[Gdal-dev] geod: azimuth to degrees

Jesse Cleary jcleary at email.unc.edu
Fri Nov 3 19:58:03 EST 2006

Hey Charlton -

I think you've already got what you need?  Geod outputs an azimuth, then 
a back azimuth, followed by distance.  The two azimuths are different 
(i.e. not complimentary like you might expect) because along a great 
circle route the azimuth changes throughout.  So you're given an initial 
azimuth beginning the route to Portland (-66d31'50.141", maybe better 
expressed as 360 - 66d31'50.141") and then the initial azimuth to begin 
a great circle route from Portland back to Boston (75d39'13.083").  At 
least that's what makes sense to me...

I've been using the perl Math::Trig module to do something similar and 
it works pretty well so far.  Might give geod a try to compare my 
results now though...


Charlton Purvis wrote:
> Thanks for getting back to me, Norman.  But I don't think that's what I'm
> shopping for.
> The geod command gives me the azimuth in lon,lat followed by a distance.  At
> least I think that's right.  So for my little arrow that I want to draw, I
> want to have a single degree value from 0 - 360 that is represents the
> azimuth.  It's that conversion that I don't know how to do.  The scaling
> part is a snap since geod gives that to me on a silver platter.
> Thanks for the help.
> Charlton
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