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 <[email protected]> > you can take the middle of the line, st_line_interpolate_point(the_geom, > 0.5) > > 2009/7/10 Peter Kukuča <[email protected]>: > > 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 <[email protected]> > >> > >> -----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 > >> > [email protected] > >> > 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 > >> [email protected] > >> http://postgis.refractions.net/mailman/listinfo/postgis-users > > > > > > > > -- > > S pozdravom (regards) > > Ing. Peter Kukuča > > > > _______________________________________________ > > postgis-users mailing list > > [email protected] > > http://postgis.refractions.net/mailman/listinfo/postgis-users > > > > > > > > -- > http://iap.md, The future is open > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > -- S pozdravom (regards) Ing. Peter Kukuča
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