gdalgorithms-list

RE: [Algorithms] Skeletal Animation...

[Tom F. <to...@mu...>]

Use stiff springs between the vertices of the ponytail, and no instant
propogation down the chain. So each frame, each spring just affects the ones
it is attached to. It works just fine for apps like this, where a little bit
of deformation is not going to be noticed. Propogating forces/impluses down
chains instantly is a real pain, but allowing the springs to do it
themselves over a few frames makes life much easier. It goes wrong for some
apps, but not in this case.

Tom Forsyth - Muckyfoot bloke.
Whizzing and pasting and pooting through the day.

> -----Original Message-----
> From: Brandon Moro [mailto:the...@us...]
> Sent: 29 August 2000 06:59
> To: gda...@li...
> Subject: [Algorithms] Skeletal Animation...
> 
> 
> Hello.
> 
> I was wondering if anyone had links to some good skeletal animation
> techniques and perhaps some information about the kinematics involved.
> 
> For example, if I was a model to have a ponytail which moves 
> realistically.
> Given gravity and the mass of my character, I should be able 
> to generate the
> normal force produced by walking (feet hitting the ground).
> 
> Assuming the ponytail is just a couple bones end-to-end 
> sharing intermediate
> vertices, the problem I arrive at is the way to correctly 
> propogate a force
> applied at the origin vertex (ie the one connecting the 
> ponytail to the
> head) down into the other vertices.
> 
> Any possible links would be great.  I heard that someone 
> wrote quite a few
> papers on the physics involved in this, but I can't remember his name
> exactly.  I know his last name is something like Mirich, but 
> thats not quite
> it.
> 
> Thanx!
> Brandon Moro
> 
> _______________________________________________
> GDAlgorithms-list mailing list
> GDA...@li...
> http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list
> 

Re: [Algorithms] Skeletal Animation...

[Frag_ D. <fra...@ho...>]

     Wow, Jeff Lander's on this list!  How did I miss this list for so 
long!?!  Anyways, I've been reading like twenty-thousand emails, and am very 
glad that I joined this list.  Just wanted to comment on it...


>From: Jeff Lander <je...@di...>
>Reply-To: gda...@li...
>To: gda...@li...
>Subject: Re: [Algorithms] Skeletal Animation...
>Date: Mon, 28 Aug 2000 20:49:18 -0700
>
>
>Has Game Developer got some issues for you.  I have written several 
>articles on deformation of a mesh using an imbedded skeleton.  That will 
>handle the rendering aspect of a kinematic animation.
>
>http://www.darwin3d.com/gdm1999.htm#gdm1099
>http://www.darwin3d.com/gdm1998.htm#gdm0598
>
>For the physics, Chris Hecker wrote a multi-part series on linked rigid 
>body dynamics.  Specifically the example was a ponytail that moved 
>dynamically connected to a kinematic head.
>
>www.d6.com
>
>I don't know if Chris posted his ponytail app yet but if he hasn't send him 
>a note bugging him.  It should be there :)
>
>The person you were thinking of is Brian Mirtich from MERL.  His website is 
>http://www.merl.com/people/mirtich/
>
>-Jeff
>
>At 10:58 PM 8/28/2000 -0700, you wrote:
> >Hello.
> >
> >I was wondering if anyone had links to some good skeletal animation
> >techniques and perhaps some information about the kinematics involved.
> >
> >For example, if I was a model to have a ponytail which moves 
>realistically.
> >Given gravity and the mass of my character, I should be able to generate 
>the
> >normal force produced by walking (feet hitting the ground).
> >
> >Assuming the ponytail is just a couple bones end-to-end sharing 
>intermediate
> >vertices, the problem I arrive at is the way to correctly propogate a 
>force
> >applied at the origin vertex (ie the one connecting the ponytail to the
> >head) down into the other vertices.
> >
> >Any possible links would be great.  I heard that someone wrote quite a 
>few
> >papers on the physics involved in this, but I can't remember his name
> >exactly.  I know his last name is something like Mirich, but thats not 
>quite
> >it.
> >
> >Thanx!
> >Brandon Moro
> >
> >_______________________________________________
> >GDAlgorithms-list mailing list
> >GDA...@li...
> >http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list
>
>_______________________________________________
>GDAlgorithms-list mailing list
>GDA...@li...
>http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list

_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

Share information about yourself, create your own public profile at 
http://profiles.msn.com.

