Hello,

I am trying to verify the distance calculation (using geographies and use_spheroid=true) between a line and a point.

I
have used GeographicLib to generate a geodesic (using the wgs84
ellipsoid) between points 0 0 and 10 50 (lng lat). I generate a point
lies on the edge (at the mid point) which is 3.91451185 25.11977359.
When I use st_distance to compute the distance between the edge and the
point I expect the answer to be close to 0. But it is not.

select st_distance(st_geogfromtext('SRID=4326;point( 3.91451185 25.11977359 )'),st_geogfromtext('SRID=4326;linestring(0.00000000 0.00000000, 10 50 )'), true);

produces: 274.54332271 meters. If I use use_spheroid=false the answer is 274.10911308.

Is
this because the distance calculation between a point and a line is
done by projecting the point to the line assuming a perfect sphere? Or
am I doing something wrong?

I am using Postgresql-9.5 and PostGIS-2.2 on Ubuntu 16.04.

Thanks

--

Hector

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