Latitude, longitude and orthodromic distance in PgSQL

orthodromic.sql

CREATE DOMAIN latlong AS point CHECK (VALUE[0] BETWEEN -90.0 AND 90.0 AND VALUE[1] BETWEEN -180 AND 180);

CREATE OR REPLACE FUNCTION orthodromic_distance(latlong, latlong) RETURNS float AS $_$
     SELECT acos(
              sin(radians($1[0])) 
            * 
              sin(radians($2[0]))
            + 
              cos(radians($1[0])) 
            * 
              cos(radians($2[0]))
            * 
              cos(radians($2[1]) 
            - 
              radians($1[1]))
            ) * 6370.0;
$_$ LANGUAGE sql IMMUTABLE;

CREATE OPERATOR <-> ( PROCEDURE = orthodromic_distance
, LEFTARG = latlong, RIGHTARG = latlong
);

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