NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Fix Maximum Probability Positions
From: Hewitt Schlereth
Date: 2013 Mar 26, 14:45 -0700
From: Hewitt Schlereth
Date: 2013 Mar 26, 14:45 -0700
John- It's always seemed to me that data based on the onboard compass and log are better than data from tide tables and pilot charts. After all, tide tables give the time the tide changes in a computer algorithm, the pilot charts show the long-term averages for winds and currents. Neither can tell you what is actually going on around you at your present place and time. Distance run and course steered, on the other hand, are based on direct reading of on-board instruments at your present time and place. If you keep a DR based solely on compass and log, the distance between your DR and LOP has the net of all the instrument and personal errors and all the effects of wind and sea. When DR and LOP are in front of you, THEN is the time to use any additional information and make a judgement as to whether or not the position makes sense. Hewitt Sent from my iPad On Mar 26, 2013, at 1:50 PM, "John Karl"wrote: > Hewitt, > > Yes in the estimation approach, one uses all the info available PRIOR to acquiring the new, and more accurate, LOP. There's nothing wrong with ignoring currents and drift if there's no info on them, or if you simply chose to. Then the location of the EPRF along the new LOP has that uncertainty built in, as well as the normal uncertainty. But that EPRF is still the best Rfix with the data used. > > And yes, the distance between the EPRF and the TP (DR, etc.) is a measure of the component of error in the direction perpendicular to the LOP. And there's no info on error along the LOP. > > But the traditional running fix gives no error information. > (The error is all in its assumptions.) > > JK > ---------------------------------------------------------------- > 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 > ---------------------------------------------------------------- > > : http://fer3.com/arc/m2.aspx?i=123119 > >