[postgis-devel] [PostGIS] #2034: ST_3DClosestPoint with mixed dimensionality in input values

PostGIS trac at osgeo.org
Sat Oct 6 18:36:06 PDT 2012

#2034: ST_3DClosestPoint with mixed dimensionality in input values
 Reporter:  nicklas      |       Owner:  nicklas      
     Type:  enhancement  |      Status:  new          
 Priority:  medium       |   Milestone:  PostGIS 2.1.0
Component:  postgis      |     Version:  trunk        
 Keywords:               |  

Comment(by robe):

 just my 2c.  I agree that ST_ClosestPoint should ALWAYS return a 2D point.
 That's what we say it does.  That's what it should. In the case of
 ST_ClosestPoint, there is no ambiguity even with 2D / 3D since it will
 always ignore the Z anyway.

 For the 3D Closest Point.  It should always return a 3D point and in case
 of 3d/2D operations -- that operation should simply be undefined.

 My concern with making any assumptions here is that it's well undefined
 and open to endless debate.  The idea of making a 2D point into a 3D line
 is just wrong because it's no longer a point and you end up with a
 shortest line being mixed dimension.  The idea of a 2D point existing in
 3D space (with 0 for Z) is also wrong. NULL (undefined) is not the same as
 infinity nor should it be.

Ticket URL: <http://trac.osgeo.org/postgis/ticket/2034#comment:7>
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