Proper way to do IK/FK matching?

[eek]

Ok the basics are this:

the fk chain at the elbow has a fake pole vector, to acheive this you do a linear interpolation between the wrist and shoulder based on the bone lengths (upper arm, lower arm) i.e if upper = 200 and lower = 100, you would do 1- (200/(200 + 100)) * upper + (200/(200+100)) * lower , then you project from this through the elbow at a maginitude of your choice.

Now the ik snaps to the fk, and the pole vector to the imaginary then the switch happens - a key at the time -1 is created of a value of fk = 100.0, ik = 0.0 then at the current frame ik = 100.0 , fk = 0.0.

Now to switch back the fk joints just match the ik ones and the switch happens again vice verse.

[DanHaffner]

Can you explain that a little more, I am really confused on what you were trying to explain. I do have the pole vector parented to the FK shoulder joint, that what you were saying about a fake pole vector, or are you literally saying I need a fake pole vector out there?

[Polimeno]

Ok the basics are this:

the fk chain at the elbow has a fake pole vector, to acheive this you do a linear interpolation between the wrist and shoulder based on the bone lengths (upper arm, lower arm) i.e if upper = 200 and lower = 100, you would do 1- (200/(200 + 100)) * upper + (200/(200+100)) * lower , then you project from this through the elbow at a maginitude of your choice.

Now the ik snaps to the fk, and the pole vector to the imaginary then the switch happens - a key at the time -1 is created of a value of fk = 100.0, ik = 0.0 then at the current frame ik = 100.0 , fk = 0.0.

Now to switch back the fk joints just match the ik ones and the switch happens again vice verse.

seems a nice solution eek, can you please post some pratical MXS code or a .max file ?

in a past solution/study, i did a match IKFK by tracking the transform of extra nodes (ie point_upper_ik/point_elbow_ik/point_upper_fk/point_elbow_fk) with weak reference,
where each one was place into the properly chain/bone with transform script.

DanHaffner,
take a look below :

http://seithcg.com/wordpress/?page_id=30
http://snolan.net/blog/ikfkArmSetup/ikfkArmSetup.html
http://www.macaronikazoo.com/download/zooToolBox.rar ...broken...
http://forums.cgsociety.org/showthread.php?t=469432

[DanHaffner]

Thanks for the links, checking them out now.

3rd link is broke.

[eek]

Can you explain that a little more, I am really confused on what you were trying to explain. I do have the pole vector parented to the FK shoulder joint, that what you were saying about a fake pole vector, or are you literally saying I need a fake pole vector out there?

ok so heres the basic math:

upperBoneLength = 100.0
lowerBoneLength = 100.0

shoulder = $shoulder.position
elbow = $elbow.position
wrist = $wrist.position

t = upperBoneLength / (upperBoneLength + lowerBoneLength) -- this is the ratio

fakePoleVector = normalize(elbow - ((1-t) * shoulder + wrist * t)) * magnitude + elbow

*magnitude is the offset from the elbow you want the fake pole vector to be. So basically i make a direction then i multiply it. This way its always a constraint direction from the elbow.

BUT and theres a big but. If both the upper and lower bones are perfectly straight then it'll break because theres no vectors to build a direction i.e they overlay each other.


One way to fix this is to instead of using the bone positions shoulder and wrist, you use two nulls, which are offseted from the bone, like so:

shoulder---Null
|
|
elbow
|
|
wrist------Null

[blackseraphim]

i suggest you use a blendColors node instead of constrains for the ik-fk blending.
1. create an ik joint chain
2. create an fk joint chain
3. create a bind joint chain
connect the IK and FK joint chains to the blendColors node and connect the output of the blendColors node to the bind joint.

create 2 locators
one locator (which will be the guide of the pole vector for the switching of the IK) parent/ point-orient constrain it to the elbowFK_Joint. name it elbow_guide
and the other locator would be the guide for the arm controller. name it arm_control_Guide
(parent/point-orient constrain it to the wristFK_Jnt)

writing for the script of the IK-FK switching:

from IK to FK
-get the rotations of the IK joints
-set the rotations to the FK controllers

from FK to IK
-get the position of the guide Locator(elbow_guide)
-set the translation values of the locator to the poleVector controller
-get the translation values of the of the arm_control_Guide
-set the translation values of the locator to the arm IK controller

*take to consideration the joint orientation of the joints because if not fix earlier in the setup, it will create a problem for the later setup.

hope that helps.

Peter

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