[postgis-users] Postgis - Line to Point distance

[Pavel Iacovlev]

How about ST_line_locate_point(LineString, Point) ?

Returns a float between 0 and 1 representing the location of the
closest point on LineString to the given Point, as a fraction of total
2d line  length.
You can use the returned location to extract a Point
(line_interpolate_point) or a substring (line_substring).

And then with ST_line_interpolate_point(linestring, location),
interpolate that point and calculate the distance

2009/7/10 Peter Kukuča <pjr.kukuca at gmail.com>:
> 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
>> >> >
>> >> >
>> >> > ----------------------------------------------------------------------
>> >> >
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>> >
>> >
>> > --
>> > S pozdravom (regards)
>> > Ing. Peter Kukuča
>> >
>> > _______________________________________________
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>> >
>> >
>>
>>
>>
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>
>
>
> --
> S pozdravom (regards)
> Ing. Peter Kukuča
>
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>



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