Hi:
I'm surprised at the discrepancy of area calculations from this query:
---------------
WITH shapes as (
select 1 as rownum, ST_GeogFromText('POLYGON((-144 -63,-144 -54,-126 -54,-126
-63,-144 -63))') as shape
union
select 2 as rownum, ST_GeogFromText('POLYGON((-90 -63,-90 -54,-72 -54,-72
-63,-90 -63))') as shape
)
select rownum, ST_Area(shape) as spheroid, ST_Area(shape, false) as sphere,
ST_Area(shape) - ST_Area(shape, false) as delta
from shapes;
---------------
which returns
rownum | spheroid | sphere | delta
--------+------------------+------------------+------------------
1 | 1040833443426.88 | 170313180619.486 | 870520262807.394
2 | 1040833443426.88 | 1035406049943.11 | 5427393483.77466
(2 rows)
Both polygons should cover the same area on the globe - they're at the same
latitude but shifted longitudinally. As expected, the spheroidal area is the
same for both polygons, but the spherical area is *quite* different. The
polygons don't touch any of the obvious edge cases like the poles, equator, or
longitude 0 or 180.
Can someone explain this to me? Is this an expected result?
Best,
Pete Clark
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