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Inverse Kinematics

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Hi guys - I have recently been looking into inverse Kinematics with a view to creating an animated crciket character to help with the coaching i do at a local club. I have quite a good understanding of maths but am a little confused at the moment. Anyway to start off with i was wondering whether any of you guys would be able to help me out with some refernces that could help me on my way to understanding what to do. Cheers in advance for any and all suggestions. Neil

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hi !

i recommend that you take a look into the CCD-algorithm if you are looking for a fast and easy to implement method. i used it for my IK-system to animate a human. the following paper might help you :

http://64.233.183.104/search?q=cache:JZWI6DlyjPkJ:crpit.com/confpapers/CRPITV35Merrick.pdf+ccd+algorithm&hl=de

or just google it..

hope this helps and good luck

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Guest Anonymous Poster
cyclic coordinate descent is one relatively easy but imperfect way to go, you can also use lagrange multipliers and have joint weights to promote more natural poses.

alternatively, ls-dyna (a very high end piece of engineering software) uses spring constraints for dynamic simulations. if you do the same but apply an attractive force between the effector and the goal and iterate until the effector and goal positions are the same, you should be able to incorporate joint weights and still get natural poses with relatively simple and fast code. i think the basic explanation for this is on a website titles 'gaffer on games' or something similar.

james

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Cheers for the input guys i'll have a look at all those things suggested but as an utter newbie may well be back looking for an easier grounding in the subject at a later date!!!

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Are you sure you are looking for the right thing? Your animated cricket character only needs IK if he needs to respond to an unpredictable environment (ie, lift his feet to climb stairs, or animate his elbows appropriately for incoming ball paths). If he simply needs to be animated, all you need is normal, forwards, kinematics, for which better search terms would be "skeletal animation".

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they do need to catch the ball, dive, or bat it properly. If you have slo-mo, IK could be cool and give a much more realistic feel.

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Quote:
Original post by Saruman
IK is pretty much a requirement for any good sports game/simulation.


Really? How so?

All the sports games I have worked on or looked at do not use IK unless they have to. IK is widley uncontrollable, hard to tune and ultimately a frustrating process to work with. Blending hand or motion captured animations is a lot easier and the artists get control.

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there was an awesome article on the use if IK on one of the Microsoft Mechwarrior game. I think it was in a Game Developper magazine (gamasutra / GDC affiliated). If anyone can find it, it was a very good resource.

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Iirc, the article in gdmag was just about animationblending lending itself well to IK, wasn't it?

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Been a long time, but I believe it was using IK, and blending IK into animations, not just pre-defined animation blending, as far as I recall. Anyway, good article, if you have a 1/2 decent IK constraints working.

Also, anyone noticed some IK in Half Life 2? I've seen that happening when I jammed a barrel underneath Alyx's feets, and the legs went a bit crazy.

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No... If there's IK in there, it seems kind of unstable :) I thought they were just using ragdolls with constraints and some animationblending...
But i haven't looked very carefully at it, and it was a while ago sice i played it :)

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Quote:
Original post by oliii
there was an awesome article on the use if IK on one of the Microsoft Mechwarrior game. I think it was in a Game Developper magazine (gamasutra / GDC affiliated). If anyone can find it, it was a very good resource.


The article about mechwarrior was very specific about overcoming the need of IK by using animation blending. They used a four axis animation blender that could blend between the rotation of the leg walking on certain angles to give the correct alignment of the foot to the ground plane. They specifically cited that it would be unrealistic if not impossible to accurately create IK given the number of simultaneous entities they had to tune for.

I also can´t find it but it is a good read on gamastutra.

- S

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Cheers guys - it so happens that that is one of the first articles i looked at in researching this topic as a possible angle for some work.

However at the moment the hard thing is finding a worked example that i can apply to what i want. I have some now however and will continue looknig at those that you have sugested.

Cheers

Neil

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