[postgis-devel] How do you obtain the line that touches a polygon?

[googling1000]

Thank you for your help.
This was exactly the problem.

Sorry for the late reply.


Paul Ramsey-3 wrote:
> 
> It's possible your line doesn't quite touch the polygon, so perhaps a
> distance filter would be better with a small tolerance.
> 
> SELECT ST_AsText(myline.the_geom)
> FROM myline,mypoly
> WHERE ST_DWithin(myline.the_geom, mypoly.the_geom, 0.001);
> 
> P.
> 
> On Thu, May 29, 2008 at 2:43 PM, googling1000 <googling1000 at yahoo.com>
> wrote:
>>
>> Hi,
>> I have one polygon, and a line lies exactly on an edge of that polygon.
>> How do I obtain that line?
>>
>> Please take a look at a picture here:
>> http://googling1000.googlepages.com/example.jpg
>> (I drew the lines using different thickness so it is easy to understand
>> where each segment ended)
>> The line segment A is touching the polygon P, and I'd like to write a
>> query
>> statement that will fetch me that line.
>>
>> I tried ST_intersects and ST_Touches, but the queries return 0 rows.
>>
>> Then, I tried && which is another intersection command?
>> This is the query statment:
>> select ST_AsText(myline.the_geom) from myline,mypoly where
>> mypoly.the_geom
>> && myline.the_geom AND mypoly.polynum = '11'
>> Note that 11 is the number associated with polygon P
>>
>> I was hoping to get only the A segment, but I got all A,B,C segments as a
>> result. why is that?
>> How do I obtain segment A?
>>
>> Help will be highly appreciated.
>> --
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>>
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