Calculating angle between 2 vectors

Posted by Error 454 on Game Development See other posts from Game Development or by Error 454
Published on 2011-01-07T02:58:06Z Indexed on 2011/01/07 3:00 UTC
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2d

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ai

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vector

I am working on some movement AI where there are no obstacles and movement is restricted to the XY plane.

I am calculating 2 vectors: v - the direction of ship 1 w - the vector pointing from the position of ship 1 to ship 2

I am then calculating the angle between these two vectors using the standard formula: arccos( v . w / ( |v| |w| ) )

The problem I'm having is the nature of arccos only returning values between 0 and 180. This makes it impossible to determine whether I should turn left or right to face the other ship.

Is there a better way to do this?

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