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

[Obe, Regina]

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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