RE: [postgis] 'real' contains, touches, overlaps etc.

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RE: [postgis] 'real' contains, touches, overlaps etc.

Martin Davis-2
You're right, Manuel, conformance to the OGC spec requires relationship
operators that use the DE-9IM model (that is, that understand the difference
between exterior, interior and boundary).    There's also some other subtle
and not-so-subtle issues that need to be addressed in a production-quality
spatial library:

* Using a finite-precision numerical representation (eg floating point
or integers) can cause a naive implementation to fail badly on certain kinds
of input.  This can be avoided by using robust geometric algorithms.
* Some kind of spatial indexing or other efficient spatial data
structure need to be implemented if the code is to be usable on inputs with
anything more than a small number of points.
* The OGC spec has some subtle with how the definition of the spatial
data types interacts with the relationship operators.  A good implementation
should specify how it handles these issues.

JTS is designed to address these issues.  If you're interested in reading
the design specification, which elaborates on these issues and other aspects
of JTS, you can find it at  http://www.vividsolutions.com/jts/jtshome.htm



Martin Davis, Senior Technical Specialist
Vivid Solutions Inc.
Suite #1A-2328 Government Street   Victoria, B.C.   V8T 5G5
Phone: (250) 385 6040    Fax: (250) 385 6046
EMail: [hidden email]  Web: www.vividsolutions.com


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Re: [postgis] 'real' contains, touches, overlaps etc.

Manuel Weindorf
Hi Martin,

thanks for the hints. As I looked at the details I have to agree completely
with you. I'm looking forward to see what you've done in JTS and how it can
be ported to C/C++.

Manuel

> You're right, Manuel, conformance to the OGC spec requires relationship
> operators that use the DE-9IM model (that is, that understand the
> difference between exterior, interior and boundary).    There's also some
> other subtle and not-so-subtle issues that need to be addressed in a
> production-quality spatial library:
>
> * Using a finite-precision numerical representation (eg floating point
> or integers) can cause a naive implementation to fail badly on certain
> kinds of input.  This can be avoided by using robust geometric algorithms.
> * Some kind of spatial indexing or other efficient spatial data
> structure need to be implemented if the code is to be usable on inputs with
> anything more than a small number of points.
> * The OGC spec has some subtle with how the definition of the spatial
> data types interacts with the relationship operators.  A good
> implementation should specify how it handles these issues.
>
> JTS is designed to address these issues.  If you're interested in reading
> the design specification, which elaborates on these issues and other
> aspects of JTS, you can find it at
> http://www.vividsolutions.com/jts/jtshome.htm


--
Manuel Weindorf ([hidden email])
Institut fuer Photogrammetrie und Fernerkundung, Universitaet Karlsruhe
Postfach 6980 D-76128 Karlsruhe, Tel. +49 721 608-6010 Fax +49 721 608-8450
http://www-ipf.bau-verm.uni-karlsruhe.de

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