[postgis-users] noob question

[Steve Lefevre]

On 7/4/07, Webb Sprague <webb.sprague at gmail.com> wrote:
>
> You might want to look into the "centroid" function.  I am not sure if
> that is the best, but it is useful in general.


Sorry ! I forgot to mention the centroid function in my post.

But my main question is, what is the syntax for the centriod function when
using a lot of points? Do I use multipoint?

 UPDATE table SET coords = CENTROID(geometryfromtext(' MULTIPOINT( $lat1
$long1, $lat2 $long2, $lat3 $long3)', 4326))

?


W
>
> On 7/4/07, Steve Lefevre <lawpoop at gmail.com> wrote:
> > Hello all -
> >
> > I'm working on a database with GIS data. In my table,  I have columns
> for
> > latitude, longitude, and coordinates, which is the Postgis geometry data
> > type. What I would like to do is find the midpoint or 'average' for any
> > group of points.
> >
> > I have the latitude and longitude, and then I use this syntax to create
> the
> > coordinates column value:
> >
> > UPDATE table SET coords =  geometryfromtext('POINT( longitude latitude
> )',
> > 4326)
> >
> > ( 4326 is the projection value that I understand is useful in the United
> > States.
> >
> > So now that I have a bunch of lats, longs, and coordinates, I need to
> find
> > the center point for any group of them. I can do a select query to get
> the
> > specific records I'm looking for, and then I can have the list of
> lat&long
> > points, or the coordinate geometry. How then do I take those rows and
> create
> > an SQL st
> >
> >
> > UPDATE table SET coords = geometryfromtext(' MULTIPOINT( $lat1 $long1,
> > $lat2 $long2, $lat3 $long3)', 4326)
> >
> > Can I use the 'coords' geometry object instead?
> >
> >
> >
> > --
> > "Computers are useless. They can only give you answers"
> > -- Pablo Picasso
> > _______________________________________________
> > postgis-users mailing list
> > postgis-users at postgis.refractions.net
> > http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
>



-- 
"Computers are useless. They can only give you answers"
-- Pablo Picasso
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