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Area of a general n-sided polygon

  1. Jan 18, 2014 #1
    Finding the area of an irregular polygon with n side is quite easy when we are given the length of all of the n sides and the length of (n-3) specific diagonals. This way, we get (n-2) triangles whose areas can be calculated using Heron's formula and then added up.
    attachment.php?attachmentid=65765&stc=1&d=1390046811.png
    But what if the length of the (n-3) diagonals provided doesn't make (n-2) triangles, such as this case:
    attachment.php?attachmentid=65766&stc=1&d=1390046811.png
    The polygon is still fully determined by the given measurements, but calculating the area is difficult.
    Is there some sort of generic formula for such cases? Like maybe using matrices. :D

    I thought of making a mobile application to help real-estates peoples calculate the area of lands, and came-up with this question.
    Thank you.
     

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  3. Jan 18, 2014 #2

    SteamKing

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    There are several different methods of finding areas of general polygons:

    http://en.wikipedia.org/wiki/Polygon

    When you say 'real estate peoples', are you referring to land surveyors or someone else?
     
  4. Jan 18, 2014 #3

    There is no formula for finding area when n sides and n-3 diagonals are known.
    The surveyors formula seems to be the best way to go. So from the given information, I should somehow find the coordinates of all the vertices and also sort them counter clockwise or clockwise.

    By real state peoples I just meant anyone who is involved in buying or selling of lands.
     
  5. Jan 18, 2014 #4

    SteamKing

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    Well, in the US, the land surveyor is the professional who confirms and measures the boundaries of a particular plot of land. There is usually a legal description of the land produced for a deed of title to the land, which would contain the area enclosed by these boundaries.

    The proper orientation for your vertex coordinates is counterclockwise to calculate the positive area of the figure. If you use a clockwise orientation, the result will be a negative area. This comes in handy if you want to evaluate the area of complex, non-convex polygons, say a polygon with a hole in it.
     
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