First, let me start by saying that I HAVE seen Rune's IK leg, and that while
it looks like a nice file, does not solve my problem.  I have a bipedal
system with legs consisting of a thigh and calf each 1.75 units, and a foot
.75 units long.  The model is manipulated by telling the joints a rotation
(I want the system to be as versatile as possible).  My problem is this: How
much and when should the joints flex?  I suppose I could figure it out, but
if anyone else has ideas, any input would be much appreciated!

Barron
If you give a man a program you will frustrate him for a day; if you teach a
man to program you will frustrate him for a lifetime; if you teach a Gates
to program you will frustrate the world.

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"Barron Gillon" wrote:
> First, let me start by saying that I HAVE seen
> Rune's IK leg, and that while it looks like a
> nice file, does not solve my problem.

I would like to help, but I can't if not you explain exactly why the IK leg
solution doesn't solve your problem.

> The model is manipulated by telling the joints a
> rotation (I want the system to be as versatile
> as possible).  My problem is this: How much and
> when should the joints flex?

The IK leg file can be used to find the angles if you really need them, but
I still don't understand what prevents you from using transformations rather
than rotations. They are equally versatile and walking will be much easier
when using transformations.

Rune
--
3D images and anims, include files, tutorials and more:
Rune's World:    http://rsj.mobilixnet.dk (updated Nov 5)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk

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Rune wrote:

> "Barron Gillon" wrote:
> > The model is manipulated by telling the joints a
> > rotation (I want the system to be as versatile
> > as possible).  My problem is this: How much and
> > when should the joints flex?
>
> The IK leg file can be used to find the angles if you really need them, but
> I still don't understand what prevents you from using transformations rather
> than rotations. They are equally versatile and walking will be much easier
> when using transformations.

I, too, preferred to set up a system where I kept my original "FK
construction",  used IK to program the position of the joints, then
back-calculated what FK would allow these IK coordinates.  It's more complex to
code this mechanism, but the simple FK construction is inherently pleasing to
me.

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"Greg M. Johnson" wrote:
> I, too, preferred to set up a system where I kept my original
> "FK construction",  used IK to program the position of the
> joints, then back-calculated what FK would allow these IK
> coordinates.  It's more complex to code this mechanism, but
> the simple FK construction is inherently pleasing to me.

But you cease to give me a rational reason, and so far the transformation
method has proven to be able to do the same and much more... :)

Rune
--
3D images and anims, include files, tutorials and more:
Rune's World:    http://rsj.mobilixnet.dk (updated Nov 5)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk

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Greg M. Johnson scribis news:3BF01FF8.2FAAC21C@aol.com:

> I, too, preferred to set up a system where I kept my original "FK
> construction",  used IK to program the position of the joints, then
> back-calculated what FK would allow these IK coordinates.  It's more
> complex to code this mechanism, but the simple FK construction is
> inherently pleasing to me.
> 
I have seen the term IK and FK used freely on this board. And though I 
understand that they mean Inverse Kinetics and Forward Kinetics, just what 
does that mean?

-- 
Gis posta, Arto.

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Arthur Flint wrote:
> I have seen the term IK and FK used freely on this board. And
> though I understand that they mean Inverse Kinetics and Forward
> Kinetics, just what does that mean?

Inverse Kinematics is a method wherein (since we're talking about
walking, I'll use a leg as example) you move the foot to its end
position, and everything that's attached to it (attempts to) move
appropriately.  Forward Kinematics is where you move each part
manually, i.e. upper leg is fixed at hip move knee relative to hip,
then ankle location relative to knee, then foot relative to ankle.
(Hear the word of the Lord!)

AFAIK, FK is what POV/Moray has.  Poser has IK as an option when
positioning arm/leg, but it's kinda funky because just moving
your foot doesn't take into consideration HOW you're moving your
leg.  It just does the simplest 'point B is the average of A and
C' construct (I think...).

-- 
Tim Cook
http://empyrean.scifi-fantasy.com

-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------

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First of all, they are both ways of positioning joints so the limb/body as a
whole is in the correct position, but their approaches to doing so are quite
different. In forward kinematics, you specify a rotation at each joint in,
say, an arm, to position the hand where you want it. In inverse kinematics,
you specify the location of the hand and the joint angles are mathematically
computed to place the had at that point.
Essentially, with forward kinematics:
Hip-moves-upper leg-moves-knee-moves-lower leg-moves-ankle-moves-foot.

With inverse kinematics:
Foot-moves-ankle-moves-lower leg-moves-etcetera.

--

//Mahalis
camera{location<0,0.25,-2> look_at 0.5*y} #declare T=texture{pigment{crackle
scale 0.5 rotate 90 turbulence 0.75 color_map{[0 rgb 1][0.05 rgb 1][0.1
rgb<1,0.25,1>][0.25 rgbf 1][1 rgbf 1]}} finish{ambient 1}} #declare
c=difference{torus{0.5,0.1 rotate -90*x}box{<0.7,0,0.2>,<-0.7,-0.7,-0.2>}}
merge{object{c translate<0.5,0.5,0>} object{c translate<-0.5,0.5,0>}
cylinder{<1,0.5,0>,<1,0,0>,0.1} cylinder{<-1,0.5,0>,<-1,0,0>,0.1}
cylinder{0.5*y,0,0.1} texture{T}}
--


"Arthur Flint" <mra### [at] chesapeakenet> wrote in message
news:Xns### [at] 204213191226...
> I have seen the term IK and FK used freely on this board. And though I
> understand that they mean Inverse Kinetics and Forward Kinetics, just what
> does that mean?

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Rune wrote:

> But you cease to give me a rational reason, and so far the transformation
> method has proven to be able to do the same and much more... :)

You may determine the rationality of this, but here goes:

1) My two complete and favorite blob systems were built with FK, so there's
no rewrite from scratch.

2) It's quite hard to model.  I came up with the perfect system using
transforms and spent a week making a blob out of it. It is hideous.

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Hi Timothy R. Cook, you recently wrote in povray.general:

> AFAIK, FK is what POV/Moray has.
Moray also has some IK functionality.

- Lutz
  email : lut### [at] stmuccom
  Web   : http://www.stmuc.com/moray

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Timothy R. Cook scribis news:3BF06018.5A563507@scifi-fantasy.com:
> Inverse Kinematics is a method wherein (since we're talking about
> walking, I'll use a leg as example) you move the foot to its end
> position, and everything that's attached to it (attempts to) move
> appropriately.  Forward Kinematics is where you move each part
> manually, i.e. upper leg is fixed at hip move knee relative to hip,
> then ankle location relative to knee, then foot relative to ankle.
> (Hear the word of the Lord!)
> 
> AFAIK, FK is what POV/Moray has.  Poser has IK as an option when
> positioning arm/leg, but it's kinda funky because just moving
> your foot doesn't take into consideration HOW you're moving your
> leg.  It just does the simplest 'point B is the average of A and
> C' construct (I think...).
> 

Thanks to both of you who answered. Now I can start to think about seetting 
up some form of posing system for the manniquins that I use.

-- 
Gis posta, Arto.

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