[Leica] Re: GPS

[lrzeitlin at optonline.net (Lawrence Zeitlin)]

On Feb 25, 2007, at 1:09 AM, Marc wrote:

> A decade back, the US Air Force and US Navy
> ceased requiring a knowledge of celestial
> navigation for navigators.  Still, these guys
> learn it, both for the elegance of it and for the
> hard reality that the GPS grid may be knocked out
> at any time by happenstance or evil intent.

At last a subject I know something about.

I learned celestial navigation in 1948 and served as a navigator on  
half a dozen Newport to Bermuda sailboat races during the '50s. I  
also taught navigation to NROTC cadets in a couple of colleges and  
used it on my own boat for long open water passages. However for the  
last couple of decades my beautifully made Heath Hezzanth sextant, a  
device as precise as the Leica M3, has been sitting unused on my  
closet shelf. It is a mistake to believe that celestial navigation is  
a backup to a GPS. While it is possible to navigate crudely  
(accuracy, plus or minus 50 NM) using only a sextant and a calendar,  
precision navigation (plus or minus one mile) requires a chronometer  
accurate to the second, an armful of annually updated books, a sharp  
pencil and pad, and a clear view of the sun or stars. It also takes  
several sightings and a few minutes of calculation to get a precise  
fix. If it is cloudy, fuggedaboudtit. That's a New Jersey technical  
term.

The GPS changed the rules of navigation. Through the magic of  
technology, using a cheap cigarette pack sized device, an untutored  
navigator could find his/her position with an accuracy of one meter  
anywhere on the Earth's surface. It worked day or night in clear or  
cloudy conditions. Using a photographic analogy, the GPS is  
equivalent to auto exposure, auto focus, auto wind cameras. "Real"  
photographers resisted automation for a long time but now we all use  
it except when we want to be deliberately "retro." In fact if you go  
into your local boating store or auto dealership you can buy a  
navigation system that not only tells where you are but plots your  
position on a map or chart and gives you the exact route to take to  
reach your destination. The whole package costs less than a used 50  
mm Summicron lens.

As far as knocking out GPS by hostile intent, it can only be done  
over a very limited area, i.e. over a city or a harbor. Usually the  
area is smaller than the accuracy limits of celestial navigation.  
Furthermore, alternative electronic navigation methods (e.g. LORAN)  
are even more useful than GPS in coastal areas. I'm glad the Air  
Force and Navy stopped training navigators in celestial navigation  
methods. Technology has demystified another arcane skill and saved us  
taxpayers a bundle of money.

Now we can talk about how digital cameras have impacted the darkroom  
culture.

Larry Z