[postgis-devel] [PostGIS] #231: New distance-calculations proposal

[PostGIS]

#231: New distance-calculations proposal
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  Reporter:  nicklas      |       Owner:  robe         
      Type:  enhancement  |      Status:  assigned     
  Priority:  medium       |   Milestone:  postgis 1.5.0
 Component:  postgis      |     Version:               
Resolution:               |    Keywords:               
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Comment (by robe):

 Ah yes its good we can figure out how a black box works by interrogating
 it.

 Speaking of ST_ShortestLine and ST_LongestLine, as much as I hate non-
 symmetric functions and introducing trivial functions, I really think we
 should have a ST_ClosestPoint and ST_FurthestPoint.
 Which would be wrappers like the below (might be better to do them in C
 than as SQL wrappers)

 {{{
 ST_ClosestPoint(A,B) => SELECT ST_StartPoint(ST_ShortestLine(A,B));
 ST_FurthestPoint(A,B) => SELECT ST_StartPoint(ST_LongestLine(A,B));
 }}}


 And as you can see would return the respective closest/furthest point on A
 from geometry B.  The reason I think we need these is because I think 80%
 of the time people will just take our 2 gifts for the price of 1 and pull
 out one of them and discard the other.  At least that's what in 80% of my
 usecases I would do.

 Its also a vocabulary thing -- I think people think in terms of closest
 furthest, nearest furthest. So when you say shortest line/longest line --
 I think people will be scratching their heads, where as if you say "This
 will give you the closest point", then lightbulbs will go off.  The
 longest and shortest should of course stay since when you need both points
 at the same time you would use those.

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/231#comment:22>
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