[x3d-public] [h-anim] Basic Animataion data

[Joe D Williams]

Thanks, Roy
Repository at:

http://www.graphicsgems.org/


----- Original Message ----- 
From: "Roy Walmsley" <roy.walmsley at ntlworld.com>
To: "'Joe D Williams'" <joedwil at earthlink.net>
Cc: "'X3D Graphics public mailing list'" <x3d-public at web3d.org>; 
"'Humanoid Animation (H-Anim) Working Group'" <h-anim at web3d.org>
Sent: Friday, November 11, 2016 3:41 AM
Subject: RE: [h-anim] Basic Animataion data


> Hi Joe,
>
>
>
> Great summary and references. However, one of the references you 
> listed is
> incorrect. You wrote:
>
>
>
> Schlag, 1994] John Schlag. Using geometric constructions to 
> interpolate
> orientation with quaternions. Graphics Gems IV, pages 230-236, 1994.
>
>
>
> In fact, the article by John Schlag you are referring to is:
>
> John Schlag. "Using Geometric Constructions to Interpolate 
> Orientation with
> Quaternions". In Graphics Gems II, Academic Press, 1991, pp. 
> 377-380.
>
>
>
> Consulting Graphic Gems IV, pages 230-236, there is an article 
> "Fiber Bundle
> Twist Reduction", by Ken Shoemake at that location.
>
>
>
> Regards,
>
>
>
> Roy
>
>
>
>
>
> -----Original Message-----
> From: h-anim [mailto:h-anim-bounces at web3d.org] On Behalf Of Joe D 
> Williams
> Sent: 11 November 2016 01:30
> To: X3D Graphics public mailing list <x3d-public at web3d.org>; 
> Humanoid
> Animation (H-Anim) Working Group <h-anim at web3d.org>
> Subject: [h-anim] Basic Animataion data
>
>
>
>
>
> glossary:
>
> Transform rotation value
>
>
>
> * Euler angle - typical mocap-derived
>
>  animation data = x,y,z
>
>     (x,y,z = degrees)
>
> Mocap data represents:
>
>  * Bone or Segment orientation
>
>      or
>
> * parent Joint rotation
>
> Either interpretation represents
>
> same animation
>
>
>
>
>
> * matrix = axis-angle = x,y,z,a
>
>     x,y,z = radians,
>
>     a = scale factor
>
>
>
> X3D Default
>
> Easy to hand-edit
>
>
>
>
>
> * Unit quaternion = w,x,y,z
>
>
>
>      w+x+y+z = 1 = unit q
>
>
>
> Most common authoring tool internal and transport form Easy to add 
> unit
> quats for realtime interpolated animation Can use hand-edit as 
> w=scale
> factor and x,y,z are axes  if careful to maintain uq
>
>
>
>
>
> * Standards-Track Lossless conversion between forms.
>
>
>
> First, please notice that this Animation data is aimed at describing
> keyframe animation of a set of hierarchal "Joint" nodes.
>
>
>
> Animation data is provided as arrays of:
>
> keyframe root position data,
>
> keyframe rotation data for each joint,
>
> number of keyframes,
>
> target key time frame interval
>
>
>
> The data is used by defining the root position and each joint 
> rotation at
> each key time. For film and video there is often no need for a list 
> of key
> times indexed to each keyvalue because the frame interval is fixed.
>
>
>
> Notice that typically, there is no consideration for non-monotonic 
> key
> times, although it is highly unlikely to encounter an X3D browser 
> that does
> not allow non-monotonic key times. Why, allow non-monotonic key 
> times?
> Because it is usually convenient for the author to consider each 
> joint
> individually and individually define the interval between associated
> keyvalue data points, and to minimize the actual number of key times 
> and
> thus keyvalues.
>
>
>
> At this time, in order for an X3D HAnim to use most types of mocap 
> data it
> would only be required:
>
>
>
> 1. Connect the joint names
>
> 2. Convert the input data form to axis-angle, 3, Construct the 
> interpolators
> and timers for each joint
>
>
>
> This style of animation depends mainly or solely on application of
> individual rotations to individual joints in a set of hierarchal 
> 'Joint'
> nodes at each key time to produce the keyframe. Current best 
> practice for
> this style of animation uses unit quaternions due to efficiency. 
> Even though
> the most throughly complete technical solution remains axis-angle 
> matrix
> transformations, the unit quats are easy to transport and used 
> natively in
> many animation creation and development tools.
>
>
>
> So, the choice of gltf to only transport quaternions should cause 
> X3D and
> HAnim to address the idea of built-in quaternion support. As is 
> well-shown,
> the maths of these three forms are well defined and conversion 
> interactions
