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Rotatating line... Linear Algebra question.

Posted on 2004-03-29
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Okay so here's a question. I need an algorithm for rotating a point (p2) about an axis (p1). Here's the spaghetti code I have so far.

Radius = SquareRoot((p2.y - p1.y) ^ 2 + (p2.x - p1.x) ^ 2)
Radians = ArcCos((p1.y - p2.y) / radius) ' Angle between Vector(p1,p2) and unit vector (p1, {0, 1}). Rotating counter clockwise.
Radians = Radians + (2 * ((2 * PI) / 360)) 'Add two degrees to current angle of line
p2.y = (Cos(Radians) * Radius) + p1.y
p2.x = (Cos(Radians) * Radius) + p1.x

The code works fine for angles < 180 degrees. But as soon as I get to say 182 the line moves to an angle of 2 degrees counter clockwise from the unit vector... anyone know a better algorithm for this or how to fix this one to be able to run a full rotation? I need to be able to "add" angles to lines.
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Question by:CyrexCore2k
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by:ozo
ID: 10709272
Radians = atan2(p2.y - p1.y,p1.x - p2.x);
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ozo earned 125 total points
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Radians = atan2(p2.y - p1.y,p2.x - p1.x)

 p2.x = (Sin(Radians) * Radius) + p1.x
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by:CyrexCore2k
ID: 10709644
YES! Thank you!
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