[postgis-users] Polygons: the unstable foundation of spatial modeling

[bartvde at xs4all.nl]

Hi list,

the following article dating from October 2003 deals with a comparison of
polygon definitions (and especially the boundary between valid and
invalid) in several Spatial DBMS's, and also PostGIS 0.6.2.

http://www.vz.geodan.nl/users/bart/17-VanOosterom_Polygons.pdf

Any comments on this? I can imagine a lot has changed since version 0.6.2
regarding this subject?

Best regards,
Bart

Summary:
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Spatial models are often based on polygons both in 2D and 3D. Many Geo-ICT
products support spatial data types, such as the polygon, based on the
OpenGIS ‘Simple Features Specification’. OpenGIS and ISO have an agreement
to harmonize their specifications and standards. In this paper we discuss
the relevant aspects related to polygons in these standards and compare
several implementations. A quite exhaustive set of test polygons (with
holes) has been developed. The test results reveal significant differences
in the implementations, which causes interoperability problems. Part of
these differences can be explained by different interpretations
(definitions) of the OpenGIS and ISO standards (do not have an equal
polygon
definition). Another part of these differences is due to typical
implementation issues, such as alternative methods for handling
tolerances. Based on these experiences we propose an unambiguous
definition for polygons, which makes polygons again the stable foundation
it is supposed to be in spatial modelling and analysis.