[postgis-devel] Dropped DM (Time) dimension with intersections

[Paul Ramsey]

Perhaps elabourate on what better 3D support would be? There's the
surface object hanging around. There's the issue of maintaining higher
dimensional coordinates through lower dimensional transforms (which
you saw the result of a few days ago). There's elabourating the
complete set of 3D objects and relationships (gulp).

It's not clear to me what is the "low hanging fruit" that will make 3D
users happiest in the shortest time.

P.

On Tue, Oct 7, 2008 at 8:54 AM, Obe, Regina <robe.dnd at cityofboston.gov> wrote:
> Margie,
>
> Unfortunately I think the answer is no.  Most of the work going on in 1.4 is
> to improve speed of existing functionality and reorganize the source to make
> it more maintainable.
>
> Someone please correct me if I am wrong.
>
> I for one would be very elated if we had better 3D support since CityGML and
> similar initiatives are becoming more of a hot topic around here.
>
> Thanks,
> Regina
> ________________________________
> From: postgis-devel-bounces at postgis.refractions.net
> [mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of
> Huntington, Margaret (US SSA)
> Sent: Tuesday, October 07, 2008 11:47 AM
> To: postgis-devel at postgis.refractions.net
> Subject: [postgis-devel] Dropped DM (Time) dimension with intersections
>
> Hello,
>
>     Currently I'm using PostGIS 1.3.3.  From past discussions and from
> testing, both the st_intersection st_extend methods return 2D results with
> 4D input geometries.  As a temporary work-around, I had hoped
> st_intersection might work with 3DM geometries.  (Plan was to interpolate
> the altitude value within the function call if PostGIS could calculate the
> time dimension).   I found time components are also dropped by
> st_intersection with 3DM geometries.  I abandoned usage of 4D bounding boxes
> since these too effectively degrade 4D geometries down to 2D geometries
> (altitude and time are zeroed out).
>
>     polyGeometry geometry;
>
>     bbGeometry geometry;
>
>     intersectionGeometry geometry;
>
>     coorddims smallint;
>
>            -- both polygon and linestring have an expected zmflag value of 1
>
>            polyGeometry := 'SRID=4326;POLYGONM((0 0 0, 0 10 4, 10 10 4, 10 0
> 0, 0 0 0))'::geometry;
>
>            bbGeometry := 'SRID=4326;LINESTRINGM(0 0 1.5, 10 10
> 2)'::geometry;
>
>            intersectionGeometry := st_intersection(polyGeometry,
> bbGeometry);
>
>            -- st_intersection method drops the time dimension; zmflag value
> of 0
>
>            coorddims := st_zmflag(intersectionGeometry);
>
> If I were to download the subversion snapshot, the current 1.4 version,
> might st_intersection work with either 3DM or 4D geometries?  Are bounding
> boxed or st_extend improved for either 3DM or 4D geometries?  I had
> incorporated polygons only as a possible work-around to the bounding box and
> st_extend 2D limitations.
>
> Margie
>
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