[postgis-users] Difference between ST_Union and ST_Collect

[Luca Morandini]

On 05/25/2012 08:41 PM, Sandro Santilli wrote:
> On Fri, May 25, 2012 at 08:38:44PM +1000, Luca Morandini wrote:
>
>> The issue has been solved by using ST_Union, but I still can't
>> fathom why entire polygons were dropped by ST_BuildArea when their
>> boundaries intersected..
>
> ST_BuildArea expects input to be correctly noded. Failing that, the
> actual result is undefined. Passing the input trough ST_Union is a trick
> to obtain proper noding.

Crystal clear :)

Regards,

Luca Morandini
Data Architect - AURIN project
Department of Computing and Information Systems
University of Melbourne