[postgis-users] PostGIS Capabilities

[Jong S. Lee]

Tyler:

Thanks. It works.  Could you tell me why the following SQL does not working?

SELECT bridge.gid
FROM bridge, highway
WHERE intersects(bridge.the_geom, highway.the_geom) and highway.gid = 49;

For your information, the operation with "intersecting" in ArcGIS worked.

Jong.

Tyler Mitchell wrote:

>
> Hi Jong,
>
> > Wow... Amazing PostGIS!!
>
> That's the spirit!
>
> > Question:     How to select points on the line?  For example, how to
> > select the bridges on the highway?
>
> Good practical question - I get excited thinking about just how easy 
> this is to do (with no licensing fees involved!).
>
> I think it will depend on how you define "on the line".  Do the bridge 
> share the same point as a node in your line?  Or (as I assume is the 
> case) are your points within a certain distance from a line (i.e. < 10 
> metres)?  
>
> If the latter, then something like this should do the trick:
>
> SELECT bridges.name
> FROM bridges, highways
> WHERE DISTANCE(bridges.geometrycolumn, highways.geometrycolumn) < 10;
>
> There are ways to optimize this query, I just gave you the most basic.
>
> Hope that helps you out.
>
> Tyler
>
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-- 
Jong Sung Lee, Graduate Research Assistant
Department of Urban and Regional Planning
University of Illinois at Urbana-Champaign
111 Temple Hoyne Buell Hall
611 East Loredo Taft Dr.
Champaign, IL  61820

Tel:(217)244-6564 
E-mail:jonglee1 at uiuc.edu

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