[postgis-users] Postgis - Line to Point distance

[Pavel Iacovlev]

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
>> >>> >
>> >>> >
>> >>> > ----------------------------------------------------------------------
>> >>> >
>> >>> > _______________________________________________
>> >>> > 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
>> >
>>
>>
>>
>> --
>> 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
>
> _______________________________________________
> 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