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Scatter Chart Boundaries

  1. #1
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    Question Scatter Chart Boundaries

    Not even sure how to explain this, but I'm going to give it a shot. I'm fairly confident in my VBA skills, but I'm not sure on the methodology to get what I'm after.

    I'm trying to determine the points on a scatter graph that define the boundaries of that scatter graph.

    An example might help illustrate by issue. I have the following 12 points:

    1: 0, 1.5
    2: 1, 5
    3: 2.5, 5.5
    4: 3, 6.2
    5: 4, 5.5
    6: 5.5, 5.8
    7: 5.2, 2.5
    8: 7, 0.3
    9: 3, 2.5
    10: 4.3, 1
    11: 2.5, 0
    12: 1.5, 1.3

    If you graph them, you can visually see that points 1, 2, 4, 6, 8, 11 and back to 1 define the area.
    scatter graph example image

    So how do I do that? Any help would be greatly appreciated.

  2. #2
    Forum Moderator Richard Buttrey's Avatar
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    Re: Scatter Chart Boundaries

    Does the attached help.

    It uses Data Filter Advanced to output all the plot points which have >= n-2 neighbouring co-ordinates for each of the x & y co-ordinates. Where n = the number of plots

    i.e There are always at least 4 which are identified by the maximum and minimum co-ordinates. Then there could in theory be an infinite number of other points. These are any points where there are at least n-2 neighbours. In this example these are points 2 & 6.

    HTH
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    Richard Buttrey

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  3. #3
    Forum Guru Andy Pope's Avatar
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    Re: Scatter Chart Boundaries

    VBA solution. Set the TightFit property to true.

    http://www.andypope.info/charts/convexhull.htm
    Cheers
    Andy
    www.andypope.info

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