Faster polygon combining #681
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The
combine_polygons_belowoption significantly slows tile generation (#270). In #383 we moved to faster code but it's still not especially fast.This PR further improves it by using a neat bit of code from boostorg/geometry#947 (comment). It also successfully merges more adjoining polygons. Newer Boost has
merge_elementsbut we can't rely on users having that yet.It also removes a bit of template-y indirection by replacing CheckNextObjectAndMerge and MergeIntersecting with a simple while loop.
For Reims using my 2014 Mac mini:
No combine_polygons_below: 12s
Using combine_polygons_below, current master: 122s
Using combine_polygons_below, this PR: 80s
There's clearly still room for improvement (maybe using an rtree to quickly identify polygons that intersect, and only unioning those?) but this is a worthwhile step forward.