[postgis-users] Postgis - Line to Point distance

Fri Jul 10 02:23:19 PDT 2009

How is your query calculating the distance between a point and a line? Are
you not just calculating the length of the line?

2009/7/10 Pavel Iacovlev <iacovlev.pavel at gmail.com>

> Works on lines for me:
>
> QUERY:
> select ST_length_spheroid(st_transform(the_geom, 4326),
> 'SPHEROID["GRS_1980",6378137,298.257222101]') as ellps_distance,
> st_distance(the_geom) as normal_distance from fondcart_layers.roads
> limit 1
>
> RESULT:
> ellps_distance: 9214.65310341668
> normal_distance: 9214.10811677981
>
> 2009/7/10 Peter Kukuča <pjr.kukuca at gmail.com>:
> > ST_Length_spheroid is perfectly great, but it does not take a line as an
> > input :-(
> >
> > 2009/7/10 Pavel Iacovlev <iacovlev.pavel at gmail.com>
> >>
> >> And for geometry length use ST_length_spheroid(geometry,spheroid)
> >>
> >> On Fri, Jul 10, 2009 at 11:48 AM, Pavel
> >> Iacovlev<iacovlev.pavel at gmail.com> wrote:
> >> > you can take the middle of the line,
> st_line_interpolate_point(the_geom,
> >> > 0.5)
> >> >
> >> > 2009/7/10 Peter Kukuča <pjr.kukuca at gmail.com>:
> >> >> 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>
> >> >>>
> >> >>> -----BEGIN PGP SIGNED MESSAGE-----
> >> >>> Hash: SHA1
> >> >>>
> >> >>> 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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> >> >>> _______________________________________________
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> >> >>
> >> >>
> >> >>
> >> >> --
> >> >> S pozdravom (regards)
> >> >> Ing. Peter Kukuča
> >> >>
> >> >> _______________________________________________
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> >> >>
> >> >>
> >> >
> >> >
> >> >
> >> > --
> >> > http://iap.md, The future is open
> >> >
> >>
> >>
> >>
> >> --
> >> http://iap.md, The future is open
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> >
> >
> >
> > --
> > S pozdravom (regards)
> > Ing. Peter Kukuča
> >
> > _______________________________________________
> > postgis-users mailing list
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> >
> >
>
>
>
> --
> http://iap.md, The future is open
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-- 
S pozdravom (regards)
Ing. Peter Kukuča
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