x''=z*sin(yaw)+x*cos(yaw) y''=y z''=z*cos(yaw)-x*sin(yaw) Matrix to rotate around x axis: [ cos(a) -sin(a) 0 0 ] [ sin(a) cos(a) 0 0 ] [ 0 0 1 0 ] [ 0 0 0 1 ] I don''t understand why the 0 0 1 is in the Z vector. Or is that the Z vector? Nevertheless, it doesn''t fit the Y vector anyway I look at it. What''s going on? subnet_rx

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Your matrix performs a rotation around the Z axis through angle a. Only the x and y coordinates are affected, so the z row and columns of the matrix are the same of the identity matrix.

Your equations for x'', y'' and z'' reflect a point through a plane which contains the y axis, so the y axis is unchanged. For a rotation you want the sin and cos arranged in the same order as in the matrix, e.g.:

x'' = z*cos(a) - x*sin(a)
y'' = y
z'' = z*sin(a) + x*cos(a)

gives a rotation about the y axis.

both the matrix and the equations above are in the book as rotating around the x axis. But I just don''t see a correlation between the ordering the vectors in the matrix and the equations.

subnet_rx

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What book? It''s wrong. Those are a Y rot and Z rot respectively.

ahh, just needed someone to say that. It didn't look right to me either, but since I'm the one learning, you really can't correct the teacher. It's in the 3D gaming tutorial series in the Resources section. Link here After looking at it, it doesn't actually say those formulas are the x rotation, but he makes it seem like it is x,y,z respectively for both. Confusing for a newb like me.


subnet_rx

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Edited by - subnet_rx on January 8, 2002 2:44:02 PM