[postgis-users] MULTIPOINT geometry variable

[Markus Schaber]

Hi, Rodrigo,

"Rodrigo Martín LÓPEZ GREGORIO" <rodrigomlg at yahoo.com.ar> wrote:

> But if mymultipoint variable has not points yet, this doesnt work so I must
> check in every assignment if mymultipoint variable is null or empty or
> something like that.

Yes, but you can use an SQL-Level CASE expression to simplify that:

mymultipoint:=CASE WHEN mymultipoint IS NULL THEN newpoint ELSE
GeomUnion(newpoint, mymultipoint) END;

Or even shorter, using COALESCE:

mymultipoint:=COALESCE(GeomUnion(newpoint, mymultipoint), newpoint);

or:

mymultipoint:=GeomUnion(newpoint, COALESCE(mymultipoint, newpoint));

> However I think that there may be a much simple way to do that.

In case you find one, please tell me.

> I think that must be something like
> addpoint(mymultipoint,newpoint).

But for your solution, you also need some notion of an "empty
multipoint" to start with, so that won't change your problem.

> Another solution could be initialize mymultipoint variable in some way that
> not implies adding a point.

Initially, I thougt you could initialize your multipoint variable with
an empty geometry collection, but it seems that geomunion does not
support geometry collections as input argument, which is braindead
IMHO, and I think patches fixing that will be accepted.




Regards,
Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

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