[postgis-tickets] [PostGIS] #5238: ST_Area() does not always follow the winding order of coordinates in a Geography

[PostGIS]

#5238: ST_Area() does not always follow the winding order of coordinates in a
Geography
---------------------+---------------------------
 Reporter:  eldang   |      Owner:  pramsey
     Type:  defect   |     Status:  new
 Priority:  medium   |  Milestone:  PostGIS 3.3.1
Component:  postgis  |    Version:  3.2.x
 Keywords:           |
---------------------+---------------------------
 The area reported by `ST_Area()` for a Geography created from coordinates
 that span > 180 degrees of longitude falls short, with a pattern that
 suggests the polygon may be getting interpreted as going the wrong way
 around the globe.

 Repro steps:

 1. `SELECT ST_Area(ST_GeogFromText('SRID=4326;POLYGON((10 -89.9999, 180
 -89.9999, 180 89.9999, 10 89.9999, 10 -89.9999))')) / 1000000;`
 2. `SELECT ST_Area(ST_GeogFromText('SRID=4326;POLYGON((0 -89.9999, 180
 -89.9999, 180 89.9999, 0 89.9999, 0 -89.9999))')) / 1000000;`
 3. `SELECT ST_Area(ST_GeogFromText('SRID=4326;POLYGON((-10 -89.9999, 180
 -89.9999, 180 89.9999, -10 89.9999, -10 -89.9999))')) / 1000000;`

 Expected behaviour:

 1. Returns approximately 170/360 of the area of the globe in sq km
 2. Returns approximately 1/2 of the area of the globe in sq km
 3. Returns approximately 190/360 of the area of the globe in sq km

 Actual behaviour:

 1. 240864321.36968684 (as expected)
 2. 255032810.86204427 (as expected)
 3. Returns exactly the same as the first test

 I have seen this in the wild with more complex polygons, which were
 getting suspiciously low areas returned.  The above example is the
 simplest case I can reproduce it with.  I do get the same behaviour if I
 offset the polygon to avoid the antimeridian (e.g. `SELECT
 ST_Area(ST_GeogFromText('SRID=4326;POLYGON((-80 -89.9999, 90 -89.9999, 90
 89.9999, -80 89.9999, -80 -89.9999))')) / 1000000;` )

 This does not affect multipolygons as long as each individual Polygon
 component spans < 180 degrees of longitude.  As a result I do have a
 relatively straightforward workaround for my own use, of simply splitting
 polygons wider than that to calculate their area.  But it is a very
 unexpected behaviour.
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/5238>
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