[postgis-users] Need some help with storing line segments

[Stephen Woodbridge]

I'm not sure you can do this in postGIS, but the idea would be to try 
something like:

Table points: pid, point_geom, attributes, ...
Table lines: pid_from, pid_to, attributes, ...
View: select makeline(
          (select point_geom from points a, lines b where 
a.pid=b.pid_from) as p1),
          (select point_geom from points a, lines b where 
a.pid=b.pid_to) as p2)) as line_geom, attributes from lines;

If the view trick doesn't work then you might want to add the line_geom 
directly to the lines table and use a trigger on the points table to 
update the line_geom if the points_geom gets changes based on the pid field.

-Steve


Ehud Shabtai wrote:
> Hi,
> 
> I'm new to postgis and this is my first usage of it. I read the
> documentation, but I could not find a way to store the data I want (in
> the way I want it).
> 
> Here's the story:
> 
> I got some GPS tracks which I want to store in postgis. Before I store
> them, I do some processing and build line segments from the separated
> GPS points. Now, I'd like to store these lines in postgis, but I'd
> also like to keep attributes for each node of the line (node id, time,
> direction for next node, etc').
> 
> The only way I see it is to store each point twice, first as a point
> with some attributes and then as a line. The problem with this
> approach is that I'd like to be able to update the coordinates of a
> specific point, which will result in searching for the line consisting
> this point and then updating the line.
> 
> Is there any better approach to sore my data?
> Can I update a specific point of a line in postgis, or the only way is
> to get all the points of a line and create a new one?
> 
> Thanks,
> 
> Ehud.
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