> are well understood.
>
>
>
> * At this time we are creating prototype support for BVH x,y,z ffps 
> import,
> it seems only reasonable to encourage import of both Euler angle and 
> unit
> quaternion forms.
>
>
>
> Background
>
>
>
> Quaternions, Interpolation and Animation Erik B. Dam Martin Koch 
> Martin
> Lillholm  <mailto:erikdam at diku.dk> erikdam at diku.dk 
> <mailto:myth at diku.dk>
> myth at diku.dk  <mailto:grumse at diku.dk> grumse at diku.dk Technical 
> Report
> DIKU-TR-98/5 Department of Computer Science University of Copenhagen
> Universitetsparken 1
>
> DK-2100 Kbh Denmark
>
> July 17, 1998
>
>
>
> Interesting Material.
>
> I have a copy of a pdf.
>
>
>
> Appendix A - Conventions
>
>
>
> Coordinate system
>
> (slightly reworded by me to aim at X3D and HAnim)
>
>
>
> X3D and HAnim use a right-handed coordinate system. In computer 
> graphics
> some use a left-handed coordinate system. This allows the z-axis to 
> point
> "into" the screen which seems natural for some styles of authoring.
> However, since X3D primarily uses coordinates for animations driven 
> by
> mathematical derivations and for Humanoid animations, VRML and X3D 
> have
> chosen to use the mathematical standard, the right-handed coordinate 
> system.
>
>
>
> Rotation.
>
>
>
> This means that the default Humanoid pose gaze is facing +z.
>
> The +z axis for the character points "out" of the screen,
>
> +y is up,
>
> and +x is towards the character's left, viewer's right.
>
> The default X3D viewpoint is oriented to look toward -z.
>
>
>
> The direction of positive, or increasing rotation about an axis is 
> obtained
> by the right-hand rule:
>
>
>
> Hold the axis with right hand and the thumb pointing in the positive
> direction of the axis.
>
>
>
> Adding positive rotation will rotate in the direction of the 
> fingers.
>
>
>
> It just happens that HAnim Joint rotations can be vizualized in 
> terms of
> x=pitch, y=yaw, and z=roll.
>
>
>
> Again, hold the Joint, as if you were holding the appropriate axis 
> with
> right hand and the thumb pointing in the positive direction of the 
> axis.
>
>
>
> A positive rotation will rotate the Joint and move child hierarchies 
> in the
> direction your fingers are wrapped around the axis.
>
>
>
> For instance, consider a roll (positive z-axis) animation of a 
> Joint, as
> would be appropriate for HAnim right hand fingers from the default 
> pose..
> The fingers are pointing down and thumb pointing toward +z. To move 
> the
> fingers as if grasping the z-axis, rotate the finger joint(s) to 
> increase
> their z-axis rotation.
>
>
>
> Amazingly enough, this results in the character's right hand 
> wrapping around
> the z-axis with the thumb pointed +z, and illustrates the right-hand 
> rule
> perfectly.
>
>
>
> Incidentally, this means that to get proper orientation for a gaze 
> from the
> 'standard' eyeball location, then you can yaw the viewpoint
>
> +pi radians.
>
>
>
> Transport Animations
>
>
>
> In order to transport animations between 'standard' H-Anim 
> characters,
>
> to accomplish the HAnim 'standard' initial pose prior to animation 
> the
>
> Joint is defined to be at X3D default orientation, +z is out of the
>
> screen, +y is up, and +x is towards the character's left.
>
>
>
> The default initial value for all Joints:
>
> X3D axis-angle (matrix) form is 0 0 1 0
>
> and for unit quatenions is 1 0 0 0
>
>
>
> An illustration:
>
> [standard X3D default transformations
>
> X3D coordinate axes]
>
> z (+ out toward viewer)
>
> y (+ up)
>
> x (+ character's left)
>
> Rotation about z brings x into y
>
> Rotation about y brings z into x
>
> Rotation about x brings y into z
>
>
>
>
>
> Schlag, 1994] John Schlag.
>
> Using geometric constructions to
>
> interpolate orientation with quaternions.
>
> Graphics Gems IV, pages 230-236, 1994.
>
>
>
> [Shoemake & Du
>
> , 1994] Ken Shoemake & Tom Du
>
> . Matrix animation and
>
> polar decomposition.
>
> <ftp://ftp.cis.upenn.edu/pub/graphics/shoemake/polar-decomp.ps.Z>
> ftp://ftp.cis.upenn.edu/pub/graphics/shoemake/polar-decomp.ps.Z, 
> 1994.
>
>
>
> Shoemake, 1994b] Ken Shoemake. Quaternions.
>
> <ftp://ftp.cis.upenn.edu/pub/graphics/->
> ftp://ftp.cis.upenn.edu/pub/graphics/-
>
> shoemake/quatut.ps.Z, 1994.
>
>
>
> Thanks and Best,
>
> Joe
>
>
>
>
>
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