[postgis-users] Unexpected ST_DWithin result when using geography

satoshi satoshich at gmail.com
Sun Feb 6 23:28:11 PST 2022


This query:

  ST_Buffer('SRID=4326;LINESTRING(7.1670005 45.9968257,7.1670216
45.9969537,7.1670216 45.9971326, 7.1670484 45.9972789, 7.1671905
45.9974074, 7.1672844 45.9974801, 7.1659165 46.0005209, 7.1653103
46.0010221, 7.1652359 46.0013015)'::geography, 1.0),
  'SRID=4326;POINT(7.1672844 45.9974801)'::geography,

Returns `FALSE`. Note that the point that is passed as the second parameter
to `ST_DWithin` is part of the `LINESTRING` passed in the first parameter,
so I expect it to return `TRUE`.

When removing the first or last point from the `LINESTRING`, then it
correctly returns `TRUE`.

When using `geometry` instead of `geography` and using 0.0000105 for the
buffer (which is roughly 1 meter at that latitude), then it correctly
returns `TRUE`.

Could somebody comment on this and let me know why this would happen (if
not a bug)?

Thank you,
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