ST_Area regress between 2.1.2 and 2.0.4 when using use_spheroid = false

[robe]

More funkiness with use_spheroid:

SELECT gid, ST_Area(geog, false) As sphere_area, ST_Area(geog,true) AS spheroid_area
FROM (VALUES (1, ST_GeogFromText('MULTIPOLYGON(((-71.0821 42.3036,-71.0822 42.3036,-71.082 42.3038,-71.0819 42.3037,-71.0821 42.3036)))') ),
	(2, ST_GeogFromText('MULTIPOLYGON(((-71.1261 42.2703,-71.1257 42.2703,-71.1257 42.2701,-71.126 42.2701,-71.1261 42.2702,-71.1261 42.2703)))') ) ) As g(gid, geog)  ;

In POSTGIS="2.0.4" GEOS="3.4.2-CAPI-1.8.2 r0" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.10.0, released 2013/04/24" LIBXML="2.7.8" LIBJSON="UNKNOWN" (core procs from "2.0.4" need upgrade) RASTER (raster procs from "2.0.4" need upgrade) PostgreSQL 9.2.4, compiled by Visual C++ build 1600, 32-bit

 gid |   sphere_area    |  spheroid_area
-----+------------------+------------------
   1 |  228.61314662168 | 228.977274222299
   2 | 686.203767227692 | 687.292930366744

In POSTGIS="2.1.2dev r12220" GEOS="3.4.2-CAPI-1.8.2 r0" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.10.0, released 2013/04/24" LIBXML="2.7.8" LIBJSON="UNKNOWN" RASTER PostgreSQL 9.2.4, compiled by Visual C++ build 1600, 32-bit

 gid |   sphere_area    |  spheroid_area
-----+------------------+------------------
   1 | 228.671128069666 | 228.977274222299
   2 | 686.211664392567 | 687.292930366744
(2 rows)

Note how the spheroid areas between two versions agree but the sphere areas do not. Did we change our sphere between 2.0 and 2.1?

[robe]

and to paraphrase pramsey — yes we read from spatial_ref_sys now (or at least I think that is what he said).

Given that this particular change in deviation in answer is not surprising.