[GRASS-user] (kein Betreff)

[Gerald Nelson]

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:nikos.alexandris at felis.uni-freiburg.de] 
Sent: Thursday, December 13, 2007 2:27 PM
To: Patton, Eric
Cc: Gerald Nelson; Michael Misun; grass-user at lists.osgeo.org
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: grass-user-bounces at lists.osgeo.org on behalf of Gerald Nelson
> Sent: Thu 12/13/2007 3:06 PM
> To: 'Nikos Alexandris'; 'Michael Misun'
> Cc: grass-user at lists.osgeo.org
> 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: grass-user-bounces at lists.osgeo.org
> [mailto:grass-user-bounces at lists.osgeo.org] On Behalf Of Nikos Alexandris
> Sent: Thursday, December 13, 2007 10:55 AM
> To: Michael Misun
> Cc: grass-user at lists.osgeo.org
> 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