[postgis-users] Postgis - Line to Point distance

Peter Kukuča pjr.kukuca at gmail.com
Fri Jul 10 01:52:45 PDT 2009


That is no good as well. If the point is a few meters from the line starting
point, then this would result in a distance equal to 1/2 of the line length
instead of a few meters

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

> 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
> >> >
> >> > ----------------------------------------------------------------------
> >> >
> >> > _______________________________________________
> >> > postgis-users mailing list
> >> > postgis-users at postgis.refractions.net
> >> > http://postgis.refractions.net/mailman/listinfo/postgis-users
> >> -----BEGIN PGP SIGNATURE-----
> >> Version: GnuPG v1.4.7 (GNU/Linux)
> >> Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org
> >>
> >> iD8DBQFKVv052FH5GXCfxAsRAqS1AJ0dfphFX3wrMuo+FdXVRTgmUzHRUACfUmvH
> >> 146yGHfxoVmlnt9a91rpWmE=
> >> =G70f
> >> -----END PGP SIGNATURE-----
> >>
> >> _______________________________________________
> >> postgis-users mailing list
> >> postgis-users at postgis.refractions.net
> >> http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
> >
> > --
> > S pozdravom (regards)
> > Ing. Peter Kukuča
> >
> > _______________________________________________
> > postgis-users mailing list
> > postgis-users at postgis.refractions.net
> > http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
>
>
>
> --
> http://iap.md, The future is open
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>



-- 
S pozdravom (regards)
Ing. Peter Kukuča
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-users/attachments/20090710/c570fd56/attachment.html>


More information about the postgis-users mailing list