[postgis-devel] Re: Btree semantic (was: [postgis-users] Strange behaviour of = operator)

Paul Ramsey pramsey at refractions.net
Thu Feb 9 08:49:13 PST 2006


Sorry, I missed what the semantic is.  Is it geometries with  
identical vertex lists and vertex orders are equal?  Or is  
directionality ignored?  Or is geometric equivalence considered  
( LINESTRING(0 0, 5 5) == LINESTRING(0 0, 3 3, 5 5) )?

For ordering, I can't think of an obviously useful system. Order on  
minx(bbox())?

On Feb 8, 2006, at 8:06 AM, strk wrote:

> [ added postgis-devel ]
>
> On Wed, Feb 08, 2006 at 02:30:41PM +0200, Steffen Macke wrote:
>>> I'm ready to reopen this, as far as current semantic is not
>>> documented in the manual.
>>
>> Well, I think having an easy and intuitive way to check for duplicate
>> geometries is something great. Thus if
>>
>> select count(distinct the_geom) from test;
>>
>> and
>>
>> select the_geom,count(*) from test group by the_geom;
>>
>> work like they do after the changes mentioned in this thread,
>> PostGIS becomes a more powerful tool.
>
> Sounds fair. What about order by ? Is area a nice one for it ?
> Paul, what do you think ?
>
> --strk;




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