I am trying to create a great circle line in order to ascertain if one was looking 'straight-out' from the end of a pier what country/place they would be viewing. I have the below PostGIS code written:
-- assume two points, calculate the angle, then extend it. -- point 1 = -33.6307920509579, 115.338797474435 -- point 2 = -33.6290969607648, 115.338316140276 SELECT ST_Segmentize( -- break it up into segments so it looks better when re-projecting for display ST_MakeLine( ST_SetSRID(ST_Point(115.338797474435, -33.6307920509579), 4326) -- starting point (ST_MakeLine expects projected coordinates) ,ST_Transform( ST_Project( -- find a point a long way away to use as the second point in the line ST_Point(115.338797474435, -33.6307920509579)::geography -- starting point again ,20000000 -- 1/2 circumference of earth at the equator (should get us far enough) ,ST_Azimuth(ST_Point(115.338797474435, -33.6307920509579)::geography, ST_Point(115.338316140276, -33.6290969607648)::geography) -- angle between my two points )::geometry, 4326) )::geography ,20000 -- break it into segments of 20km );
When I create the linestring and open it in QGIS I get a great circle line but the angle is not correct (as shown below). What am I missing?