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Aug
1
comment Counting overlapping polygons in GeoJSON to result in new set of polygons?
@whuber which software package are you referring to? Union, as a simple boolean operation, is available in almost every vector and GIS application. In the ones I've tried, the result is just another [multi]polygon, without the data I'm looking for.
Jul
31
answered Counting overlapping polygons in GeoJSON to result in new set of polygons?
Jul
31
revised Counting overlapping polygons in GeoJSON to result in new set of polygons?
memoization
Jul
31
comment Counting overlapping polygons in GeoJSON to result in new set of polygons?
Say I have 5 polygons, A B C D E, and I want to know the region covered by at least 3 of them. I will use | to represent union and & to represent intersection. Here are the operations required: (A&B&C)|(A&B&D)|(A&B&E)|(A&C&D)|(A&C&E)|(A&D&E)|(B&C&D)|(B&C&E)|(B&D&E)|(C&D&E) 20 intersection operations (15 with memoization), 10 unions. For 20 polygons, the 10-or-more case requires 1662804 intersections and 184756 unions. Doing this with 100 polygons is infeasible. With 1000 impossible. I need a better algorithm if I'm going to script this myself.
Jul
30
awarded  Editor
Jul
30
revised Counting overlapping polygons in GeoJSON to result in new set of polygons?
rephrase
Jul
30
comment Counting overlapping polygons in GeoJSON to result in new set of polygons?
@AnswerGIS TIN?
Jul
29
awarded  Quorum
Jul
29
awarded  Commentator
Jul
29
comment Counting overlapping polygons in GeoJSON to result in new set of polygons?
I am comfortable coding in Python and am learning to use QGIS, but I'm still not sure how to approach this problem even in that context.
Jul
29
comment Counting overlapping polygons in GeoJSON to result in new set of polygons?
I think doing a complete set of intersections as you suggest might produce prohibitively many result polygons (millions, in some cases).
Jul
29
comment Counting overlapping polygons in GeoJSON to result in new set of polygons?
@AlexandreNeto that does not mesh with the suggested and practiced self-answer methods on other SE sites. This is not part of my question. It is an answer. If anything, I should have put "This approach loses precision" in a comment on this answer.
Jul
29
comment Counting overlapping polygons in GeoJSON to result in new set of polygons?
@AlexandreNeto can you elaborate on this? I received two different answers to this question when I asked it outside of SE. I posted those answers here to avoid others' wasting their time posting answers I already had (and that weren't appropriate for my situation).
Jul
29
comment Counting overlapping polygons in GeoJSON to result in new set of polygons?
@PolyGeo converting it is definitely an option. I think converting to TopoJSON or even SHP or another format would be pretty easy to automate.
Jul
28
awarded  Student
Jul
28
comment Counting overlapping polygons in GeoJSON to result in new set of polygons?
This site used rasterization and then binning on a hex grid to produce results similar to what I'm looking for: bostonography.com/2012/…
Jul
28
answered Counting overlapping polygons in GeoJSON to result in new set of polygons?
Jul
28
asked Counting overlapping polygons in GeoJSON to result in new set of polygons?
Jul
28
answered Counting overlapping polygons in GeoJSON to result in new set of polygons?
Apr
5
comment What format is this data in?
fixed width plus delimiters is easy to deal with, just tell excel there's a one-character column where the "+"s are and then hide those columns