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Gimbal Lock

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Alexey Vanzhula
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Hi. Vex can transform in global space very well with ‘scale’ and ‘rotate’ functions. Even if scale has something like {1, 0, 1} values. But I can`t extract rotations as eulers from result matrix be cause gimbal lock/ I need euler angles to use it in Edit SOP. So how to prevent fail rotation extraction when scale is 1, 0, 1?
Edited by Alexey Vanzhula - 2016年11月27日 11:06:01
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Alexey Vanzhula
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538 posts
Joined: 12月 2006
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vector m, M, center, pt_pos;
matrix mat, rmat, smat;
string pts_str = chs("group");
// GET WORLD TRANSFORM MATRIX
mat = getspace("space:current", "space:world");
// GET POINTS ('GROUP' PARM) CENTROID
getpointbbox(0, pts_str, m, M);
center = ((m+M) / 2) * mat;
// MAKE TRANSFORM MATRIX. SCALE BY 'Y' AND ROTATE BY 'X'
rmat = ident();
scale(rmat, set(1, ch("s"), 1));
rotate(rmat, radians(ch("r")), {1, 0, 0});
// GET POINTS ARRAY FROM 'GROUP' PARM
int pts[] = expandpointgroup(0, pts_str);
// TRANSFORM POINTS
foreach(int pt; pts)
{
    pt_pos = point(0, "P", pt);
    pt_pos *= mat;    
    pt_pos -= center;
    pt_pos *= rmat;
    pt_pos += center;
    pt_pos *= invert(mat);
    setpointattrib(0, "P", pt, pt_pos);
}

How to translate this vex functionality (when scale={1,0,1}) to xform sop values: tx, ty, tz, rx, ry, rz, sx, sy, sz, px, py, pz, shear1, shear2, shear3?
Edited by Alexey Vanzhula - 2016年11月28日 12:53:40
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