Re: [Phys-l] polar grid navigation - more gratuitous notes....

[brian whatcott <betwys1@sbcglobal.net>]

Ah! Ken Caviness offers a moderate note of reason,  requesting an end to 
this long drawn out thread.
But is that the Phys-L way?     No indeed!

It's interesting (to me)  to mention that some current 
commercial/military aircraft types which fly the trans-polar routes have 
found unexpected visits with the polar singularity gremlins via their 
FMS (flight management System) displays. Even closer to home, some 
flight simulators  provide instructors a north up map of flight tracks. 
Approaching the poles, they hold onto their spherical trig until the 
trig numerator of some calculation grows vanishingly small. It's a 
standard gotcha which quaternions and the system of nine trig equations 
used for coordinate transformation can easily avoid, but otherwise, it's 
problematical.
And seeing a great circle transform to a parabolic (??)  track is 
disconcerting - but not so disconcerting as attempting to display 
north-up,  a track starting at the pole (this is quite likely to display 
as an aircraft flying sidewards to the "West" for example!

Brian W

On 2/16/2012 7:10 AM, Ken Caviness wrote:
> Thanks for the links!  I particularly like the LuAnn Dahlman's blog with maps showing the difference between "Grid North" and "True North".   I also note that in the accompanying paragraphs, there are statements like this:
>
> "When I focus in on our location on these maps, my brain has to do a mental transformation so that I don't interpret down as south."
>
> Clearly _she_ is not confusing true north with grid north, or grid south with true south.
>
> If the direction from the South Pole to Lake Vostok had been given in the media as "grid east-southeast" it would have provided a clear indication that some local coordinate system was being used, there would have been no confusion between that direction and "east-southeast".
>
> Where did the confusion enter?  When I speak about my own field with those without the background in it, I do try to explain terms I use, but sometimes Fachsprache terms, abbreviations, etc., creep in.  So I can picture an Antarctic scientist saying "east-southeast", forgetting that the news reporter would not understand the "obvious" meaning "grid east-southeast".  A mistake of omission.  But more likely the scientist interviewed would give a perhaps too extensive explanation, the reporter's eyes would glaze over, and he would simply use the map as if it were oriented "like all maps", and not seeing the glaring paradox of heading southeast from the South Pole would pass on his own misunderstanding to the public!
>
> A mistake was made, whether a mistake of omission or a mistake of miscomprehension.
>
> In answer to the question posed -- "What more do you want?" -- I have a simple answer:  now that it is apparent that the issue is semantics ("south" used in two different ways in the phrase "east southeast of the south pole", once as a "grid direction", once as a "true direction", I want to go back to my regularly scheduled life.
>
> Hey! -- I can do that without waiting for anyone's permission.  Hurrah!  I just made my day.  :-)
>
> Ken Caviness
> Physics@SAU