[postgis-users] Definition of St_Distance in case of 2 non point geometries

[Nicklas Avén]

If I understand you right your assumption is true. 


What makes you wondering?


In 2d you will always get the distance to a vertexpoint in at least one of the two geometries.


You can use ST_ShortestLine to see between what points the distance is calculated.


So:


SELECT ST_Distance('LINESTRING(1 1, 1 10)'::geometry, 'LINESTRING(2 5, 10 5)'::geometry);
 returns 1
and 
SELECT ST_AsText(ST_ShortestLine('LINESTRING(1 1, 1 10)'::geometry, 'LINESTRING(2 5, 10 5)'::geometry));
returns 'LINESTRING(1 5, 2 5)'::geometry


geography type calculations is of course another story.




HTH


Nicklas







2013-10-18 Peter Hopfgartner  wrote:

I took it for granted, that ST_Distance between two two dimensional 
>geometries followes the definition of
>
>dist(A, B) = inf(d(a,b)), where a is an arbitrary point in set A and b 
>an arbitrary point in set B and d() is the euclidean distance
>
>For some reason I'm now wondering if my assumption is true.
>
>Thanks for your patience,
>
>Peter
>
>-- 
>Peter Hopfgartner
>R3 GIS
>
>web  : http://www.r3-gis.com
>
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