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
Glyn Edwards
-------------------------------------------- Managed by Request Tracker
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
Description:
Displays a geodesic line, tracing the shortest distance between two
geographic points along a great circle, in a longitude/latitude data
set.
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.