[postgis-users] RE: postgis-users] a line' s direction

[Hartmut Tschauner]

Ahmet,

You would use a query like the following, which returns the azimuth from the
start point to the end point of a simple line(string):

SELECT azimuth(pointn(the_geom, 1), 
pointn(the_geom, npoints(the_geom))) as azimuth
FROM rivers;

If you need to deal with multi geometries, it would get a bit more
complicated. For example, the azimuth from the start point to the end point
of the first geometry:

SELECT azimuth(pointn(geometryn(the_geom, 1), 1), 
pointn(geometryn(the_geom, 1), npoints(the_geom))) as azimuth
FROM rivers;

Cheers,
Hartmut

Hartmut Tschauner
Department of Archaeology
Seoul National University
Gwanak-Gu Sillim 9-dong San 56-1
Seoul, 151-742
Korea
ph. +82 (2) 880-9260


>thank you for your help about line direction. I tested: bzk=> select
astext(wkb_geometry) from bartin_fay limit 1; astext
>-----------------------------------------------------------
LINESTRING(458329.385 4604735.295,458326.082 4604735.287) (1 row) bzk=>
select public.azimuth('point(458329.385 4604735.295)', 'point(458326.082
4604735.287)'); azimuth ------------------ 269.861227562345 (1 row)
>~~~~~~~~~~~~~~~~~~ which function can I use to get end points of lines to
input function ? I have a huge dataset containing linestring geometric data.
kind regards 

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