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I have noticed that when I use the standard reorient macros, my actors
roll along their axis of movement as they travel in a complete circle.
For example,
1) I develop and algorithm that changes the velocity of an actor so that
it moves in a circle.
2) I then use the calculated velocity to reorient an object such as
reorient (x, new_velocity).
3) I find that as I watch the actor complete a full circle, it has also
rotated about its axis of travel. (In other words, the guy inside the
craft had better be wearing a seat belt!) Or, if I use this macro on
the camera, the ground spins as one travels around in the circle.
Is there a way to make a change or two to the reorient macro so that
this does not occur?
If yall don't understand what I'm talking about, I can post a small
animation with the phenomenon...
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"Greg M. Johnson" wrote:
>
> I have noticed that when I use the standard reorient macros, my actors
> roll along their axis of movement as they travel in a complete circle.
>
> For example,
> 1) I develop and algorithm that changes the velocity of an actor so that
> it moves in a circle.
> 2) I then use the calculated velocity to reorient an object such as
> reorient (x, new_velocity).
> 3) I find that as I watch the actor complete a full circle, it has also
> rotated about its axis of travel. (In other words, the guy inside the
> craft had better be wearing a seat belt!) Or, if I use this macro on
> the camera, the ground spins as one travels around in the circle.
>
> Is there a way to make a change or two to the reorient macro so that
> this does not occur?
> If yall don't understand what I'm talking about, I can post a small
> animation with the phenomenon...
I don't know if I understand it correctly (probably not), but wouldn't it be
possible to do a negative rotation at 0 before anything else?
Remco
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Perhaps translate<Radius*cos(radians(Angle)),0,Radius*sin(radians(Angle))>
would do it.
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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The rub comes in determining the angle. I have vectors that can be pointing in
any which way. I am not making a merry go round, but having particles
(spacecraft, birds) interact with hundreds of other particles via forces which
are in 3d. I want the "orientation" to be correct but with minimum or no
"roll".
A fish or bird in a swarming school might "point" its nose in any direction, but
I'm sure that it maximizes the amount of time its feet are below its body:
minimum roll. The plain ol' reorient macro gives a roll as one reorients around
a circle. My hunch is that I could just change a sign or two in one of the
matrices and be all right.
Nieminen Juha wrote:
> Perhaps translate<Radius*cos(radians(Angle)),0,Radius*sin(radians(Angle))>
> would do it.
>
> --
> main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
> ):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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"Greg M. Johnson" wrote:
>
> The rub comes in determining the angle. I have vectors that can be pointing in
> any which way. I am not making a merry go round, but having particles
> (spacecraft, birds) interact with hundreds of other particles via forces which
> are in 3d. I want the "orientation" to be correct but with minimum or no
> "roll".
>
> A fish or bird in a swarming school might "point" its nose in any direction, but
> I'm sure that it maximizes the amount of time its feet are below its body:
> minimum roll. The plain ol' reorient macro gives a roll as one reorients around
> a circle. My hunch is that I could just change a sign or two in one of the
> matrices and be all right.
>
> Nieminen Juha wrote:
>
Provided you stay in a x-z plane, and provided velocity is normalized,
you can replace your call to reorient by:
matrix <velocity.x, 0, -velocity.y,
0, 1, 0,
velocity.y, 0, velocity.x,
0, 0, 0>
If you don't stay in the x-z plane, there is no real way to do it, you
can still try this if you don't go on too steep slopes:
#local u = vnormalize (<v.x, 0, v.z>);
matrix <v.x, v.y*u.z-v.z*u.y, u.x,
v.y, v.z*u.x-v.x*u.z, u.y,
v.z, v.x*u.y-v.y*u.x, u.z,
0, 0, 0>
(There might be a sign problem in the middle column wich would cause a
"mirror effect", and i might have mixed lines and columns wich would
cause very strange behavior...)
Jerome
--
*******************************
* they'll tell you what can't * mailto:ber### [at] iname com
* be done and why... * http://www.enst.fr/~jberger
* Then do it. *
*******************************
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In article <3803567E.4817F34B@xs4all.nl> , Remco de Korte
<rem### [at] xs4allnl> wrote:
> I don't know if I understand it correctly (probably not), but wouldn't it be
> possible to do a negative rotation at 0 before anything else?
I understand his question the same way, it should work. Of course you need
to make sure you have the correct "center" to rotate in place if the object
is a bit more complex.
Thorsten
____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde
Visit POV-Ray on the web: http://mac.povray.org
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Greg M. Johnson wrote:
>
> The rub comes in determining the angle. I have vectors that can be
> pointing in any which way. I am not making a merry go round, but
> having particles (spacecraft, birds) interact with hundreds of other
> particles via forces which are in 3d. I want the "orientation" to be
> correct but with minimum or no "roll".
>
> A fish or bird in a swarming school might "point" its nose in any
> direction, but I'm sure that it maximizes the amount of time its feet
> are below its body: minimum roll. The plain ol' reorient macro gives
> a roll as one reorients around a circle. My hunch is that I could
> just change a sign or two in one of the
> matrices and be all right.
Now that you have stated your problem with more precision, I can help.
