2D Euclidean vector rotations
I have a euclidean vector a sitting at the coordinates (0, 1).
I want to rotate a by 90 degrees (clockwise) around the origin: (0, 0).
If I have a proper understanding of how this should work, the resultant (x, y) coordinates after the rotation should be (1, 0).
If I were to rotate it by 45 degrees (still clockwise) instead, I would have expected the resultant coordinates to be (0.707, 0.707).
theta = deg2rad(angle);
cs = cos(theta);
sn = sin(theta);
x = x * cs - y * sn;
y = x * sn + y * cs;
Using the above code, with an angle value of 90.0 degrees, the resultant coordinates are: (-1, 1).
And I am so damn confused.
The examples seen in the following links represent the same formula shown above surely?
What have I done wrong? Or have I misunderstood how a vector is to be rotated?
Answer
Rotating a vector 90 degrees is particularily simple.
(x, y) rotated 90 degrees around (0, 0) is (-y, x).
If you want to rotate clockwise, you simply do it the other way around, getting (y, -x).