[postgis-users] LinearReferencing: measure vertex of linestring?

Andrés Maneiro amaneiro at icarto.es
Wed Mar 28 09:22:28 PDT 2012

Hello people,

I'm reviewing what postgis is able to do in terms of Linear Referencing. As fas 
as I could see, to calibrate a linestring there is only the method ST_AddMeasure:

So, as stated in the example, the operation will create a route like:

     SELECT ST_AsEWKT(ST_AddMeasure(
     ST_GeomFromEWKT('LINESTRING(1 0, 2 0, 4 0)'),1,4)) As ewelev;
      LINESTRINGM(1 0 1,2 0 2,4 0 4)

What I'm wondering is if somehow I could calibrate the vertex of the linestring, 
having as a result, for example, this route:

     LINESTRINGM(1 0 1,2 0 *1.7*,4 0 4)

The project I'm working on is related to road management, and it's very common 
that the ratio between a route's length and its measures is not constant. So, my 
doubt goes: is it somehow possible to create a route in postgis where the 
measure and the distance are not directly related?

(For those who know how ArcGIS "dynamic segmentation" works, what I'd like to 
achive is something similar to calibrate a route using points [1]).

Let me know if I explain myself properly.



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