NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: 100:1 ratio distance measurements
From: Richard M Pisko
Date: 2003 Apr 5, 01:24 -0700
From: Richard M Pisko
Date: 2003 Apr 5, 01:24 -0700
On Fri, 4 Apr 2003 17:39:07 -0800, Royer, Doug wrote: >2.Accurate >measurement of the distance traversed (to the inch at longer ranges) while >moving the 10 mil angular distance is critical to keeping the measurement >consistant.I used a tripod and a plumb connected to the Bussol and measured >that distance from the start to the finish of the 10 mil angle. > I asked about the standard Soviet artillery compasses, because I couldn't remember the figure before, and they are generally graduated to 6,000 mils in a circle according to a source I believe. In other words, they essentially declared "Pi" was equal to an even "3" instead of 3.14159... the way it really is, or 3.200 the way the US military says it is. I have been making assumptions as to the amount of accuracy and portability you need, which may not be warranted. Rather than carry a tape and tripod to measure so accurately, walk through a 100mil arc and then the object will be away from you only ten times the distance you paced. Alternatively, if you can keep yourself on a straight course as on a road or with two bearing objects in line, the "broad and beam" angles of 45 degrees and 90 degrees to the third object with the unknown distance is probably easiest. This is just a special case of the "double angle" problem. Walk along a course "A-B" until the object "C" is at an angle of 45 degrees off to the right (or left) front. Start counting the paces while still heading along course "A-B" until "C" is off to the side at 90 degrees. Then "C" will be as far away from you as the length of the leg you measured. All of this should be explained with diagrams in a book of coastal navigation, along with how to use the sextant on its side to get the angles more accurately than possible with a hand compass. A cheap plastic sextant is not that heavy to carry with you while hiking, and is a lot of fun. It does not replace a map and compass, just makes (for example) planting and finding a cache a lot more accurate using at least three permanent natural reference objects not on a circle with your cache location. These can be hundreds of yards apart. An old survey text with references to plane tables and mapping will make the methods more clear. The most difficult job of locating yourself is with the stars, sun and moon as your only guides; then you also need accurate instruments, timepieces, and tables. Perhaps the easiest is with a good orienteering map of the area, with land forms such that you can recognize where you are without even a compass. -- Richard ...