
Geometry : 
Subject: [geometry] Negative distance?
From: Volker Schöch (vschoech_at_[hidden])
Date: 20120308 02:47:03
Hi,
I am seeing negative results from the distance algorithm with boost::geometry::distance(MultiPolygon, Point). I wonder if this is a problem in my code, or a bug in GGL, or by design  and in the latter case, what's the meaning of negative distances?
The boost::geometry documentation says:
> The function distance implements function Distance from the OGC Simple Feature Specification.
The OGC Simple Feature Specification says:
> Distance (anotherGeometry: Geometry):Double  Returns the shortest distance between any two Points in the two geometric objects as calculated in the spatial reference system of this geometric object. Because the geometries are closed, it is possible to find a point on each geometric object involved, such that the distance between these 2 points is the returned distance between their geometric objects.
I don't find my question explicitly answered there, but since in mathematical geometry distances are usually nonnegative and there is no mentioning or explanation of why and how OGC would define negative distances, I assume it may be a bug?
I am using boost 1.48.0, my polygon type is oriented counterclockwise and not closed, my point type is based on int.
Regards
Volker
 Volker Schöch  vschoech_at_[hidden] Senior Software Engineer thinkcell Software GmbH  Chausseestr. 8/E  10115 Berlin  Germany http://www.thinkcell.com  phone +49 30 66647310  US phone +1 800 891 8091 Amtsgericht BerlinCharlottenburg, HRB 85229  European Union VAT Id DE813474306 Directors: Dr. Markus Hannebauer, Dr. Arno Schoedl
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