
Geometry : 
Subject: [ggl] question regarding rotate_transformer strategy
From: Jeff Trull (jetrull)
Date: 20111107 13:34:25
I was tracking down a rotation issue and I noticed that the 2D
rotation matrix (around Z) is defined as:
cos(angle), sin(angle), 0,
sin(angle), cos(angle), 0,
0, 0, 1)
But in other sources I have seen it defined as:
cos(angle), sin(angle), 0,
sin(angle), cos(angle), 0,
0, 0, 1)
And in fact, if you imagine a +pi/2 rotation from X [1, 0, 0] to Y [0,
1, 0] the current definition will give:
0, 1, 0,
1, 0, 0,
0, 0, 1
which multiplied by [1, 0, 0] gives [0, 1, 0], which IMO is a pi/2 rotation.
My math is a bit rusty, though. Am I understanding it wrong?
Thanks,
Jeff
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