplineGod! Definately helps me understand what is possible in LW8. I'm glad to hear that FK is compatable with IK boost without having anything break on you. Coming from LW7 I had to break a lot of rigs to get the performance I was after.

Another cool thing about IK boost is that I no longer have to bake my IK computations into the bones to import the animation into Deep Exploration. I'm not really sure why that is but it's mainly because all the bones are set to keyframes in the motion properties panel when using IKB.

SplineGod
10-18-2005, 02:24 PM
You can easily switch between IKB style animating and LW style on the fly. The keyframe data is fed right into the graph editor as usual. IKB can be enabled and disabled as you go with no ill effects as well. :)