[GRASS5] [bug #3145] (grass) R.profile does not use great circle paths

Hamish hamish_nospam at yahoo.com
Tue Apr 5 19:47:11 EDT 2005

> this bug's URL: http://intevation.de/rt/webrt?serial_num=3145
> ---------------------------------------------------------------------
> Subject: R.profile does not use great circle paths
> Platform: GNU/Linux/i386
> grass obtained from: Other (CDROM etc)
> grass binary for platform: Downloaded precompiled Binaries
> The r.profile command takes profiles along straight lines which is not
> correct if the surface the profile is being taken over is the
> projection of the earth's surface. In this case great circle paths
> should be taken.
> The simplest fix is to update the man page so it is clear that the
> angle between the starting and endpoints as if they were on a flat
> plane is used to calculate the intermediate points (At least this is
> what it looks like from the quick glance at the source code I took
> after I didn't understand the results I was getting). If a great
> circle was used then this azimuthal angle/bearing would change as you
> move along the path.
> Hope this helps

are you working in a lat/lon projection?

see also d.geodesic

 Displays a geodesic line, tracing the shortest distance between two
 geographic points along a great circle, in a longitude/latitude data

and d.rhumbline too.

great circle path should be an optional flag to r.profile,r.transect I
guess, or maybe automatic when PROJ=LL.


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