[postgis-users] postgis function

[Frank Koormann]

* Valtz Com <valtz_com at hotmail.com> [070503 14:23]:
> Hi all,
> can someone give me a hint for one problem...
> 
> i have a linestring. it has start point coordinates, end point coordinates 
> and of course length and each point has (x,y) coordinates pair. these x,y 
> coordinates are stored in a separete table for every start and end point 
> respectively . let suppose that length of linestring is 500 meter. i am at 
> 300 meter away from end point of line string. i want to get my position in 
> (x,y) coordinates on this line string. any hint......

Have a look at Linear Referencing

http://postgis.refractions.net/docs/ch06.html#id2898867

        line_interpolate_point(linestring, location)

        Returns a point interpolated along a line. First argument must be a
        LINESTRING. Second argument is a float8 between 0 and 1 representing
        fraction of total 2d length the point has to be located.

HTH,

        Frank

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