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Thread: Rotating a Rectangle Help

  1. #1
    Newbie
    Joined
    Aug 2008
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    Rotating a Rectangle Help

    Hello,
    I'm trying to work on rotating a rectangle for some computer code. I know the top left and right co-ordinates and the rectangle size, but I'm trying to figure out how I'd determine the relative co-ordinates of the bottom points that would be joined to create the rectangle. Is there a formula for this?

    I haven't done maths in a while so please excuse me if this is straightforward!

    Thanks
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  2. #2
    Super Member
    Joined
    Jun 2008
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    792
    You can use a rotation matrix.

    Suppose you have a point P(x,y). Let the image point be B(x`,y`) after a rotation of $\displaystyle \theta$ radians. The coordinates of the image point can be found by matrix multiplication:

    $\displaystyle \left[ {\begin{array}{*{20}c}
    {\cos{\theta}} & {-\sin{\theta}} \\
    {\sin{\theta}} & {\cos{\theta}} \\
    \end{array}}\right]
    \left[ {\begin{array}{*{20}c}
    {x} \\
    {y} \\
    \end{array}} \right] =
    \left[ {\begin{array}{*{20}c}
    {x'} \\
    {y'} \\
    \end{array}} \right]

    $
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