operator @@ is not supported by path; doc says otherwise
Hello,
The documentation for 13 and 14 says in "Geometric Functions and
Operators" https://www.postgresql.org/docs/14/functions-geometry.html:
@@ geometric_type → point
Computes the center point. Available for box, lseg, path, polygon,
circle.
@@ box '(2,2),(0,0)' → (1,1)
However, apparently, this operator does not work for path:
$ psql
psql (14.1)
Type "help" for help.postgres=# SELECT @@ path '[(0,0),(0,1)]';
ERROR: function "path_center" not implemented
postgres=#
Same for a closed path:
postgres=# SELECT @@ path '((0,0),(0,1))';
ERROR: function "path_center" not implemented
Quick tests show that other types listed (box, lseg, polygon, circle)
are supported, so only the path is extra.
This sentence in the documentation came from 791090bd775b (REL_13_STABLE
and later). What slightly confuses me is that path_center has been
listed in src/include/catalog/pg_operator.dat and pg_proc.dat (and
pg_operator.h/pg_proc.h before that) since 3c2d74d2a (1997!), but since
a3d284485 (2018) we have a regression test ensuring that "function
"path_center" not implemented".
The easiest fix is, obviously, removing 'path' from the list in the
documentation. Or, if that would be an actual improvement, I could
submit a patch to support a path_center as well. Not sure if there is
any actual need for that, though: I found this by just goofing around,
not because I actually needed to calculate the center for some path.
Also, converting to polygon might be a workaround for those who might
need that feature. Please let me know if implementing path_center would
be a useful addition.
P.S. I've sent a report though a submit web form on a documentation web
site two days ago, but, apparently, that email was not delivered to this
list.
Anton Voloshin
Postgres Professional, The Russian Postgres Company
https://postgrespro.ru
Anton Voloshin <a.voloshin@postgrespro.ru> writes:
The documentation for 13 and 14 says in "Geometric Functions and
Operators" https://www.postgresql.org/docs/14/functions-geometry.html:@@ geometric_type → point Computes the center point. Available for box, lseg, path, polygon, circle. @@ box '(2,2),(0,0)' → (1,1)
However, apparently, this operator does not work for path:
postgres=# SELECT @@ path '[(0,0),(0,1)]';
ERROR: function "path_center" not implemented
The fact that this operator is documented is probably my fault
--- when I went through the operator tables not long ago,
I made sure there was an entry for every operator listed in
the system catalogs. It didn't enter my mind that some of
them might be pointing at useless stubs :-(.Looking through geo_ops.c, I see that not only path_center
but also dist_lb, dist_bl, close_sl, close_lb, poly_distance
error out with "not implemented".
Given that that code has sat there for more than 20 years
with nobody coming to finish the job, I think we should
just rip those functions and catalog entries out altogether.
It's misleading and probably a small waste of cycles to
have useless entries in pg_proc and pg_operator.
regards, tom lane