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Math Help - Labelling the Outer Points of a Pentagram

  1. #1
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    Labelling the Outer Points of a Pentagram

    Hi,

    I'm trying to program an outer point labelling system for pentagrams and I'm having trouble with the logic.

    I have 5 pairs of outer x & y coordinates
    I have 5 pairs of inner x & y coordinates

    I have decided that point "A" is the outer x & y coordinate pair that has an x value closest to the x value of the center of the inner pentagon. That's easy. The center just being the average of the 5 inner pairs.

    I would like the outer points to be labelled clockwise, B, C, D & E.

    What logic can I use to determine which point is which?

    Any help is appreciated.

    Thanks
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  2. #2
    MHF Contributor
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    Re: Labelling the Outer Points of a Pentagram

    Hey Stockgoblin.

    If you want to create a clock-wise ordering of points then you need to calculate the convex hull and reverse the order obtained by that algorithm (which creates an ordered list of points that is counter-clockwise in order).

    For your problem, you have a 2D version which is a lot simpler than three or higher dimensions.
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