[geos-devel] How to build a multipolygon from a list of rings?

[Frederik Ramm]

Hi,

zhuliangxiong at hotmail.com wrote:
> how could i build a MultiPolygon from a list of rings  directly? 

Have you tried using the Polygonizer class to create a collection of
polygons from your data, then make a multipolygon from that?

> It is 
> hard for me to find out the relationship of holes and out rings.

I had a similar situation once and cursed GEOS for not allowing me to
find out which ring is inside another - I first had to convert all rings
to polygons individually, then I could check each of these polygons
(using the "contains" method) whether it was contained in any of the
others, and this then allowed me to construct a proper createPolygon
call (or multiple of those).

Bye
Frederik