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
