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List:       postgis-users
Subject:    Re: [postgis-users] LinearReferencing: measure vertex of linestring?
From:       Paul Ramsey <pramsey () opengeo ! org>
Date:       2012-03-28 19:29:50
Message-ID: CACowWR35A90NUmAaY_N_MhK7hkbwRE-jx_Nrws-BfBxxFRWiaA () mail ! gmail ! com
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Create a ticket describing the calibration, that's useful info and
would be a good utility for LRS users for a future version.

P.

2012/3/28 Andr=E9s Maneiro <amaneiro@icarto.es>:
> 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:
> http://www.postgis.org/docs/ST_AddMeasure.html
>
> So, as stated in the example, the operation will create a route like:
>
> =A0 =A0SELECT ST_AsEWKT(ST_AddMeasure(
> =A0 =A0ST_GeomFromEWKT('LINESTRING(1 0, 2 0, 4 0)'),1,4)) As ewelev;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 ewelev
> =A0 =A0--------------------------------
> =A0 =A0 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:
>
> =A0 =A0LINESTRINGM(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.
>
> best,
> Andr=E9s
>
> [1]
> http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/About_calib=
rating_route_measures_using_points/00390000000t000000/
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