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I have been looking everywhere trying to find out how to convert an angle in radians (expressed as -Pi to Pi) to a heading vector.

The only [x,y] answer I have found is, [cos(angle), sin(angle)] , however, this doesn't work! Or am I missing something?

I just want a vector pointing at a direction of a specified angle, and for it to have a magnitude of 1, such is called a "heading vector" I believe. At least it is in the various game code I look at.

CLARIFICATION: A heading vector is a vector with a magnitude of 1 with the start at 0, and the end (the arrowhead) at some value within a unit circle. A heading vector is a way of showing direction as a vector. I want to take an angle and express it as a vector, however, people seem to just be telling me how to do unit conversions.

I appreciate you trying to be helpful, however, hopefully these clarifications will guide others to giving more fitting responses.

Thanks.

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An angle in standard position has one side on the positive x-axis, and is measured counter-clockwise. The angle for heading/bearing is measured from the positive y-axis, clockwise. –  The Chaz 2.0 Aug 9 '12 at 23:56
    
This does not answer my question. –  José Aug 10 '12 at 2:04
    
"...this doesn't work!" - you haven't said why... –  J. M. Aug 10 '12 at 2:10
    
Let's stop using the word "heading". See the picture in the top right for visuals of "initial" and "terminal" sides of an angle. If you want a point that is one unit away from the origin that makes an angle $\theta$ with the positive x-axis when connected to the origin, that point is (cos $\theta$, sin $\theta$). If you want a vector, use brackets instead of parenthesis. –  The Chaz 2.0 Aug 10 '12 at 2:18
    
J.M. - It doesn't work, because I have tried it and it gives strange answers!Funny I can't find a solution to a seemingly simple problem... –  José Aug 10 '12 at 13:25
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2 Answers 2

Your information is correct.

If you have an angle (A), in radians, in the range -Pi to Pi, then convert it to a vector (V) with:-

V.x = cos(A)

V.y = sin(A)

(The inverse is A = atan2 ( V.y, V.x ) )

If it doesn't work in your games code you should be looking for a typing error, or other silly little bug. Its not the maths.

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To convert radians to degrees, you multiply by $\frac {180}{\pi}$. The standard positions for angles and headings are different, as The Chaz has commented. To go from a regular angle of $\theta$ to a heading, the heading is $\frac {\pi}2 - \theta$ in radians or $90^\circ -\theta$ in degrees.

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