Y rotation from rotation matrix

问题

Here are my axes. i dont know what to call it. (is it ZXY?) (this is what camera sees)

i want to know plane rotation around Y axis. Currently it is 0 degree around Y.

here is what i do,

Matrix33 orientmatrix = body->getGlobalOrientation();
return Degree(-asin(orientmatrix[2][0]));

this returns incorrect angles, in counterclockwise: 0..45..90..45..0..-45..-90..-45..0

it should be: 0...45..90..135..180..-45..-90..-135..0

what am i doing wrong?

thank you.

(this is OGRE, code is C++)

回答1:

What you are doing wrong is that you are using asin. It returns a value between -pi/2 to +pi/2, or -90 degrees to +90 degrees.

If you want a value that spans 360 degrees you need to be using atan2. Assuming your orientation truly is a rotation about y, you could use

Degree(atan2(orientmatrix[0][2], orientmatrix[0][0]))

来源：https://stackoverflow.com/questions/10971558/y-rotation-from-rotation-matrix