[postgis-users] 3D support in PostGIS

[Paul Ramsey]

On Jan 28, 2008, at 4:56 AM, Olivier Tournaire wrote:

> 1. As far as I know, PostGIS is ale to store 3D data. Am I right ?

It can store z-variants of point, line, polygon, multipoint,  
multiline, multipolygon.

> 2. If I create a spatial index on a table which contains 3D  
> geometries, is it a real 3D index, or the objects are projected onto  
> the ground and the the index is built with this projection ?

Indexes are 2-d.

> 3. Last, but not least, is it possible to have operations on  
> geometries in a 3D framework. For example, it I test if the point  
> (0,0,50) is within the polygon ( (-10,-10,0) (-10,10,0) (10,10,0)  
> (10,-10,0) ), what is the answer ? In other words, is the result  
> obtained with taking into account the Z coordinate or not ?

Z-values are ignored in tests, and occasionally used in building  
resultants for things like intersections.

P