Re: [Algorithms] Skeletal Animation...

[Pierre T. <p.t...@wa...>]

Agreed.
Brandon, you may have a look there: www.codercorner.com\Cloth.htm

I use springs as described by Tom, and I believe it would be just perfect
for a ponytail. Actually the default piece of cloth in the demo could look
like a ponytail once reduced (it's a bit lengthy).

Pierre

----- Original Message -----
From: Tom Forsyth <to...@mu...>
To: <gda...@li...>
Sent: Tuesday, August 29, 2000 11:25 AM
Subject: RE: [Algorithms] Skeletal Animation...


> Use stiff springs between the vertices of the ponytail, and no instant
> propogation down the chain. So each frame, each spring just affects the
ones
> it is attached to. It works just fine for apps like this, where a little
bit
> of deformation is not going to be noticed. Propogating forces/impluses
down
> chains instantly is a real pain, but allowing the springs to do it
> themselves over a few frames makes life much easier. It goes wrong for
some
> apps, but not in this case.
>
> Tom Forsyth - Muckyfoot bloke.
> Whizzing and pasting and pooting through the day.
>
> > -----Original Message-----
> > From: Brandon Moro [mailto:the...@us...]
> > Sent: 29 August 2000 06:59
> > To: gda...@li...
> > Subject: [Algorithms] Skeletal Animation...
> >
> >
> > Hello.
> >
> > I was wondering if anyone had links to some good skeletal animation
> > techniques and perhaps some information about the kinematics involved.
> >
> > For example, if I was a model to have a ponytail which moves
> > realistically.
> > Given gravity and the mass of my character, I should be able
> > to generate the
> > normal force produced by walking (feet hitting the ground).
> >
> > Assuming the ponytail is just a couple bones end-to-end
> > sharing intermediate
> > vertices, the problem I arrive at is the way to correctly
> > propogate a force
> > applied at the origin vertex (ie the one connecting the
> > ponytail to the
> > head) down into the other vertices.
> >
> > Any possible links would be great.  I heard that someone
> > wrote quite a few
> > papers on the physics involved in this, but I can't remember his name
> > exactly.  I know his last name is something like Mirich, but
> > thats not quite
> > it.
> >
> > Thanx!
> > Brandon Moro
> >
> > _______________________________________________
> > GDAlgorithms-list mailing list
> > GDA...@li...
> > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list
> >
> _______________________________________________
> GDAlgorithms-list mailing list
> GDA...@li...
> http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list

[Algorithms] Nearest point on plane for 2D IK

[Jeff L. <je...@di...>]

Since we were talking about skeleton animation, I have a question.

For my IK system, I prefer to use actual 2D joints where appropriate rather then use the general 3D form and limit with DOF restrictions.  I have received some email asking me how to do this with my CCD IK routine so I wanted to write up a paragraph on the little math routine for the magazine.  I think it is pretty obvious to people familiar with vector math, but I have found that many developers don't have the background and need some help.  I will put this in with my continuing series on why dot product is your friend.

I want to sanity check it to make sure this is a good, fast way to do this.  I know that it works but it may not be the best method.

Given a bone object in 3 space, B, and a desired 3D target to attempt to reach, T.  The method is to determine the plane that B is allowed to rotate, then project T into that plane.  Then I solve for the rotation angle.

To project T onto B's free rotational plane:

N = free axis of rotation

V = T - B		// Creates vector from base to target
P = T - N ( N dot V)	// Project V onto axis and subtract that from the target

Now, P is my new target point for the IK routine.  Continue as usual, dot product to get the angle to rotate, ...
I will explain why this works and such but you get the idea.

-Jeff

Re: [Algorithms] Nearest point on plane for 2D IK

[David K. <da...@ik...>]

Hi,

I am looking for an algorithm to compute the intersecting point P between a ray and
a sphere. I know the center C and the radius R of the sphere, the origin O of the ray
and its direction V. Basically I need to find the closest intersection from O.

But that's not all: In addition to this, IF the ray does not intersect or is tangent to the
sphere, I need to know the tangential point with the sphere.

