116 reputation
5
bio website sparr0.livejournal.com
location Atlanta, GA
age 32
visits member for 3 years, 11 months
seen May 2 at 18:05
I am the typical "computer nerd", with skills in a number of programming languages and a wide range of computer hardware and software.

Aug
1
comment How can I count overlapping polygons, resulting in a 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 How can I count overlapping polygons, resulting in a new set of polygons?
Jul
31
revised How can I count overlapping polygons, resulting in a new set of polygons?
memoization
Jul
31
comment How can I count overlapping polygons, resulting in a 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 How can I count overlapping polygons, resulting in a new set of polygons?
rephrase
Jul
30
comment How can I count overlapping polygons, resulting in a new set of polygons?
@AnswerGIS TIN?
Jul
29
awarded  Quorum
Jul
29
awarded  Commentator
Jul
29
comment How can I count overlapping polygons, resulting in a 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 How can I count overlapping polygons, resulting in a 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 How can I count overlapping polygons, resulting in a 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 How can I count overlapping polygons, resulting in a 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 How can I count overlapping polygons, resulting in a 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 How can I count overlapping polygons, resulting in a 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 How can I count overlapping polygons, resulting in a new set of polygons?
Jul
28
asked How can I count overlapping polygons, resulting in a new set of polygons?
Jul
28
answered How can I count overlapping polygons, resulting in a 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