[postgis-users] Line To Path

[George Silva]

In the same trailing of that question and the answer, that select statement
would run the function st_union in that table, without the need to create a
new table or geometry column?

Sorry to use this post for this, just tought its a quite novice question, so
more people could use the answer.

Thx

Att.

George

On Wed, Apr 30, 2008 at 7:20 PM, Paragon Corporation <lr at pcorp.us> wrote:

> Bob,
>
> If I understand you correctly, I think you want to use one of the
> following
>
> SELECT somefield, ST_Union(the_geom)
> FROM sometable
> GROUP BY somefield
>
> So lets say you want to collapse 3 rows into 1 then you just need to group
> by some common field.
>
> E.g. if somefield = 1 for your 3 records, then those would get rolled into
> the same record.
>
> The above will give you a LINESTRING or MULTILINESTRING.  If you have all
> LINESTRINGS, then may be more efficient to do this.  The below will first
> collapse all with common somefield into a MULTILINESTRING and then the
> LineMerge will do the best it can to stitch back into a single line
> string.
> This is not possible with completely disjoint linestrings.
>
> SELECT somefield, ST_LineMerge(ST_Collect(the_geom))
> FROM sometable
> GROUP BY somefield
>
>
> If you are using the older version of Postgis, you can just take out the
> ST_
> in the examples I have above.
>
> Hope that helps,
> Regina
>
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob
> Pawley
> Sent: Wednesday, April 30, 2008 12:40 PM
> To: PostGIS Users Discussion
> Subject: [postgis-users] Line To Path
>
> Is there a method of converting three lines that require three rows into a
> path that occupies a single row??
>
> Bob Pawley
>
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