[postgis-users] TR: strange behavior of ST_Area(geography)

[Mike Toews]

On 16 October 2017 at 02:07, IIDA Tetsushi <hogeman at gmail.com> wrote:
> sorry, i forgot to describe my environment.
> ----------------------------------------------------------------
>  PostgreSQL 9.6.3 on x86_64-pc-linux-gnu, compiled by gcc (Debian
> 4.9.2-10) 4.9.2, 64-bit
>  POSTGIS="2.3.2 r15302" GEOS="3.4.2-CAPI-1.8.2 r3921" PROJ="Rel.
> 4.8.0, 6 March 2012" GDAL="GDAL 1.10.1,
>  released 2013/08/26" LIBXML="2.9.1" LIBJSON="0.11.99" RASTER

For PROJ versions prior to 4.9.0, the PostGIS algorithms are not
robust for geographic area calculations, so I'm not surprised to see
these results.

PROJ 4.9.0 and later includes GeographicLib's C functions, which are
used by PostGIS to calculate area on an ellipsoid of revolution. It's
been robust and reliable, so far.