[mapserver-users] Extracting X,Y from MULTIPOINT data

[Suman Chatterjee]

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




-----Original Message-----
From: Andy Colson [mailto:andy at squeakycode.net] 
Sent: Monday, August 10, 2009 8:52 AM
To: Suman Chatterjee
Cc: mapserver-users at lists.osgeo.org
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

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