[postgis-users] MakeLine question

[Markus Schaber]

Hi, Curtis,

Curtis W. Ruck wrote:
> I have a table with gps tracks stored as points, each point being one
> data record for every second.
> 
> I am trying to write a view which generates a polyline for each track. 
> I know I need to "select MakeLine(the_geom) from track_log" but the
> postgis documentation suggests "You might want to use a subselect to
> order points before feeding them to this aggregate."
> 
> Does anyone have an example of how to do this, the postgres
> documentation doesn't show an example of using a subquery in the SELECT
> list portion of the query.

One way would be:

SELECT track_id, MakeLine(the_geom) FROM (SELECT track_id, the_geom FROM
track_log ORDER BY seconds) AS foo GROUP BY track_id;

HTH,
Markus

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

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