# [postgis-users] Re: maximum distance between a POINT and POLYGON

My Pid mamat750 at gmail.com
Thu Feb 19 04:14:25 PST 2009

```Hello again,

I found the generate_series function (yes i am a newbie!) and I can use it
in order to calculate the distance between
my centroid (geometry_centroid) and my polygon (geometry_zone) with the
following request

SELECT
(distance_spheroid(geometry_centroid,ST_AsText(ST_PointN(ExteriorRing(geometry_zone),
generate_series(1,(SELECT npoints(geometry_zone) FROM "208_1_26624_zones"
WHERE "cellID"='1')))), 'SPHEROID["WGS 84",6378137,298.257223563]')) as d
FROM "208_1_26624_zones" WHERE "cellID"='1';

Now I can't use the max function because of the following error: "set-valued
function called in context that cannot accept a set"
when I use

SELECT
max(distance_spheroid(geometry_centroid,ST_AsText(ST_PointN(ExteriorRing(geometry_zone),
generate_series(1,(SELECT npoints(geometry_zone) FROM "208_1_26624_zones"
WHERE "cellID"='1')))), 'SPHEROID["WGS 84",6378137,298.257223563]')) as d
FROM "208_1_26624_zones" WHERE "cellID"='1';

any idea ?

thanks!
Nick

2009/2/18 My Pid <mamat750 at gmail.com>

> Hello,
>
> I would like to know how I could get the maximum distance between a POINT
> and a POLYGON.
> (the POINT i am talking about here is in fact the ST_Centroid of the
> mentionned POLYGON)
>
> I looked for a function that transform my POLYGON into several POINT but
> without success.
>
> I am working with longitude, latitude, altitude for POINT
> It is really the max distance that I am looking for (not the minimum
> distance.)
> and "accuracy" is important to me.
>