[OSM-dev] Polygons in OSM don't necessarily comply to simple feature specification

Frederik Ramm frederik at remote.org
Wed Apr 16 23:15:16 BST 2008


Hi,

> The only exceptions apparently  
> being that self-intersecting polygons are allowed in OSM. 

The wiki page you cited says "In general, a 2D geometry is simple if
it contains no self-intersection." - what do they mean by "2D
geometry"? Specifically, would a self-intersecting *line* be allowed?
(I like to think of points as 0D, lines as 1D, and areas as 2D but I
have a feeling the GIS people might view this differently?)

Self-intersecting *lines* may indeed make sense, think of an "8"
shaped narrow-gauge railway in a park. For a data format without
topology, the "8" could be drawn in a way that would not intersect
but if you intend to keep topology intact then you need the
intersection.

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"





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