[postgis-users] GeomUnion() as aggregate

[Markus Schaber]

Hi, Michael,

Michael Fecht schrieb:
> GeomUnion() as aggregate to union linestrings returns  a multilinestring
> with lineparts in the reverse order than the original linestrings.
> [...]
> This behaviour of the GeomUnion() Funktion is not intuitive. Maybe the
> processing order should be adapted.

Apart from putting additional burden on the algorithm, this is
technically impossible for arbitrary input

Imagine the following input data:

LINESTRING(0 0, 1 1, 1 2);
LINESTRING(3 3, 1 2, 1 1);

Which is the order you want the (1 1, 1 2) part to be output?

LINESTRING(0 0, 1 1, 1 2, 3 3) or LINESTRING(3 3, 1 2, 1 1, 0 0)?

Markus