-----Original Message-----
From: Andy Colson [mailto:[email protected]]
Sent: Monday, August 10, 2009 8:52 AM
To: Suman Chatterjee
Cc: [email protected]
Subject: Re: [mapserver-users] Extracting X,Y from MULTIPOINT data
Suman Chatterjee wrote:
Hi all,
I have some multipoint data in postgis that I got from street
intersections. But I am not able to extract the X,Y coordinates from
the
MULTIPOINT data.
Is there any function in postgis by which I can extract the X,Y point
data from them?
Please help!
Thanks,
Suman
Yes. Are you looking for all points? Just the first? Some subset?
How do you want to see it?
Did you try ST_AsText(col)?
There is also ST_NumPoints(geometry) and ST_PointN(geometry,integer) if
you want to look at them individually. An example of what youd like to
see, or what you are trying to do might be helpful.
More functions here:
http://postgis.refractions.net/documentation/manual-1.3/ch06.html
-Andy
Suman Chatterjee wrote:
> Hi Andy,
> Thanks for your help. Actually, I am having both point and multipoint
> data in the same table which I got through road intersections by
> applying ST_intersection.
> I am using this function for extracting the coordinates from the POINT
> data.
>
> Select distinct
> x(geometryn(multi((st_intersection)),1)),y(geometryn(multi((st_intersect
> ion)),1)),c,d from (select
> ST_intersection(a.the_geom,b.the_geom),a.fname as c,b.fname as d from
> roads1 as a, roads1 as b where a.fname<>b.fname and
> ST_intersects(a.the_geom,b.the_geom) as drfe
>
> But I am not getting the X,Y for the multipoint data. I require X,Y for
> all the points within the multipoint set.
> I can extract the multipoints from the whole by
>
> Create table ex_intersects as (select
> ST_intersection(a.the_geom,b.the_geom),a.fname as c,b.fname as d from
> roads1 as a, roads1 as b where a.fname<>b.fname and
> ST_intersects(a.the_geom,b.the_geom)
>
> Select st_intersection from ex_intersects where
> geometrytype(ST_intersection)='MULTIPOINT'
>
> I tried with St_astext but it is giving the set of multipoints. But I
> want the X,Y for all the points within the multipoint geometry.
>
> How to do that?
> Thanks
> Suman
>
Wow, you are a lot deeper into postgis than I am, not sure if I'll be
any help.
Question: ST_intersection(a.the_geom,b.the_geom) returns a multipoint?
Then x(geometryn(multi((st_intersection)),1)) would return just the x
coord of the first point?
but you want the x coord of all the points? (yes, y too, I'm just
trying to break it down to understand)
-Andy
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