NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: That darned old cocked hat
From: UNK
Date: 2010 Dec 10, 22:53 +0000
From: UNK
Date: 2010 Dec 10, 22:53 +0000
This post reminds me of what happened long after the Board of Longitude had paid out their price: There was no end to the submission of "better" solutions. Herbert Prinz On 2010-12-10 22:22, Gary LaPook wrote: > > So we now have four geometric constructions (plus visual estimation > making a total of 5 ways) to plot the fix inside the cocked hat. John > Karl's probability diagram shows the probability of each of these > points to be essentially equal although the Symmedian point my be ever > so slightly more probable. So, what method should you use? I think the > decision should be based on ease of construction. Obviously the > easiest way is by eyeball and is the method I recommend. The next > easiest construction is my method of determining the centroid by the > "median" method. You only have to use dividers to halve one of the > LOPs, lay a straight edge from the opposite corner to this point, and > then use the dividers to mark the 2/3rds point along the straight > edge. The standard way to determine the centroid is the text easiest, > halve two of the LOPs and draw the two lines from the opposite angles > to those points. More difficult is measuring the angles of two of the > three corners, then dividing them in half, and then finally plotting > those lines. ( You can also find the bisectors of the azimuths and > plot them, you get the same point, if the spread of azimuths exceed > 180 degrees.) The most difficult point to plot is the Symmedian point > which requires that you first plot both the medians and bisectors, > measure the angle between each of the lines in each set, and then draw > in the additional lines shifted by the angle between the lines in each > set to the opposite side of the bisector. Plotting the Symmedian point > takes a lot more work with no significant in probability that it > represents the actual position of the vessel. > > ( See my diagrams on the "three body fix" thread.) > > gl > ---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------------------- >