[postgis-users] Postgis - Line to Point distance

[Pavel Iacovlev]

The length of the line, you can't calculate a distance between a point
and a line in general. You can calculate a distance between a point
and a point on a line.

ST_distance_spheroid(point, ST_line_interpolate_point(line,
ST_line_locate_point(line, point)),
'SPHEROID["GRS_1980",6378137,298.257222101]')

ST_line_locate_point(line, point) - a point on the line that is most
close to your initial point

ST_line_interpolate_point - get that point as a point geometry

ST_distance_spheroid - calculate the length between 2 points

2009/7/10 Peter Kukuča <pjr.kukuca at gmail.com>:
> 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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>> >> >>
>> >> >>
>> >> >>
>> >> >> --
>> >> >> 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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>



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