NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2014 Jan 3, 13:29 -0800
Many of you may recall that Bruce Pennino brought his total station (theodolite) to Beavertail Point at the southern end of Conanicut Island a couple of months ago. We experimented with measuring height of eye and he demonstrated his direct measurements of dip. A large car carrier was headed in, getting ready to sail up into Narragansett Bay, and anchored briefly south of Newport. Bruce aimed the theodolite at the ship for a better look, and I held my phone up to the ocular to snap a few photos. Smartphone cameras take very nice images by this direct eyepiece projection technique since they have infinite focus by design. Here's a photo showing the big ship and the crosshairs. Given that the horizontal crosshair line sits on the true horizon, what can you figure out about this ship and other aspects of the observation? How far away is the ship? How big is it? Do you need to know height of eye (about thirty feet) to figure that out from this photo?
-FER
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