[mapserver-users] Plotting points as a line from sqlite database

[Fawcett, David (MPCA)]

ST_MAKELINE() does exist in recent versions of Spatialite.  

It doesn't appear to have made it in to the docs, but it can be seen in this example from the cookbook.  http://www.gaia-gis.it/spatialite-2.4.0-4/spatialite-cookbook/html/pp-adjacent.html

Another example is in this thread from the Spatialite list:  

http://groups.google.com/group/spatialite-users/browse_thread/thread/0020f8e907ae9226

You will likely need recent versions of both Spatialite and OGR to make it work.

David.



-----Original Message-----
From: mapserver-users-bounces at lists.osgeo.org [mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf Of Stephen Woodbridge
Sent: Wednesday, June 29, 2011 10:49 PM
To: mapserver-users at lists.osgeo.org
Subject: Re: [mapserver-users] Plotting points as a line from sqlite database

On 6/29/2011 10:13 PM, Ian Walberg wrote:
> I hope this isn't too stupid a question.
>
> Would like to display a list of positions in an sqlite database as a
> line, to show the flight path of an aircraft. The data is in the db as
> Lat, Long and point (lat, long)
>
> We can display the positions as individual dots but not as a line, I
> fear the problem is that the data is a point.
>
> As the data is being accumulated we would prefer not to create a new
> line in the database each time if possible.
>
> Any suggestions to what options we have would be appreciated.

Hi Ian,

In postgis there is an aggregrate function makeline() that you can feed 
points to. I think there may be an equivalent function in SpatiaLite.

In sqlite, you might be able to use a group_concat() something like:

select 'LINESTRING('|| group_concat(lat||' '||long, ',') ||')'
   from points;

But I think the issue will be that this is not a format that mapserver 
understands. You might be able to access this via GDAL/OGR but I'm not 
sure on that.

-Steve W
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