[postgis-users] 3D question
Paul Ramsey
pramsey at refractions.net
Fri Sep 17 14:46:23 PDT 2004
PostGIS is 2.5d -- we store Z coordinates, but little of the
functionality is 3d-aware. There are a few lenght_* functions that
explicitly use the 3rd coordinate. Making the index 3d aware is
possible. Making most of hte other functions 3d aware is quite a pile of
work due to the maths and heuristics involved.
Dorian Bolivar wrote:
> Hi,
>
> We're trying to use PostGIS for a 3D environment, but it's not working
> as expected. We first inserted some points with X, Y and Z
> coordinates, then tried to select a spatial region using BOX3D(), but
> it seems that this function works only in 2D mode. We also tried some
> distance() calculations, and it also worked in 2D.
>
> We read the manual and played with the force_3d() function, but it was
> useless. Some of the queries we entered (we tried these both with
> points inserted with and without the force_3d() function):
>
> Distance:
>
> select geom from geom_test where distance(geom, 'POINT(1 1 1)') > 1.5;
>
> Box3d:
>
> select geom from geom_test where geom && 'BOX3D(0.25 -0.25 -0.25,0.75
> 0.25 0.25)'::box3d and distance(geom, 'POINT(0.5 0 0)') < 0.2;
>
> Playing with force_3d():
>
> select geom from geom_test where distance(geom, force_3d('POINT(1 0
> 1)')::geometry) > 1;
>
>
> Thanks a lot,
>
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