[postgis-users] Project points over a line

Rodrigo Martín LÓPEZ GREGORIO rodrigomlg at gmail.com
Thu Jul 5 08:35:02 PDT 2007

Hi Gus.

If what you want is get the nearest point of a linestring to a point you
should use:


where the geom is the network link linestring and yourpoint is your point

However this is the nearest point from the linestring to your point and I'm
not sure if this is what you want (because the "orthogonal projection" could
be outside the network link if I'm not wrong)

Also I'm not sure if you want to add that point as a vertex in your network
link or just want to get the position of that point.

Obviously you must do the necesary joins in the query so the function will
use the right "the_geom" (i.e. the linestring of the related network link).

I hope it helps. If you have any question ask me again.


On 7/5/07, Gustavo Ces <g.ces at pettra.es> wrote:
>  Hi all,
>     I´m trying to assing some polygon centroids to a network. I´ve got the
> network and those centroids has as atribute a link_id. The question is, is
> it posible to make an orthogonal projection over its relationated network
> link? What i want is to add a node into the link with the shortest distance
> between them. Something like this
>                            I
>         O--------------> I
>                             I  network link
>  centroid                I
> Thanks in advance! ( ya, i know, not a great schema!) :)
> Gus
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