Re: distance operator dont work

Dear all,

I have a table containing polygon and I try a distance operator which
fails. (select * from mytable order by point(10,10) <-> mycol)

Postgres responds that the operator <-> between a point and a polygon is
unknown.

I look in the pg_operator.h (in src/include/catalog) where I think all
builtin operators are defined and found these definitions

DATA(insert OID = 517 ( "<->" PGNSP PGUID b f 600 600 701 517
0 0 0 0 0 point_distance - - ));

DATA(insert OID = 613 ( "<->" PGNSP PGUID b f 600 628 701
0 0 0 0 0 0 dist_pl - - ));
DATA(insert OID = 614 ( "<->" PGNSP PGUID b f 600 601 701
0 0 0 0 0 0 dist_ps - - ));
DATA(insert OID = 615 ( "<->" PGNSP PGUID b f 600 603 701
0 0 0 0 0 0 dist_pb - - ));
DATA(insert OID = 616 ( "<->" PGNSP PGUID b f 601 628 701
0 0 0 0 0 0 dist_sl - - ));
DATA(insert OID = 617 ( "<->" PGNSP PGUID b f 601 603 701
0 0 0 0 0 0 dist_sb - - ));
DATA(insert OID = 618 ( "<->" PGNSP PGUID b f 600 602 701
0 0 0 0 0 0 dist_ppath - - ));

DATA(insert OID = 706 ( "<->" PGNSP PGUID b f 603 603 701 706
0 0 0 0 0 box_distance - - ));
DATA(insert OID = 707 ( "<->" PGNSP PGUID b f 602 602 701 707
0 0 0 0 0 path_distance - - ));
DATA(insert OID = 708 ( "<->" PGNSP PGUID b f 628 628 701 708
0 0 0 0 0 line_distance - - ));
DATA(insert OID = 709 ( "<->" PGNSP PGUID b f 601 601 701 709
0 0 0 0 0 lseg_distance - - ));
DATA(insert OID = 712 ( "<->" PGNSP PGUID b f 604 604 701 712
0 0 0 0 0 poly_distance - - ));

DATA(insert OID = 1522 ( "<->" PGNSP PGUID b f 600 718 701
0 0 0 0 0 0 dist_pc - - ));
DATA(insert OID = 1523 ( "<->" PGNSP PGUID b f 718 604 701
0 0 0 0 0 0 dist_cpoly - - ));
DATA(insert OID = 1520 ( "<->" PGNSP PGUID b f 718 718 701
1520 0 0 0 0 0 circle_distance - - ));
DATA(insert OID = 1524 ( "<->" PGNSP PGUID b f 628 603 701
0 0 0 0 0 0 dist_lb - - ));

and there is none between a point and a polygon. (600 604) (furthermore
the 628 type is defined in ptypes.h as not implemented.

I did the following test,
I patch the line
DATA(insert OID = 613 ( "<->" PGNSP PGUID b f 600 628 701
0 0 0 0 0 0 dist_pl - - ));

replacing 628 by 604 ,
compiling and reinstalling everything including the database
and It works (I didnt verify the result)

So I am wondering , if I miss something, do I have to convert my point
in a degenerated circle or polygon) or do you forget one definition ?

I have checked the source code in versions 7.4.2,7.4.3 , 8.1.0 & 8.1.4.

The version I patched is 8.1.4 and the lines above were extracted from 7.4.2

Thank you

Bernard SNYERS
Chief Architect
Ionic Software
bs(at)ionicsoft(dot)com

On Sat, Aug 12, 2006 at 08:52:48AM +0200, bernard snyers wrote:
> I have a table containing polygon and I try a distance operator which
> fails. (select * from mytable order by point(10,10) <-> mycol)
>
> Postgres responds that the operator <-> between a point and a polygon is
> unknown.
>
> I look in the pg_operator.h (in src/include/catalog) where I think all
> builtin operators are defined and found these definitions

Are you aware that you can query the system catalogs with SQL instead
of digging into header files? See also psql's \do command.

http://www.postgresql.org/docs/8.1/interactive/catalogs.html
http://www.postgresql.org/docs/8.1/interactive/catalog-pg-operator.html
http://www.postgresql.org/docs/8.1/interactive/app-psql.html

> and there is none between a point and a polygon. (600 604) (furthermore
> the 628 type is defined in ptypes.h as not implemented.
>
> I did the following test,
> I patch the line
> DATA(insert OID = 613 ( "<->" PGNSP PGUID b f 600 628 701
> 0 0 0 0 0 0 dist_pl - - ));
>
> replacing 628 by 604 ,
> compiling and reinstalling everything including the database

The dist_pl function expects a line argument; calling it with a
different type could cause unexpected results or even a server
crash. And are you aware that you can use CREATE OPERATOR instead
of hacking the source code and recompiling?

http://www.postgresql.org/docs/8.1/interactive/sql-createoperator.html

> and It works (I didnt verify the result)

In what sense does it work if you didn't verify the result?

> So I am wondering , if I miss something, do I have to convert my point
> in a degenerated circle or polygon) or do you forget one definition ?

I'd guess that certain features remain unimplemented due to lack
of interest; maybe one of the developers can comment on the history
of support for geometry operations. A nice thing about PostgreSQL
is that it's extensible without having to hack the source code: you
can write your own functions in PL/pgSQL or C or some other language
and create operators that call those functions. Such customizations
survive migrations via database dumps so you don't have to remember
to patch the code every time you upgrade.

If you're working with spatial data then you might want to check
out PostGIS:

http://www.postgis.org/

--
Michael Fuhr

bernard snyers <bs(at)ionicsoft(dot)com> writes:
> I patch the line
> DATA(insert OID = 613 ( "<->" PGNSP PGUID b f 600 628 701
> 0 0 0 0 0 0 dist_pl - - ));

> replacing 628 by 604 ,
> compiling and reinstalling everything including the database
> and It works (I didnt verify the result)

Obviously not. line and polygon don't have the same internal
representation, so there's no way that's going to work.

regards, tom lane