calculating distances using geographies

[Foley, Peter (RIS-DBN)]

Hi,

Following a recent upgrade from postgresql 10 / postgis 2.5.3 to posgresql 15.0 / postgis 3.4.2, we  have noticed that distances calculated using geography types appear to return incorrect results in the new version. postgresql 10 / postgis 2.5.3 returns the correct results.

For example, the following wgs84 polygons are 1.65m apart but st_distance and st_dwithin report them as 0m apart when casting them to geographies

select st_distance(st_geometryfromtext('POLYGON ((-1.7485534738529238 52.477989324720184, -1.7485528426344397 52.47797089391474, -1.748563887653701 52.47797046786393, -1.7485727216213993 52.47797048661752, -1.7485733502887397 52.47798936691661, -1.7485739840754728 52.478007348228196, -1.748563677771212 52.47800732634904, -1.7485541076315525 52.47800730603188, -1.7485534738529238 52.477989324720184))',4326)::geography,st_geometryfromtext('POLYGON ((-1.748665164272404 52.47789651546308, -1.748705653223533 52.477896601376905, -1.7487057222918938 52.47788446504611, -1.7487307518185344 52.47788451814952, -1.7487299491521497 52.47789620342481, -1.7487660211267058 52.477896279947124, -1.748767153309673 52.477956065736684, -1.7486648265496951 52.477955848635304, -1.7485639721184771 52.477955634571074, -1.7484653236191374 52.47795587460495, -1.748465659049668 52.47789699092737, -1.7485017310241382 52.477897067530265, -1.7485018001486063 52.47788493119968, -1.7485297717654242 52.47788544009214, -1.7485297103282949 52.477896227941585, -1.748562835091827 52.47789674776739, -1.7485996432291142 52.47789682590328, -1.7485997123266428 52.47788468957258, -1.7486276865033974 52.47788474894817, -1.748627619972449 52.477896435785155, -1.748665164272404 52.47789651546308))',4326)::geography,true)

st_distancespheroid using the geometries returns the correct distance:

select st_distancespheroid(st_geometryfromtext('POLYGON ((-1.7485534738529238 52.477989324720184, -1.7485528426344397 52.47797089391474, -1.748563887653701 52.47797046786393, -1.7485727216213993 52.47797048661752, -1.7485733502887397 52.47798936691661, -1.7485739840754728 52.478007348228196, -1.748563677771212 52.47800732634904, -1.7485541076315525 52.47800730603188, -1.7485534738529238 52.477989324720184))',4326),st_geometryfromtext('POLYGON ((-1.748665164272404 52.47789651546308, -1.748705653223533 52.477896601376905, -1.7487057222918938 52.47788446504611, -1.7487307518185344 52.47788451814952, -1.7487299491521497 52.47789620342481, -1.7487660211267058 52.477896279947124, -1.748767153309673 52.477956065736684, -1.7486648265496951 52.477955848635304, -1.7485639721184771 52.477955634571074, -1.7484653236191374 52.47795587460495, -1.748465659049668 52.47789699092737, -1.7485017310241382 52.477897067530265, -1.7485018001486063 52.47788493119968, -1.7485297717654242 52.47788544009214, -1.7485297103282949 52.477896227941585, -1.748562835091827 52.47789674776739, -1.7485996432291142 52.47789682590328, -1.7485997123266428 52.47788468957258, -1.7486276865033974 52.47788474894817, -1.748627619972449 52.477896435785155, -1.748665164272404 52.47789651546308))',4326))

Has anyone noticed this issue before? It occurs to me that there may be a configuration option that we need to set when installing postgis.

Many thanks,


Peter Foley

Senior Data Scientist II

++353 1 247 1527 Direct

peter.foley at lexisnexisrisk.com<mailto:peter.foley at lexisnexisrisk.com>

[cid:764600d2-550f-41fa-a0df-f611a45270f2]<https://risk.lexisnexis.com/>



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