[postgis-users] How to extract common linestring of polyon and linestring

[Paul Ramsey]

Extract the exterior ring of your political boundaries, so you're  
working with linestrings.
Then see which rivers have start and end segments very close to those  
boundaries. Should be  a start.

P

On Mar 11, 2009, at 8:49 AM, akrherz at iastate.edu wrote:

> Greetings,
>
> Firstly, PostGIS continues to rock!  Thanks so much for this  
> software...
>
> My question is that I have a rivers linestring table and a political  
> boundaries table (US counties) polygon.  I am wishing to extract the  
> portion of the river geometry that lies along a county border.  Of  
> course, these two layers don't have the same individual point  
> precision, so I suspect some buffering, simplification is  
> necessary.  I am not seeking anything exact, but something like if  
> the river and a county border are within a few hundred meters of  
> each other for some distance along the river and county border.
>
> I can't seem to figure out which functions could accomplish this  
> task, or if it is possible. Currently, I have no issue finding  
> points of intersection, so perhaps that is part of the solution that  
> is staring me in the face :)
>
> Thanks!
>  daryl
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--
Paul Ramsey
pramsey at cleverelephant.ca
+1 250 885 0632