Hi Gaurav,
In principle, st_distance(geom, geom) always returns minimum distance between
two geoms and it should work for any geom type (line, polygon, point). Function
st_distance(st_centroid(geom), st_centroid(geom)) may return the distance
between centroids of geoms. Calculating minimum distance of a geom to more than
one geoms is however tricky a bit. It has been quite a long time, I developed a
simple function (below) to find two nearest markets (among several markets) to
a village location based on minimum (Euclidian) distance. You may have a look
into it to get some idea. To find the centriod on minimum distance between two
lines, you need to return a line geomtery, whereas
st_distance_spheroid(geometry, geometry, spheroid) returns distance as double
precision. You need to use a function that returns a shortest line between two
gemoetries and then you can find centroid on the shortest line e.g.
st_centroid(st_shortestline(geometry, geometry))
Regards,
Muhammad Imran
PhD Student
ITC, University of Twente
CREATE OR REPLACE FUNCTION "Burkina_Faso"."BF_NN_MARKET_CAL"() RETURNS boolean
AS'
DECLARE
i integer;
result text;
BEGIN
FOR i in (select gid from "Burkina_Faso"."BF_VILLAGE_TAGED") loop
insert into "Burkina_Faso"."BF_NN_MARKET"
select b.gid, b.village,a.gid, a.market, min(st_distance(a.the_geom,
b.the_geom))/1000
from "Burkina_Faso"."BF_MARKET" a, "Burkina_Faso"."BF_VILLAGE_TAGED" b
where b.gid=i
group by a.market, b.village, a.gid, b.gid, st_distance(a.the_geom, b.the_geom)
having st_distance(a.the_geom, b.the_geom)=(select min(st_distance(a.the_geom,
b.the_geom)))
order by st_distance(a.the_geom, b.the_geom) asc
limit 2;
end loop;
return true;
END;
' LANGUAGE plpgsql;
--- On Fri, 11/18/11, Gaurav Singh <[email protected]> wrote:
> From: Gaurav Singh <[email protected]>
> Subject: [postgis-users] min distance between two lines
> To: "[email protected]"
> <[email protected]>
> Date: Friday, November 18, 2011, 3:33 PM
> Hi All,
>
> I have two lines and I want to calculate the minimum
> distance between them and finding the centroid between those
> two lines.
> Can you help me telling of ST_Distance_Spheroid is the
> right method to calculate the minimum distance between the
> two lines.
>
> Thanks,
> Gaurav Singh
> _______________________________________________
> postgis-users mailing list
> [email protected]
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>
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