[postgis-users] Postgis - Line to Point distance

[Peter Kukuča]

Hi Pedro,

thank you for your reply.

I cannot use pointn, the line can be up to several hundred kilometers long
and consits of up to 800 points, so this would be too rough.

Regardinf the decond suggestion, that is exactly what I am doing now, but I
don't know, which projection (srid) to transform the wgs84 data into. It
should work on all of the earth's surface, at least in all of europe for a
start. And from what I found, the projections are usually tied to a small
territory. I was thinking about mercator projection, but there is a zillion
of them in postgis. And I found a post, that the one with srid 900913 is
working great, but I don't have that one in my postgis.

2009/7/10 Pedro Doria Meunier <pdoria at netmadeira.com>

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> Hi Peter
>
> You could use the pointn(geometry, n) for the first point of the
> linestring as a first approach.
> As far as meters are concerned here's a little example of transforming
> the geometry to the desired projected system:
>
> select distance(transform(u.coordinates,srid),
> transform(p.geometry,srid)) AS thedistance
>
> HTH,
>
> Pedro Doria Meunier
> GSM: +351 96 17 20 188
> Skype: pdoriam
>
>
>
>
> Peter Kukuča wrote:
> > Dear sir,
> >
> > I am not sure if I am writing to the correct email address. I have
> > found a post on the postgis-users formu from *Rich Gibson *and this
> > address was next to it.
> >
> > I am using postgis for a while now and it is great. It solved a lot
> > of problems for me.
> >
> > However, I am now facing a problem I cannot solve. I searched for
> > almost two days now, but I still cannot find an answer. Here is my
> > problem:
> >
> > I have a database of linestrings in wgs84 projection and points in
> > wgs84 projection. I would like to determine the distance between a
> > line and a point. The ST_distance function does this very well, but
> > it does not take the wgs84 projection into account and also, the
> > result is in degrees. On the other hand, the ST_Distance_Spheroid
> > does take the wgs84 into accound and does give the result in meters,
> > but it does not accept a linestring as an input parameter.
> >
> > Is there any way i can the distance between a line and a point in
> > meters from the wgs84 projected input? I do not need grat accuracy.
> > +-5 meters is still good enough. Thank you for your tips.
> >
> > --
> > S pozdravom (regards)
> > Ing. Peter Kukuča
> >
> > ----------------------------------------------------------------------
> >
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-- 
S pozdravom (regards)
Ing. Peter Kukuča
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