NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Almost a sextant
From: Frank Reed
Date: 2009 Dec 4, 14:57 -0800
From: Frank Reed
Date: 2009 Dec 4, 14:57 -0800
Bruce, you wrote: "Now there is an Iphone app that uses the camera to measure angles. Match that with celestial navigation apps and we would have our digital pocket sextant." But it's still an iKamal. And what I mean by that is that it is limited to the angular accuracy that can be obtained with any simple "angle-filling" device that is held in the hand. Expect no better than half a degree of acccuracy EVEN IF the internal vertical is absolutely accurate (and it's not). However, I do know a way of using -two- iPhones to make a good sextant. You see, the face of the iPhone is quite reflective :-). So we take two iPhones, power them down, affix them perpendicular to a backplate, one on a rotating arm, and then when held so that sunlight or starlight bounces from one iPhone to the next, the angle between a direct ray from the horizon and the reflected ray from the two iPhones will not change when it is rotated about an axis perpendicular to the backplate. Ha! Yes, it's just a sextant with the two iPhones being used as horizon and index mirrors. Until the phone can capture the video and analyze the image (presently it cannot except by hacking), the iKamal cannot beat the accuracy that comes from double-reflection. And also, needless to say but I will say it anyway, the accelerometers for determining the vertical in these new phones (many models now have them --not just the iPhone) are sensitive to observer accelerations unless some rather sophisticated processing is performed to average those out. -FER -- NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com