This might do what you want:
select st_distance_spheroid(a.the_geom, b.the_geom, 'SPHEROID["WGS
84",6378137,298.257223563]') as minimum,
st_distance_spheroid(st_centroid(a.the_geom),
st_centroid(b.the_geom), 'SPHEROID["WGS 84",6378137,298.257223563]') as
centroid
from lines a, lines b
where a.gid=<gid_a> and b.gid=<gid_b>
-Steve
On 11/20/2011 4:47 PM, muhammad imran wrote:
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
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