[postgis-users] PostGIS Capabilities

[Tyler Mitchell]

> Thanks. It works. 

Right on - I thought we were just talking theory, nice to see 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;

This takes me back to the question of how you define "on the line".  I 
would bet (others can verify) that if the bridge point did actually fall 
exactly on the road line vector (highly unlikely in my opinion) then this 
should work. 

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

Interesting.  I then assume that the ArcGIS buffers your points and then 
looks for the intersections.  It's really a matter of scale which.  Zoom 
in as far as you possibly can and tell me if the point and line directly 
overlap.  I assume that they do not!  This brings up the question of 
whether or not ArcGIS "should" work or not.  But we're not taught to 
question ;)

In my opinion, the user should have to think about a search radius between 
features like this and not default to software to guess. 

This reminds me of an old problem I had with Arcview 3 - we were 
programmatically grabbing and zooming to the extent of features.  We hit 
lots of problems, only to finally discover that AV was extending the 
extent so that it "looked good" on the screen.  Oh well, I've heard that 
legacy GIS applications like AV and Arc Map are still good for some tasks 
:)

Tyler
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-users/attachments/20040219/34356b73/attachment.html>