[postgis-users] st_astext() created invalid

[Paul Ramsey]

You've got a visible example of why the canonical format of PostGIS is
hexwbk, and not wkt, as it was in the 0.x versions. The human readable
output is not quite exactly the same as the binary representation.
Since your geometry is just a hair's breadth from being invalid, maybe you
should just accept some invalidity work: round your geometry to a tolerance
with ST_SnapToGrid and then run ST_MakeValid on them to reform them into a
more valid structure.
P.

On Thu, Jul 21, 2016 at 8:04 AM, Brian Peschel <brianp at occinc.com> wrote:

> Not sure I understand what is happening here.
>
> I have a geom:
> select * from my_temp ;
>
> geom
>
>
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
>  0103000020AD100000010000000B0000006D514CC326AC57C029776BF2CF214440B742588D25AC57C0D7F84CF6CF2144406E514CC326AC57C029776BF2CF21444015CCF33B28AC57C084FAF1F2CF2144405748540328AC57C096010C70E621444090EC5BF720AC57C0D8C2876DE62144409C3B551921AC57C0AFFE19EFD8214440F555A82421AC57C0043D2F70D42144401508BE2F21AC57C07110D308D02144404E70FB2F21AC57C0C5BB6DF0CF2144406D514CC326AC57C029776BF2CF214440
>
> Which PostGIS says is valid:
> select st_isvalid(geom) from my_temp ;
>  st_isvalid
> ------------
>  t
> (1 row)
>
> I then convert to a format I can read:
> select st_astext(geom) from my_temp ;
>
> st_astext
>
>
> -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>  POLYGON((-94.6898658986372 40.2641585373625,-94.689792 40.264159,-94.6898658986372
> 40.2641585373625,-94.6899557 40.2641586,-94.6899422
> 40.2648449,-94.6895121 40.2648446,-94.6895202 40.2644328,-94.6895229
> 40.2642956,-94.6895255428102 40.2641612082088,-94.6895256
> 40.2641583,-94.6898658986372 40.2641585373625))
> (1 row)
>
> But that isn't valid.  It is self intersecting (point 1 and point 3
> repeat).  And if I check the validity of the st_astext version:
> select st_isvalid(geom), st_isvalid(st_geomfromtext(st_astext(geom),
> 4269)) from my_temp;
> NOTICE:  Self-intersection at or near point -94.689865898637194
> 40.264158537362498
>  st_isvalid | st_isvalid
> ------------+------------
>  t          | f
> (1 row)
>
> Any idea what is going on here and how can I prevent it?
>
> TIA!
> - brian
>
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