[postgis-users] Re: Question.

[Kevin Neufeld]

Hi ihab,

Unless you write some kind of custom plpgsql function to compute whether 
a line intersects your custom polygons, this is not yet possible with 
the current PostGIS functions.  (I assume your "extruded polygons in 3D" 
are a simple 2D polygon with some height attribute, so the z values are 
all the same).

If you are cleaver enough to write such a function (and I encourage you 
to try), you could use the cube module to quickly winnow your candidate 
set down in the same way the && does in a normal spatial query.

Cheers,
Kevin

eehab hamzeh wrote:
> Hello Kevin
> below is your replay to a question i post before 12 days. i kindly asked you to look to 
> what it again since my building are not 3D boxes they are not squares or rectangles, they are polygons has z values
>  i need to find the lines that intersect these extruded polygons in 3D.
>  
> Thanks 
> ihab 
> 
> 
> Indexes in PostGIS are still only 2D.  Hopefully 3D indexes will be 
> added sometime in the future, but in the meantime, you can perform your 
> 3D query using the cube module.
>  
> http://www.postgresql.org/docs/8.3/static/cube.html
>  
> -- Sample 3D box table
> CREATE TABLE boxes (box box3d);
> INSERT INTO boxes SELECT 'BOX3D(0 0 0,2 2 2)'::box3d;
> INSERT INTO boxes SELECT 'BOX3D(0 4 0,2 6 2)'::box3d;
>  
>  
> -- Sample 3D index
> CREATE INDEX boxes_box_cube_idx ON boxes USING GI
>  ST (
>    cube(
>      cube(
>        cube(ST_XMin(box), ST_XMax(box)),
>        ST_YMin(box),
>        ST_YMax(box)
>      ),
>      ST_ZMin(box),
>      ST_ZMax(box)
>    )
> );
>  
>  
> -- Sample 3D intersect query
> SELECT box
> FROM boxes
> WHERE '(-1,1,1),(3,1,1)'::cube &&
>    cube(
>      cube(
>        cube(ST_XMin(box), ST_XMax(box)),
>        ST_YMin(box),
>        ST_YMax(box)
>      ),
>      ST_ZMin(box),
>      ST_ZMax(box)
>    );
>  
>  
> -- Yields
>          box
> --------------------
>   BOX3D(0 0 0,2 2 2)
> (1 row)
>  
>  
>  
> Cheers,
> Kevin
>  
> eehab hamzeh wrote:
>> Hello,
>> 
>> 
>> I try to use the && operator to select the boxes that intersect one line 
>> in 3d .. i need help to develop the Sql statement,
>> 
>> Select AsText(line_geom) as geom from line where line_geom && 
>> geomFromText(Select astext(the_geom) from boxex)',-1);
>> *> attached is a graph shows how the query result should looks i need just 
>> the red box to be seleced since the line intersect only the red box and 
>> not the another box which is lower than the line height.
>> 
>> Thanks
>> 
>> *
> 
> *
> *
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