Re: [www-vrml] OPEN--GL Question

[Leonard Daly <daly@realism.com>]

Juan,

I think I understand your question to be that you want to rotate an
object about another point in space, much like the Earth rotates around
the Sun.

I assume that your object is at the origin (at least in its coordinate
system) and the point in space that you wish for the center of rotation
is Y

You need to transform (move) the object so that the desired center of
rotation is the origin and the object is at -Y.

You then rotate this.

If we call Ty the transform to move Y to the origin, Ra the rotation by
angle a, and O the object, you have

        

Ra (Ty
(O))

I do not know OpenGL, so I cannot help beyond this.

        

Leonard
Daly



At 12:35 PM 3/3/05, Juan Manuel Gonzalez Calleros wrote:
> Hello everybody
>
> I am new in the business of computer graphics and of course 3D. I had a
> problem with transformations in OPENGL. My program, it is supposed that
> should make the rotations ans translations of an object, it works but the
> object rotates just  on its own axis X Y Z, I need that  it
> rotate around the Space. I know and I read that I need to multiply the
> matrix by the matrix inverse but it didn't work or ?I don't know how.
> could you have a view on it and if somebody know what do I need or send
> me a link to any web page with examples or a good explanation on what do
> I need.
> void WireGL::paintGL()
> {
> printf("On est ds paintgl. xTranslat = %f\n",xTranslat);
> printf("Angles GLfloat phiRot, thetaRot, rhoRot : %f, %f,
> %f\n",phiRot,thetaRot,rhoRot);
>
> glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
>
> //trace le repère mondial
> glColor3f((GLfloat)0.7, (GLfloat)0.0, (GLfloat)0.1);
> axis(1,0,0,2);
> axis(0,1,0,2);
> axis(0,0,1,2);
>
> //applique les transformations
> glRotatef(phiRot,1,0,0);
> glRotatef(thetaRot,0,1,0);
> glRotatef(rhoRot,0,0,1);
> glTranslatef(xTranslat,yTranslat,zTranslat);
>
>
> glCallList(object);
>
> //retourne dans le repère initial
> glTranslatef(-xTranslat,-yTranslat,-zTranslat);
> glRotatef(-rhoRot,0,0,1);
> glRotatef(-thetaRot,0,1,0);
> glRotatef(-phiRot,1,0,0);
>
> glFlush();
> }
>
> -- 
> Best Regards
> M. Sc. Juan Manuel González Calleros Ph. D. Student
>
> Université catholique de Louvain (UCL)
> School of Management (IAG)
> Unit of Information Systems (ISYS)
>
> Place des Doyens, 1 (office a.036)
> Louvain-la-Neuve, Belgium P.C. 1348 
> E-mail: gonzalez@isys.ucl.ac.be
> E-mail: jmgonzalez@inaoep.mx  
> E-mail:jumagoca78@hotmail.com web:
> http://www.isys.ucl.ac.be/bchi/members/jgo/index.htm
>
> Phone: +32 10/478349
> Fax: +32 10/478324
>
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+--------
| Leonard Daly <daly@realism.com>
| Internet & Web Consulting http://realism.com/
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| X3D Author and Lecturer
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