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

Paul Ramsey pramsey at cleverelephant.ca
Wed Mar 11 09:16:59 PDT 2009

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.


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

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