Does anybody know a fast and accurate solution to this problem? maybe a good web
site or some code would greatly help!...

Thanks,

David Kornmann.
--

Re: [Algorithms] Nearest point on plane for 2D IK

[Jeff L. <je...@di...>]

Plug for Dave Eberly's Magic-Software site goes here:

http://www.magic-software.com/MgcIntersection.html

Looks like the code you need is :
Lin3Sphr.h, Lin3Sphr.cpp 

-Jeff

At 09:56 PM 8/29/2000 +0300, you wrote:
>Hi,
>
>I am looking for an algorithm to compute the intersecting point P between a ray and
>a sphere. I know the center C and the radius R of the sphere, the origin O of the ray
>and its direction V. Basically I need to find the closest intersection from O.
>
>But that's not all: In addition to this, IF the ray does not intersect or is tangent to the
>sphere, I need to know the tangential point with the sphere.
>
>Does anybody know a fast and accurate solution to this problem? maybe a good web
>site or some code would greatly help!...
>
>Thanks,
>
>David Kornmann.
>--
>
>_______________________________________________
>GDAlgorithms-list mailing list
>GDA...@li...
>http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list

Re: [Algorithms] Nearest point on plane for 2D IK

[Serge C. <co...@po...>]

Hi,

T'es perdu? C'est toi qui emcombre la mail-list avec des questions de blaireaux. Si tu veux
revenir fair un stage au SEA, tu quand meme le bienvenu.
For info look in Graphics Gems p388: Intersection of a Ray with a sphere.
Serge Couvet

David Kornmann wrote:

> Hi,
>
> I am looking for an algorithm to compute the intersecting point P between a ray and
> a sphere. I know the center C and the radius R of the sphere, the origin O of the ray
> and its direction V. Basically I need to find the closest intersection from O.
>
> But that's not all: In addition to this, IF the ray does not intersect or is tangent to the
> sphere, I need to know the tangential point with the sphere.
>
> Does anybody know a fast and accurate solution to this problem? maybe a good web
> site or some code would greatly help!...
>
> Thanks,
>
> David Kornmann.
> --
>
> _______________________________________________
> GDAlgorithms-list mailing list
> GDA...@li...
> http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list

Re: [Algorithms] Nearest point on plane for 2D IK

[<ro...@do...>]

Jeff Lander  wrote:

>Since we were talking about skeleton animation, I have a question.
>
>For my IK system, I prefer to use actual 2D joints where appropriate =
rather
> then use the general 3D form and limit with DOF restrictions.=20
> I have received some email asking me how to do this with my CCD
> IK routine so I wanted to write up a paragraph on the=20
>little math routine for the magazine. =20
>I think it is pretty obvious to people familiar with vector math,
> but I have found that many developers don't have the background
>and need some help.=20


> I will put this in with my continuing series on why dot product is your=
 friend.
>


>I want to sanity check it to make sure this is a good, fast way to do =
this.=20
> I know that it works but it may not be the best method.
>
>Given a bone object in 3 space, B, and a desired 3D target to attempt to=
 reach, T. =20
>The method is to determine the plane that B is allowed to rotate,=20
>then project T into that plane.  Then I solve for the rotation angle.
>
>To project T onto B's free rotational plane:
>
>N =3D free axis of rotation
>
>V =3D T - B		// Creates vector from base to target

It is not at all clear to me what you mean by B.  Is it a pure vector
(like N) or is it the position vector of a point (like T).  Does it
represent the position of a bone or the relative positions of the two
ends of the bone?=20

This equation only makes sense if B is the position vector of a point.
In that case, it tells where the bone is, but not how it is oriented.
But also, in this case,  "B's free rotational plane" is without
meaning.

>P =3D T - N ( N dot V)	// Project V onto axis and subtract that from the=
 target
>

I think that your criterion for P is that it be perpendicular to N.
This P satisfies that criterion, that is, P is the perpendicular
projection of V on the plane perpendicular to N,  only in the special
case that B is perpendicular to N, which I think is probably not true,
in general, for the systems you want to work with.

The proper vector formula for the perpendicular projection of V on the
plane perpendicular to N is=20

P =3D V - (N dot V)N

and it holds independently of how you construct V.