NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Learn the stars, by phone
From: Brad Morris
Date: 2009 May 14, 13:59 -0400
From: Brad Morris
Date: 2009 May 14, 13:59 -0400
A bit of caution, if you don't move by a significant displacement, then the heading displayed on a GPS is not to be trusted. The reason is pretty obvious. The dither in position due to the quantizing and sampling of the satellite signals will actually let your position wander about some nominal mean. In one experiment, I found this to be 150 feet, peak to peak in both NS and EW, for my particular GPS. If you sit still, and then turn on the GPS, the heading is just random, independent of actual heading. Once there is course made good, the GPS has two positions relative to time and naturally, a course. Best Regards Brad -----Original Message----- From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of James N Wilson Sent: Thursday, May 14, 2009 1:51 PM To: NavList@fer3.com Subject: [NavList 8270] Re: Learn the stars, by phone George: Your discussion of problems with compasses reminded me of an ancient experience--putting a compass in a tank. I headed a team to advise the army, and they were looking for a more modern way than the existing one: the tank commander stopped the tank, got out and walked fifty feet away and read his hand compass. They had been sold on a scheme which had an aircraft fluxgate compass on a fender, but it was awful. Deviation of up to 300 degrees! I couldn't believe it. The only way it worked was with the tank stopped on level ground pointing north. Not very utile. A general asked me could GPS be used to get a heading. I asked our JPL navigators about that, and they came up with two schemes that could do the job. Of course, that's common now, and a lot more. Jim Wilson ____________________________________________________________ Digital Photography - Click Now. "Confidentiality and Privilege Notice The information transmitted by this electronic mail (and any attachments) is being sent by or on behalf of Tactronics; it is intended for the exclusive use of the addressee named above and may constitute information that is privileged or confidential or otherwise legally exempt from disclosure. If you are not the addressee or an employee or agent responsible for delivering this message to same, you are not authorized to retain, read, copy or disseminate this electronic mail (or any attachments) or any part thereof. If you have received this electronic mail (and any attachments) in error, please call us immediately and send written confirmation that same has been deleted from your system. Thank you." --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---