NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: As we debate GPS reliability
From: Frank Reed
Date: 2009 Nov 13, 21:38 -0800
From: Frank Reed
Date: 2009 Nov 13, 21:38 -0800
Lu, you wrote: "Although it's not exactly clear what the fourth dimension is (Jeppsen says it's time, but then doesn't give an example of exactly how time figures in)" 4D navigation is all the rage in air navigation today. For air traffic, it makes a lot of sense since it's about saving fuel. A traditional flight from one city involves a climb at some fixed rate to cruising altitude, a cruise at that altitude, and then a descent to the destination airport. Supposedly, this 4D type of navigation creates continuous contours in space and time taking advantage of winds and the exact behavior of the aircraft's engines and aerodynamics that can significantly increase fuel efficiency. Heck, you'll arrive at the gate with just one drop of fuel left in the tanks (!!). Marine navigation can be highly optimized to take advantage of currents and avoid bad weather in order to reduce transit time as well as fuel consumption. Some of this is simple, and there's already a lot of software to do this. It's not so different from a road mapping program that finds the quickest path to your destination by putting you on the highway just to get across town even though your "instincts" might prefer a straighter path. I do await the day when a dozen boats all running the same software converge on the same offshore point simultaneously. I realize that software designers think of these things and write code with such issues in mind, but then there are those inevitable things called "bugs". I'm also waiting for a boat to turn up in Portland, Oregon instead of Portland, Maine. -FER --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com -~----------~----~----~----~------~----~------~--~---