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Re: Bowditch Table 15
From: Jim Thompson
Date: 2005 Jan 26, 16:34 -0400
From: Jim Thompson
Date: 2005 Jan 26, 16:34 -0400
I searched through the rest of Bowditch 2002 for more references to the Table 15 procedure, and found this odd paraphraph in Chapter 22, Article 2202: "Distance by vertical angle between the waterline and the top of an object is computed by solving the right triangle formed between the observer, the top of the object, and the waterline of the object by simple trigonometry. This assumes that the observer is at sea level, the Earth is flat between observer and object, there is no refraction, and the object and its waterline form a right angle. For most cases of practical significance, these assumptions produce no large errors. D = sqrt[(tan^2a/.0002419^2) + ((H-h)/0.7349)] - (tan a/.002419) where D is the distance in nautical miles, a is the corrected vertical angle, H is the height of the top of the object above sea level, and h is the observer's height of eye in feet. The constants (0.0002419 and 0.7349) account for refraction.". I don't see why the Table 15 equation is given in this paragraph. Looks to me like a chunk of text is missing between the end of "...produce no large errors" and the equation, and that in fact the second half, which contains the equation, belongs to a missing title that should describe "Distance by Vertical Angle Measured Between Sea Horizon and Top of Object Beyond Sea Horizon". Can someone check an older Bowditch? Jim Thompson jim2@jimthompson.net www.jimthompson.net -------------------- Outgoing email scanned by Norton Antivirus
