NavList:

   

Reply

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
> ----------------------------------------------------------------
>

   

Reply