[GRASS-dev] Re: [GRASS-user] How to find out an angle between to points on the map (for r.plane, r.lake)

GRASS GIS GRASS GIS developer
1

On Thu, Feb 28, 2008 at 7:26 PM, Hamish <hamish_b@yahoo.com> wrote:

Dylan Beaudette wrote:
> > Well of course I had to go and try this out.
> >
> > attached is a patch (against todays SVN) to optionally print the
> > bearing between clicks.

Hi,

you should add a check so that it won't allow bogus results if the
location is in Lat/Lon:

e.g. from d.grid:
if (geogrid->answer && G_projection() == PROJECTION_LL)
  G_fatal_error(_(".. option is not available for LL projection"));

(the great circle line's bearing changes with distance along it; unless
you are interested in the rhumbline?)

for this stuff also checkout m.cogo, r.transect, r.profile,
d.rhumbline, d.geodesic

Hamish

Thanks for the tips. Before I go and make any more modifications /
documentation additions does this small patch appear to be useful
enough to be merged into d.measure ? The m.cogo module is useful
enough, but sometimes an interactive quick approach (such as what
d.measure does) can be extremely useful.

Dylan