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I have a set of Points representing building footprints (black in the image below). I also have Points (building address Points) that I know lie inside the building footprints (green).

I'm searching for the name of a reverse convex hull analysis(?). Imagine blowing up a balloon starting at green Points.

I will then use the results to give each black Point an address (which is stored in the green Point)

enter image description here

tinlyx
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BERA
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  • Could you instead find the distance from the green point to the further black point, then construct a circle with bigger radius than that, then apply regular convex hull analysis? – Ian Miller Nov 30 '16 at 13:08
  • I dont Think that will work since the convex hull will possibly include black Points from nearby other Buildings. – BERA Nov 30 '16 at 13:11
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    Can you have concave building interiors? You mention convex hulls but I can think of many buildings which are concave on the inside. – Ian Miller Nov 30 '16 at 13:15
  • Yes it is possible. – BERA Nov 30 '16 at 13:20
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    But if the interior doesn't have to be convex, your hull is not well-defined. In your example, the buildings might as well be joined at the bottom to form a "U". – Dominik Nov 30 '16 at 13:27
  • You are correct. It is probably not possible to accomplish what i want. – BERA Nov 30 '16 at 13:31
  • Have a look at the Alpha-shapes. –  Nov 30 '16 at 13:31

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If the black points describing the building footprint come to you in a cyclic order (that's likely) then you can easily form the polygon that describes the building. (If the building is convex this will be the convex hull.)

Then loop on the green points and use a point in polygon algorithm to assign an address to each building (and hence to each black point).

I note in your profile that you do a lot of GIS. Check to see if your software has tools for your problem.

Ethan Bolker
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  • Cyclic order = For example point nr 1,2,3,4,5 is first building, 6,7,8,9,10,11,12 etc. second? How can i know which Point is the first/last for each building? – BERA Nov 30 '16 at 14:09
  • @BERA "Cyclic order" means that for each building you have a list of the footprint points that starts somewhere and walks around the walls until it gets back to the starting point. It doesn't matter where the list starts. You can assume that when it ends you go back to the start. If you don't know which black points belong to which buildings you can't solve the problem. In the picture in your question it might be that the 10 points in the top half describe one building and the 10 in the bottom another. – Ethan Bolker Nov 30 '16 at 14:15