[postgis-users] More Semantics: SRID Matching

[Martin Davis]

But then you should have tagged all your geometries with 4326 in the 
first place, no?  So then things *would* break, as required.

I'm with Paul on this - if a user hasn't taken the trouble to properly 
set the SRID, then PostGIS should just carry out the computation.  
Otherwise, you might as well insist that all geometries carry a valid 
SRID (not -1).   But being able to use -1 is useful shorthand for quick 
computation.

Paragon Corporation wrote:
> I'm afraid I agree with Jan on this.  Like Brent said you'd want to know
> about the assumption being made, but I'd just assume not have warnings and
> without warnings things like this where there is no match are just too hard
> to debug.  And code running in lalala land is not going to be looking at
> warnings.
>
> Say your table had a projection of 4326 once and then later your change it
> to 2249 or whatever and had no idea there was code lying around thinking it
> was working with 4326.  Your code would mysteriously just stop producing
> results or odd results.  
>
> I'd rather it just break than do the logically wrong thing.
>
> -1
>
> Thanks,
> Regina  
>
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Jan
> Hartmann
> Sent: Thursday, January 29, 2009 4:52 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] More Semantics: SRID Matching
>
> I wouldn't do that. My experience is that you'll run into errors that are
> very hard to detect when you allow this sort of "default" behavior. 
> What's wrong whith an extra setsrid or so?
>
> Jan
>
> Paul Ramsey wrote:
>   
>> I just did this:
>>
>> aggtest=# select name from tm_world_2 where st_dwithin(the_geom,
>> 'POINT(32.4122 -21.2178)', 0.0001);
>> ERROR:  Operation on two geometries with different SRIDs
>>
>> And you know what, that seems a bit harsh to me. Given an operation 
>> where one SRID is known (st_srid(the_geom) == 4326), and the other is 
>> unknown (-1), can we not simply assume that everything is in the known 
>> SRID?
>>
>> Comments?
>>
>> P
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-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022