[postgis-users] intersect operation in 3d?

[Hugh Stimson]

Thanks for your reply Ralf.

Since posting my query I've found this helpful chart of functions with their 2.5d support:

http://postgis.refractions.net/docs/ch08.html#PostGIS_TypeFunctionMatrix

According to that, the ST_Intersects and ST_Intersection functions aren't yet 2.5d enabled.  So I'm guessing that means that while they will accept data with an assigned Z, as you suggest, only the x/y dimensions will be considered in determining if they are coincident.

That isn't sufficient for the application I'm working on, I need to be able to distinguish the case where one object passes over another one without actually touching. The shapes involved are complex enough that using a simple elevation rule to pre-filter can't account for all possible situations.

Might have to shell out the big bucks for an ESRI license. Ouch.

cheers, Hugh

> Hi Hugh,
>
> all functions in PostGIS will work on 2.5D data. So you have to add an extra
> condition for your z-range.
>
> Gr
> Ralf
>
> Am Freitag 16 Juli 2010, 23:32:03 schrieb Hugh Stimson:
>> Hi PostGIS folks,
>>
>> I'm trying to find a way to read two 3-dimensional polygons and test if
>> they intersect. It's for a radar-bird-tracking application. I'm hoping
>> that PostGIS is a solution.
>>
>> I've been scanning the Mailing list archives, and I gather that at least
>> some of the spatial operations which PostGIS provides are 3d-enabled.
>> Which surprises me, as my understanding was that PostGIS spatial
>> operations descend from the Java Topological Suite via GEOS, and JTS
>> advertises itself as being specifically for 2-d linear modelling.
>>
>> Could I count on the ST_Intersects function to work with 3d data? Would
>> there likely be any special considerations for 3d?
>>
>> http://postgis.refractions.net/documentation/manual-1.5/ST_Intersects.html
>>
>> cheers,
>>
>> Hugh

-- 
Hugh Stimson / 778.373.1024 / hughstimson.org