Extracting rotation from matrix

Blitz3D Forums/Blitz3D Programming/Extracting rotation from matrix

John J. (Posted 2006) [#1]

I am making a physics engine in C++ for Blitz3D for my latest project, and internal rotations are represented by 4x4 matrices. What I need to know is how to extract a rotation from the matrix which can be used by Blitz3D. I know how to extract an XYZ rotation from a matrix, but I don't know how to extract a ZXY rotation (which I think Blitz3D uses).

Tom (Posted 2006) [#2]

From Sweenies Tokamak Wrapper: neV3 Mat3ToEulerZXY(neM3 Matrix) { float m_afEntry[9]; float rfXAngle; float rfYAngle; float rfZAngle; neV3 Result; m_afEntry[0] = Matrix.M[0].v[0]; m_afEntry[1] = Matrix.M[0].v[1]; m_afEntry[2] = Matrix.M[0].v[2]; m_afEntry[3] = Matrix.M[1].v[0]; m_afEntry[4] = Matrix.M[1].v[1]; m_afEntry[5] = Matrix.M[1].v[2]; m_afEntry[6] = Matrix.M[2].v[0]; m_afEntry[7] = Matrix.M[2].v[1]; m_afEntry[8] = Matrix.M[2].v[2]; if ( m_afEntry[7] < 1.0f ) { if ( m_afEntry[7] > -1.0f ) { rfZAngle = (float)atan2(-m_afEntry[1],m_afEntry[4]); rfXAngle = (float)asin((double)m_afEntry[7]); rfYAngle = (float)atan2(-m_afEntry[6],m_afEntry[8]); Result.v[0] = rfXAngle; Result.v[1] = rfYAngle; Result.v[2] = rfZAngle; return Result; } else { // WARNING. Not unique. ZA - YA = -atan(r02,r00) rfZAngle = (float)-atan2(m_afEntry[2],m_afEntry[0]); rfXAngle = -1.570796f; rfYAngle = 0.0f; Result.v[0] = rfXAngle; Result.v[1] = rfYAngle; Result.v[2] = rfZAngle; return Result; } } else { // WARNING. Not unique. ZA + YA = atan2(r02,r00) rfZAngle = (float)atan2(m_afEntry[2],m_afEntry[0]); rfXAngle = 1.570796f; rfYAngle = 0.0f; Result.v[0] = rfXAngle; Result.v[1] = rfYAngle; Result.v[2] = rfZAngle; return Result; } } Check out Marks native code too: http://www.blitzbasic.com/Community/posts.php?topic=42657

John J. (Posted 2006) [#3]

Thanks, that works fine.