
Geometry : 
Subject: [ggl] Storing the topology of a Polygon
From: Mats Taraldsvik (mats.taraldsvik)
Date: 20110720 16:19:30
Hi,
Often in GIS systems, complex geometries (such as polygons), are (also)
stored as simpler objects (linestrings, circularstrings) to reduce
redundancy and maintain topology.
(from the docs, if I read them correctly:)
* a Polygon contains/points to Rings and Points
* a Ring (only) contains/points to Points
 A Ring is constructed from at least one linestring, I can't maintain
the topology without that information (i.e. identify common linestrings).
  
Ideally, I would save two polygons + topology by looping through them,
looping through their rings, and finally looping through the linestrings
of each ring. If the two polygons share one of the linestrings, I need
to store this once, and when a Ring contains/points to the linestrings
it is constructed from, this is trivial. (The result: A modification in
this shared linestring is refleced in both polygons.)
  
Regards,
Mats
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