# 3d rotation.

I need to rotate object around its geometric center (coordinates of which are known: cx,cy and cz). Also, I need to rotate it around axes, which are themselves rotated, since it's a freespace sim. I'm trying to use quaternions, but so far rotation only seems to work in simple cases (i.e. while axes are unrotated), so I need help. I'm using OpenGL and following code:

[code]
//New, rotated axises:
int asize = 1;

double ox_newx = asize*cos(yaw)*cos(roll);
double ox_newy = asize*cos(roll)*sin(yaw);
double ox_newz = -asize*sin(roll);

double oy_newx = -asize*sin(yaw)*cos(pitch);
double oy_newy = asize*cos(yaw)*cos(pitch);;
double oy_newz = asize*sin(pitch);

double oz_newx = -asize*cos(pitch)*sin(roll);
double oz_newy = -asize*sin(pitch);
double oz_newz = asize*cos(pitch)*cos(roll);

//Rotation:
struct QUAT q1 = make_quat(ox_newx,ox_newy,ox_newz,pitch);
struct QUAT q2 = make_quat(oy_newx,oy_newy,oy_newz,roll);
struct QUAT q3 = make_quat(oz_newx,oz_newy,oz_newz,yaw);

struct QUAT res_quat = mul_3_quat(q1,q2,q3);

GLdouble m[4][4];
quat_to_matrix(res_quat,m);
glMultMatrixd(*m);
glTranslatef(-cx, -cy, -cz);
//Rendering:
glCallList(node->user.d);
[/code]

• Hi,

When you do glMultMatrix* and glTranslate encapsulate them into glPushMatrix and glPopMatrix so unnecessary transformation don't happen. Plus previous matrix state is saved as well. Probably this is what is causing the problem

: I need to rotate object around its geometric center (coordinates of which are known: cx,cy and cz). Also, I need to rotate it around axes, which are themselves rotated, since it's a freespace sim. I'm trying to use quaternions, but so far rotation only seems to work in simple cases (i.e. while axes are unrotated), so I need help. I'm using OpenGL and following code:
:
: [code]
: //New, rotated axises:
: int asize = 1;
:
: double ox_newx = asize*cos(yaw)*cos(roll);
: double ox_newy = asize*cos(roll)*sin(yaw);
: double ox_newz = -asize*sin(roll);
:
: double oy_newx = -asize*sin(yaw)*cos(pitch);
: double oy_newy = asize*cos(yaw)*cos(pitch);;
: double oy_newz = asize*sin(pitch);
:
: double oz_newx = -asize*cos(pitch)*sin(roll);
: double oz_newy = -asize*sin(pitch);
: double oz_newz = asize*cos(pitch)*cos(roll);
:
: //Rotation:
: struct QUAT q1 = make_quat(ox_newx,ox_newy,ox_newz,pitch);
: struct QUAT q2 = make_quat(oy_newx,oy_newy,oy_newz,roll);
: struct QUAT q3 = make_quat(oz_newx,oz_newy,oz_newz,yaw);
:
: struct QUAT res_quat = mul_3_quat(q1,q2,q3);
:
: GLdouble m[4][4];
: quat_to_matrix(res_quat,m);
: glMultMatrixd(*m);
: glTranslatef(-cx, -cy, -cz);
: //Rendering:
: glCallList(node->user.d);
: [/code]
:
:
:

• : Hi,
:
: When you do glMultMatrix* and glTranslate encapsulate them into glPushMatrix and glPopMatrix so unnecessary transformation don't happen. Plus previous matrix state is saved as well. Probably this is what is causing the problem
:
Unfortunately, no, writing this
[code]
GLdouble m[4][4];
quat_to_matrix(res_quat,m);
glPushMatrix();
glMultMatrixd(*m);
glTranslatef(-cx, -cy, -cz);
//Rendering:
glCallList(node->user.d);
glPopMatrix();
[/code]
won't help. I guess I'm wrong about either calculating rotated axises, or I've made an error in quaternion math. Hmmm... What's the correct order to multiply three quaternions that specify three rotations?
• I would suggest you check the rotation one at a time to check if its going wrong with the math or the order or multiplication is wrong. Although order of multiplication going wrong can be high its probably a low possiblity that you wouldn't see the problem immediately on a render.

: : Hi,
: :
: : When you do glMultMatrix* and glTranslate encapsulate them into glPushMatrix and glPopMatrix so unnecessary transformation don't happen. Plus previous matrix state is saved as well. Probably this is what is causing the problem
: :
: Unfortunately, no, writing this
: [code]
: GLdouble m[4][4];
: quat_to_matrix(res_quat,m);
: glPushMatrix();
: glMultMatrixd(*m);
: glTranslatef(-cx, -cy, -cz);
: //Rendering:
: glCallList(node->user.d);
: glPopMatrix();
: [/code]
: won't help. I guess I'm wrong about either calculating rotated axises, or I've made an error in quaternion math. Hmmm... What's the correct order to multiply three quaternions that specify three rotations?
:

• : I would suggest you check the rotation one at a time to check if its
: going wrong with the math or the order or multiplication is wrong.
: Although order of multiplication going wrong can be high its probably
: a low possiblity that you wouldn't see the problem immediately on a
: render.

Thanx, but I've spotted the problem already. I was storing wrong parameters. Now it works this way: I store last rotation matrix used and rotated axes. When object is rotated more, I first apply stored rotation matrix, then calculate and apple additional rotation around stored axes, then store old rotation matrix multiplied by new rotation matrix and new axes. Uh, probably my english is not good enough to describe this the right way