[postgis-users] Difference between ST_Union and ST_Collect

[Sandro Santilli]

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.

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