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

[Kevin Neufeld]

Try moving your query into a subquery and then taking the max distance.  Also, you can probably drop the subquery you 
put as a parameter to the generate_series call.  Why are you converting the geometry to text, then back to a geometry again?

ie.
SELECT "cellID", max(dist)
FROM (
   -- Your query here, but also select the cellID to group on
   SELECT
     cellID,
     distance_spheroid(
        geometry_centroid,
        ST_PointN(
          ExteriorRing(geometry_zone),
          generate_series(1, ST_NPoints(geometry_zone))
        ),
        'SPHEROID["WGS 84",6378137,298.257223563]'
      ) AS dist
   FROM "208_1_26624_zones"
   WHERE > "cellID"='1'
) AS foo
GROUP BY "cellID";

-- Kevin

My Pid wrote:
> 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 <mailto: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.
> 
>     thanks in advance for your help !
> 
>     regards,
>     Nick
> 
> 
> 
> 
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