"Chris B" <nom### [at] nomailcom> wrote:
> "melo" <mel### [at] coxnet> wrote in message
> news:web.47c7cf38dddebe08587ef5e20@news.povray.org...
> >I got myself into a few more exception errors.  Chris.  Your
> >recommendations on
> > how to trace such an error is of utmost value, I wonder if it could go
> > into a
> > How To library of information for those of us who tend to get themselves
> > into
> > trouble quite often.
> >
> > Well, s/he is walking but s/he is not going anywhere.
> >
> > By rereading your posting it sounded like you used lots of neat 3D
> > geometry to
> > figure out how to map 3D rotation vectors of joints into joints
> > coordinates in
> > 3D.
>
> I did spend a lot of time on developing the 3D geometry and joint rotation
> stuff to my own satisfaction.  I wanted a system where poses could be
> readily hand coded, so I wanted flexibility over how to specify each set of
> joint rotations.
>
> > Given each segment spans two joints and the tree structure of Skeletal
> > being then you have all you need to construct it and render it.
>
> I wouldn't quite agree with this statement. Some body parts are only
> connected to one joint. Others are connected to many, for example the palm
> of each hand has joints with the wrist and with the base of each finger.
>
> > I have taken a much simpler approach, and relied on POV-RAY for forward
> > kinematics.  Given a pose, i.e joint rotation vectors involved in that
> > pose,
> > and
> > a hierarchically unioned CSG, placing
> >
> >      Rotate_Around_Trans( AVAR[R_Hip_Ind], JOC_R_Hip )
> >
> > kind of rotations throughout object creation, did the trick.  POV-RAY very
> > nicely determines where to place segments as a result of a set of
> > rotations
> > burried within CSG tree.
> >
> > Once I construct my Humanoid in his/her current Pose, I apply the same
> > transformation to her/him as I render him.  So s/he gets nicely scaled and
> > positioned in the display window.
> >
> > Now that all poses and transition are good enough, I thought I could make
> > him/her move in the direction s/he takes his steps.  I calculated his step
> > size
> > and tired to translate her/him by clock, so by the time s/he moves to his
> > cross-over pose s/he would be completely moved over his one standing leg
> > which
> > was his forward leg.
> >
> > I hoped
> >
> >   #if ( !VZero( Forward_Foot_Coord ) )
> >      object {
> >         TransformedHumanoid
> >
> >         //Align left side of object to be coplanar with Forward_Foot_Coord
> >         Align_Trans( TransformedHumanoid, -x, Forward_Foot_Coord )
> >
> >         //Align bottom of object to be coplanar with Forward_Foot_Coord
> >         Align_Trans( TransformedHumanoid, -y, Forward_Foot_Coord )
> >      }
> >
> > Here Forward_Foot_Coord is the coordinates of whichever foot had just
> > strode
> > forward. As Humanoid gathers his back leg into cross-over position his
> > center
> > of gravity gets shifted over the heal of his forward foot.
> >
> > Align_Trans would be a very crude 1st approximation, what would you
> > recommend
> > that I do?  So he moves.   For later, I like him to follow footsteps laid
> > out.
>
> In mine I had an array to store all of the joint locations and a macro that
> repeatedly scanned back and forth through the array calculating locations
> that hadn't yet been calculated, where one of the adjoining ones had. To
> start the process of resolving the pose I therefore just had to fix the
> position of a single body part (using my ppFixBodyPart macro) then run the
> location resolution macro to resolve the remaining positions. It only had to
> scan back and forth a couple of times to resolve all unresolved positions.
>
> For my walking animation I fixed the Right Foot for the first half and the
> Left Foot for the second half. Because the array ends up holding the
> position of both feet, I was able to simply display the position of the Left
> Foot at the end of the first half of the animation cycle and plug the result
> into the key frames for the second half of the animation.
>
> I would think that you could achieve something similar with your accumulated
> tranformations using Align_Trans. You could use #debug to output the
> position where the moving foot comes flat on the ground. Presumably you
> record the cumulative transformations from a single fixed body part in an
> array. If so you can get the tranformation from any body part to any other
> body part by using 'inverse' to transform a point or an orientation vector
> relative to the fixed body part, then use the transform for the second body
> part to derive it's position/orientation.
>
>  > For later, I like him to follow footsteps laid out.
>
> I've thought about that in the past, but concluded it might be better and
> easier to define a walk path as a spline rather than trying to aim for very
> specific foot locations (though I never got around to trying either). I
> figured you could have a parameter to approximately control stridelength and
> then work out from the change of direction of the spline how much the body
> would need to turn to the left or right during a particular step. Scaling
> rotations to get the person turning and striding by roughly those amounts
> should be fairly trivial compared with working out specific foot-fall
> locations.
>
> I also had thoughts on automating the transition to an alternative
> animation, such as transitioning from walking across a floor to climbing up
> some stairs. I figured that by defining a spline through space I could drop
> a line using the 'trace' function to the surface and work out whether the
> person needed to step up/step down or walk on the level automatically. Some
> of my initial workings on this were built into the crowd control functions
> where I positioned people on a surface, and used the 'trace' function to
> make sure they weren't too close to the edge or on too steep a gradient.
>
> Laying out specific footsteps that the character's feet must hit starts to
> bring you into the difficult area of how to define more than one fixed body
> part and how to calculate movement so that the rest of the body moves
> without moving those fixed points.  It then gets tricky to make sure that
> the body parts still link up correctly.
>
> Regards,
> Chris B.

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