# [postgis-users] distance from centroid to the points that form the outer boundary of the polygon

Tom van Tilburg tom.van.tilburg at gmail.com
Mon Jul 30 13:05:23 PDT 2012

```Hi Yamini,

Are you sure that multipolygons is what you want to work with? Since a
multipolygon can consist of multiple polygons (obviously) who share a
common centroid that can be way outside your actual polygons.

That said, I would make use of ST_Dumppoints to do that.
Something like:
============
WITH pointsdump AS
(
SELECT gid, ST_Centroid(geom) AS centre, (ST_Dumppoints(geom)).geom
AS point FROM polygontable
)

SELECT gid, ST_Distance(centre, point) AS distance FROM pointsdump
===========

Now for every point in a geometry with a known gid you will see the
distance to it's centroid.
You can do statistics on these numbers with something like:
SELECT gid, avg(distance) avg, max(distance) max, etc... FROM
results GROUP BY gid

Cheers,
Tom

On 30-7-2012 15:04, Yamini Singh wrote:
>
> Hi All,
>
> I am looking for suggestions for the following problem I have at hand.
>
> 1.I have a table that contain multipolygons
>
> 2.I want to calculate the maximum distance of points that form the
> polygon  from the centroid of the polygon. For example of the polygon
> is formed of 50 points then I want to have distance of all the 50
> points from the centroid of the polygon.
>
> I am not sure if someone has done this before. But I am finding it
> difficult to implement it. Any help in this regards is welcome...
>
>
> Best,
>
> YJS
>
>
>
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> postgis-users at postgis.refractions.net
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