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The plot has the LoP and the confidence ellipse.
For the 1st iteration the center is the DR, s/e, position. The scale is 10 nm 
around this position. The plot is in a Mercator projection

I adopted the plotting method for PCs in:
- NavPac and Compact Data 2006-2010. ISBN 011-887331-8. HM Nautical Almanac Office. Stationery Office.
- Admiralty Manual of Navigation, Volume 2, BR 45 (2), Astro Navigation. 2004, 
TSO London. ISBN: 1-870077-65-2

For details about the coordinate transformation see: Two celestial LOPs Fix, at my website.

If you print the plot on a printer without the "fit to page" option, the 
angles, Z, are OK and distances are in scale. Do you have done this?
I cannot see any circle of position on the plot, are confused with the confidence ellipse?

Andr�s


-----Mensaje original-----
De: NavList@fer3.com [mailto:NavList@fer3.com] En nombre de George Huxtable
Enviado el: mi�rcoles, 11 de junio de 2008 15:30
Para: NavList@fer3.com
Asunto: [NavList 5399] Re: 3-Star Fix - "Canned Survival Problem"


I've been looking in a bit more detail at the diagram, provided with Andres 
Ruiz' computation, showing his resultant "cocked hat", and it's left me a 
bit puzzled.

I haven't found a way to print out that plot, so my comments refer only to 
the picture as I see it on my screen.

The final "fix" (affected as it may be by an error in the time of the Pollux 
observation, an error which isn't my present concern) is placed at the 
centre of the plot, at (0.0, 0.0) on the graph, so its actual lat and long 
are not shown on the plot, except as nearby text. But what are the x and y 
scales on that plot?

The y scale is simple enough. It shown changes in latitude, in minutes and 
in nautical miles , which are the same thing, positive going North. If 
angles measured on that plot are to mean anything, then the x axis should be 
to the same scale of miles on the plot, and so a position circle should plot 
as a circle. On my screen, that doesn't happen; a position circle plots as 
an ellipse, horizontally squashed. So on that picture, angles will be 
distorted.

What about the units along the horizontal scale, then? Although there's 
nothing to say so, those are plotted in nautical miles, also, even though 
that scale of miles differs from the miles of Northing. It's only possible 
to quantify shifts in longitude by doing some trig., and arithmetic.

To me, that appears to choose the worst of all possibilities. The two 
scales, horizontal and vertical, should be the same in miles, the vertical 
scale should be MARKED in minutes of lat. (as it is), and the horizontal 
scale should be MARKED in minutes of long., so that lat and long can be read 
straight off it.


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