[postgis-users] compute "difference" between two roads

[Stephen Woodbridge]

cesare,

I think it would be helpful if you could post the geomerty for a 
reference line, a line you would expect in the difference set and a line 
that you would expect to get filtered out (likely the same as the 
reference line).

Then it will be easier to see what data you are dealing with and how to 
construct an appropriate query. So a dump of a table(s) with with a few 
lines that meet these requirements would be helpful.

-Steve

c. m. wrote:
> hi michael,
> thanks a lot that you're trying to help me. i'm quite new to the whole 
> thing. do you mean small db table's e.g. concerning one street?
> 
> cesare
> 
> 
>> From: Michael Fuhr <mike at fuhr.org>
>> Reply-To: PostGIS Users Discussion 
>> <postgis-users at postgis.refractions.net>
>> To: PostGIS Users Discussion <postgis-users at postgis.refractions.net>
>> Subject: Re: [postgis-users] compute "difference" between two roads
>> Date: Fri, 8 Sep 2006 05:30:49 -0600
>>
>> On Fri, Sep 08, 2006 at 09:38:23AM +0200, c. m. wrote:
>> > i'm using the navteq data set, postgis/postgres and the uml
>> > mapserver. Actually I have created a table with forest streets and
>> > one with side streets. forest streets are a subset of side streets,
>> > i.e. a forest street is also a side street. now I want to
>> > geometrically compute the difference of the two (side - forest
>> > streets) to get an adjacent side streets table (layer)  to be able
>> > to display them properly and independently on the mapserver. as a
>> > result I always get the entire side street and not the difference
>> > between the two areas/lines...unfortunately it doesn't work and I
>> > can't understand why.
>>
>> Could you post a couple of geometries along with the difference
>> you get?
>>
>> -- 
>> Michael Fuhr
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> 
> 
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