Quaternion Camera

Hello there: this is the code I use to rotate for my Quaternion Camera. It is done in JOGL (Java).

  public void rotate(double speed, Vector3 vAxis) {
    Quaternion qRot = new Quaternion();
    Quaternion qNewDir = new Quaternion(vView.sub(vPosition));
    Quaternion qNewRot = new Quaternion();
    qRot = qRot.buildFromAxisAngle(speed, vAxis);
    qNewRot = qRot.mult(qNewDir).mult(qRot.conjugate());
    vView = vPosition.add(qNewRot.v);
  }

  public void orbit(Vector3 vCenter, double speed, Vector3 vAxis) {
    Quaternion qRot = new Quaternion();
    Quaternion qNewPos = new Quaternion();
    Vector3 vTmp = vPosition.sub(vCenter);
    Quaternion qPos = new Quaternion(vTmp);
    qRot = qRot.buildFromAxisAngle(speed, vAxis);
    qNewPos = qRot.mult(qPos).mult(qRot.inverse());
    Vector3 v = qNewPos.v;
    vPosition = vView.add(v);
  }

It works fairly well, except in orbiting around a point on the X Axis. I still haven''t been able to find a solution.
The problem is that if I''m looking North (for example), it rotates OK making a sort of circular path around the object (passing above and then beneath). If I move myself to the right, and try to orbit on the X-Axys, it still makes a circular path.. The problem is that these circular path are parallel.

Let me explain better: if I''m looking at an object from south to north it rotates in a circular path around the object. If I position myself on the right side so that I''m looking at the object from the east to the west.. it makes a circular path parallel to the first. In theory from east->west it should make a circular path that intersects the previous one, right? The viewing directiong remains centered anyway (so that when I''m orbiting it still look at the same point).

I''m sure it''s an easy thing to fix.. But I really don''t know.. any help would be really appreciated.

Thanks for your code.
Now I really apreciate C++''s operator overloading

Anyway I''ll also check into your orbit code for you.


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hehe, one day i''ll count the operations needed for a quat and a matrix camera, just to see if there is any reason for one at all. i wouldnt be surprised if all this back and forth and using glulookat etc. is just more work and less intuitive.

question is: do you want to rotate around _global_ or _local_ x,y,z axes? also, be careful to make sure those tutorials arent some of those "lets use quaternions and still use euler angles and wonder why it still cant work, because flawed math is flawed math, no matter what kind of space youre doing it in". dressing up euler angles in quaterions instead of matrices to apply rotations will simply not make any difference.

btw. i just learned to appreciate the ability to overload implicit typecasting. passing a vector class to opengl functions like it was a float* (ie. glVertex3fv(V)) instead of passing x,y,z seperatly or using ugly ways (ie glVertexfv(V.x) or glVertexfv((float*)&V)) and not to mention the even uglier c++ typecasts *fg*) can make code so nice and clean. i just wish it had options to add new operators (never find a good for cross product and using & can be confusing for someone to read *fg*). but: better start using a lot of brackets to make sure it wont screw up the order (compiler cant know if your own operator x is binding stronger or weaker than operator y)

If you can show me how to perform all those above mentioned rotations (around the camera''s axis and/or orbitally) without Quaternions, then I''ll drop that and use something simpler and faster.

I can easily code a camera thats like a first person shooter cam where you can look up/down , etc. But I want a camera that can do almost anything I want to.

So until then I''m using Quaternions.


// Last Attacker \\---=( LA )=---// LA Extreme \\

ICQ Number : 120585863

E-mail: laextr@icqmail.com

well, you want to rotate either around your objects right/up/front (which is exactly what glrotate does, the only "trick" is to store this matrix and only update it with the new rotations each frames) or around the global x,y,z axes, which means either letting the matrices switch place (easy) or rotating around the axis you get by inverting the matrix (extra work).

for opengl to rotate you just do this (do the matrix math yourself if you do it a lot each frame as reading back the matrix from the card might be a little slow if you do it hundreds of times):
void CameraGL::rotate(float deg, float x, float y, float z, bool global) {
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadMatrixf(Transform);

if (global) glRotatef(deg,
x*Transform[0] + y*Transform[1] + z*Transform[2],
x*Transform[4] + y*Transform[5] + z*Transform[6],
x*Transform[8] + y*Transform[9] + z*Transform[10]);
else glRotatef(deg, x,y,z);
glGetFloatv(GL_MODELVIEW_MATRIX, Transform);
glPopMatrix();
}

for your quat camera you probably store view/up and position vectors, which is just what you find in the matrix (plus a "right" vector that can be handy to strafe). if you dont like storing 16 floats you can get away with 9 (view,up,position) but have to get the right vector via cross product and add w components, which is btw. just what glulookat does.

Thanks Trienco!

The only thing I don''t like about gluLookAt is that you cannot rotate above or below the 90'' up or down angles without invertically jumping to another direction.

I guess you have to rotate the Up Vector but I don''t know how or if it will help.

Thanks

// Last Attacker \\---=( LA )=---// LA Extreme \\

ICQ Number : 120585863

E-mail: laextr@icqmail.com

hm.. what i dont like about glulookat is that with a matrix camera you would basically first convert your perfect vectors into the form glulookat is expecting, just so it can turn them back into what you already had (with two completely unnecessary cross products etc.). and without glulookat i even removed the last glu function.

but one way or another, you need at least TWO vectors and trying to get away with just the view vector will bite you sooner or later ,-)

Anyway, concerning the quaternions, what would I need to change in order to fix the Rotation issue I described above?