Although I'm not a geographer, having looked at a globe I do know about longitude meridians running through the poles. ;-)
If you only had two longitude values you wouldn't even be able to calculate EW distance because of this effect. But if you know both the value for latitude and longitude at each of say two points, you know how close each is to the equator and so should be able to correct for the effect, doing some kind of great circle route type calculation. Or... Jerry -----Original Message----- From: Nikos Alexandris [mailto:[EMAIL PROTECTED] Sent: Thursday, December 13, 2007 2:27 PM To: Patton, Eric Cc: Gerald Nelson; Michael Misun; [email protected] Subject: RE: [GRASS-user] (kein Betreff) Just another piece of information (although don't remember where I read it): In general every 0.0001° of latitude equals ~ 11m. Longitude I think is the tough one... ;-) On Thu, 2007-12-13 at 14:12 -0500, Patton, Eric wrote: > The width of a degree of longitude varies by latitude; meridians of longitude converge to > a single point at the poles. Latitude varies as well, although considerably less so, due to > the rotation of the earth slightly squashing the poles, and bulging the Equator. > > ~ Eric. > > > -----Original Message----- > From: [EMAIL PROTECTED] on behalf of Gerald Nelson > Sent: Thu 12/13/2007 3:06 PM > To: 'Nikos Alexandris'; 'Michael Misun' > Cc: [email protected] > Subject: RE: [GRASS-user] (kein Betreff) > > I'm curious about the statement that "Lat-Long is not good to do distance > measurements" Someone else made a similar observation in a different > conversation recently too. I'm not a geographer so I'm probably missing > something but doesn't lat long just give you a point on the surface of the > earth and if you have two of these don't you more or less automatically know > the distance between them? > > Regards, Jerry > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Nikos Alexandris > Sent: Thursday, December 13, 2007 10:55 AM > To: Michael Misun > Cc: [email protected] > Subject: Re: [GRASS-user] (kein Betreff) > > Lat-Long is not good to do distance measurements! > > Why don't you reproject your lines in a "metric" projection system and > check the distances again. > > On Thu, 2007-12-13 at 14:03 +0100, Michael Misun wrote: > > hello everybody! > > i have a little problem: > > i want to set vertices on lines in a specified space (e.g. 2 km) in a lat > long coordinate system. > > i tried it with "v.to.points -vi .... dmax=0.03" and it works. the problem > is, that in the equatorial zone the space between the new added points is > about 1,7 km but up to the polzones the spacing is rather smaller and about > 600 m! > > can anybody help me with this problem? a want to have an equal space for > all vertices on my polylines > > > > michael -- Nikos Alexandris . Department of Remote Sensing & Landscape Information Systems Faculty of Forestry & Environmental Sciences, Albert-Ludwigs-University Freiburg . Tel. +49 (0) 761 203 3697 / Fax. +49 (0) 761 203 3701 / Skype: Nikos.Alexandris . Address: Tennenbacher str. 4, D-79106 Freiburg i. Br., Germany _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