As a rule, I design objects so that x is right, y is up, and z is
forward, and what I consider to be the "center" is at the origin.
If I want to have it face a given direction, with its top as close to
up as possible, and located at a given place, I do the following:
// sample code
// assumes that Direction= the direction the object needs to face
// Sky = the direction that's up in your world
// Location = where it needs to go
#local vZ=vnormalize(Direction);
#local vX=vnormalize(vcross(Sky,vZ));
#local vY=vnormalize(vcross(vZ,vX));
object { MyObject Matrix(vX,vY,vZ,Location) }
// end of sample code
Hope this helps,
John
--
ICQ: 46085459
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"Greg M. Johnson" wrote:
>
> I have noticed that when I use the standard reorient macros, my actors
> roll along their axis of movement as they travel in a complete circle.
>
> For example,
> 1) I develop and algorithm that changes the velocity of an actor so that
> it moves in a circle.
> 2) I then use the calculated velocity to reorient an object such as
> reorient (x, new_velocity).
> 3) I find that as I watch the actor complete a full circle, it has also
> rotated about its axis of travel. (In other words, the guy inside the
> craft had better be wearing a seat belt!) Or, if I use this macro on
> the camera, the ground spins as one travels around in the circle.
>
> Is there a way to make a change or two to the reorient macro so that
> this does not occur?
> If yall don't understand what I'm talking about, I can post a small
> animation with the phenomenon...
Came across a new calculator today you might be interested in:
Spin Doctor - This is a calculator that operates on 3D vectors and
rotations, making it an invaluable tool for 3D content and application
developers. A wide variety of operations are provided, from simple
vector addition, to scaling, rotation, and calculation of angles
and lengths.
http://www.vapourtech.com/news.html
--
Ken Tyler - 1100+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/
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Wait. You've suddenly put in a matrix only defined by "Matrix." Is this a
capital M??
John VanSickle wrote:
> Greg M. Johnson wrote:
> >
> > The rub comes in determining the angle. I have vectors that can be
> > pointing in any which way. I am not making a merry go round, but
> > having particles (spacecraft, birds) interact with hundreds of other
> > particles via forces which are in 3d. I want the "orientation" to be
> > correct but with minimum or no "roll".
> >
> > A fish or bird in a swarming school might "point" its nose in any
> > direction, but I'm sure that it maximizes the amount of time its feet
> > are below its body: minimum roll. The plain ol' reorient macro gives
> > a roll as one reorients around a circle. My hunch is that I could
> > just change a sign or two in one of the
> > matrices and be all right.
>
> Now that you have stated your problem with more precision, I can help.
>
> As a rule, I design objects so that x is right, y is up, and z is
> forward, and what I consider to be the "center" is at the origin.
>
> If I want to have it face a given direction, with its top as close to
> up as possible, and located at a given place, I do the following:
>
> // sample code
> // assumes that Direction= the direction the object needs to face
> // Sky = the direction that's up in your world
> // Location = where it needs to go
>
> #local vZ=vnormalize(Direction);
> #local vX=vnormalize(vcross(Sky,vZ));
> #local vY=vnormalize(vcross(vZ,vX));
>
> object { MyObject Matrix(vX,vY,vZ,Location) }
>
> // end of sample code
>
> Hope this helps,
> John
> --
> ICQ: 46085459
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Greg M. Johnson wrote:
>
> John VanSickle wrote:
>
> > Greg M. Johnson wrote:
> > >
> > > The rub comes in determining the angle. I have vectors that can be
> > > pointing in any which way. I am not making a merry go round, but
> > > having particles (spacecraft, birds) interact with hundreds of other
> > > particles via forces which are in 3d. I want the "orientation" to be
> > > correct but with minimum or no "roll".
> > >
> > > A fish or bird in a swarming school might "point" its nose in any
> > > direction, but I'm sure that it maximizes the amount of time its feet
> > > are below its body: minimum roll. The plain ol' reorient macro gives
> > > a roll as one reorients around a circle. My hunch is that I could
> > > just change a sign or two in one of the
> > > matrices and be all right.
> >
> > Now that you have stated your problem with more precision, I can help.
> >
> > As a rule, I design objects so that x is right, y is up, and z is
> > forward, and what I consider to be the "center" is at the origin.
> >
> > If I want to have it face a given direction, with its top as close to
> > up as possible, and located at a given place, I do the following:
> >
> > // sample code
> > // assumes that Direction= the direction the object needs to face
> > // Sky = the direction that's up in your world
> > // Location = where it needs to go
> >
> > #local vZ=vnormalize(Direction);
> > #local vX=vnormalize(vcross(Sky,vZ));
> > #local vY=vnormalize(vcross(vZ,vX));
> >
> > object { MyObject Matrix(vX,vY,vZ,Location) }
> >
> > // end of sample code
>
> Wait. You've suddenly put in a matrix only defined by "Matrix." Is
> this a capital M??
I assumed you were using my macros file (which contains the Reorient
macro); it also has a Matrix() macro, which makes it easier to build
a matrix transform out of a bunch of vectors.
Note that there are round brackets in the statment instead of angle
brackets; it's a macro call.
--
ICQ: 46085459
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