Geometry Boost List: [ggl] union/intersection of multi-polygons

Subject: [ggl] union/intersection of multi-polygons
From: Bruno Lalande (bruno.lalande)
Date: 2010-03-10 04:42:06

Hi Barend,

Sorry for the very late answer on this, this email got lost somehow.

I'm not knowledgeable at all on this kind of decision, but as a GIS
newbie I would say it doesn't make sense to me as well to detect
internal intersections of 2 self-intersecting multipolygons when
trying to intersect them with each other. We're really trying to
intersect to distinct entities, whatever happens *inside* them is not
relevant.

If the user really wants to do that, maybe we could provide a function
that would split multipolygons back into several polygons. The
resulting concept could be called "polygon_group" or even "polygons",
and its fundamental difference with a multipolygon would be that when
a binary operation is called on 2 polygon groups, the operation would
actually be applied on all the polygons listed. That is, if you
intersect 2 polygon groups, one with 2 polygons and one with 3, you're
actually asking to intersect 5 polygons in total.

Something like that... makes sense?

Regards
Bruno