[postgis-users] How does makeline work?

[Guido Lemoine]

Thanks Mark. Maybe it could be helpful it this is added to the examples in
the postgis manual. There are some other functions that use geometry 
sets (extent,
accum). There's not much else googlable about those functions.

GL


Mark Cave-Ayland wrote:

>>-----Original Message-----
>>From: postgis-users-bounces at postgis.refractions.net 
>>[mailto:postgis-users-bounces at postgis.refractions.net] On 
>>Behalf Of Guido Lemoine
>>Sent: 09 September 2005 08:57
>>To: PostGIS Users Discussion
>>Subject: Re: [postgis-users] How does makeline work?
>>
>>
>>Mark,
>>
>>Thanks for the clarification.
>>
>>I tried your suggestion, already as part of my original tests. Your 
>>version gives
>>a syntax error at the inner select statement inside makeline. 
>>If I add 
>>extra brackets
>>to make it an expression, it returns the following error.
>>
>>select astext(makeline((select gcp_geom from testset order by 
>>gcp_id))) 
>>from testset;
>>ERROR:  more than one row returned by a subquery used as an expression
>>
>>I didn't report this one, because I thought it was logical (similar 
>>error for other aggregate
>>functions). But now I am not so sure.
>>
>>Guido
>>    
>>
>
>
>Hi Guido,
>
>Sorry, I made a mistake when reading the documentation :) I've had a play on
>a real database and the following should work better:
>
>
>select astext(makeline(foo.gcp_geom)) from (select gcp_geom from testset
>order by gcp_id) AS foo;
>
>select astext(makeline(foo.gcp_geom)) from (select gcp_geom from testset
>order by gcp_id desc) AS foo;
>
> 
>Kind regards,
>
>Mark.
>
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