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Subject: correct way to draw LOPs
From: Rick Emerson (rick@XXX.XXX)
Date: Tue Jun 22 1999 - 07:26:48 EDT
Russell Sher writes:
> Hi - is the corect way to draw an LOP a line with a arrowhead at each end?
> Or is it a single arrowhead pointing to the bearing of the object.
>
> Russell
An LOP is perpendicular to the bearing so drawing an arrow pointing
to the bearing isn't a hot idea. Typically, a straight LOP can be
drawn with an arrow at either end: <----------> while an advanced LOP
is drawn thus: <<---------->> The double arrows indicate the LOP is
advanced from an earlier LOP. Mark the initial LOP with time and date
(if the LOP is a celestial LOP, I add the appropriate symbol for the
body used to obtain the LOP) and mark both the initial and later time
stamps on the advanced LOP. The idea is to be able to determine what
data lead to the LOP's; some days it's useful to figure out where
(horrors!) an error came from.
The distinction about straight LOP's is made because there are also
arc LOP's based on range from a point where the bearing is uncertain.
A LORAN fix, for example, is really three intersecting arc (well,
hyperbolic) LOP's where range is based on time delays. Other examples
include radar ranges and ranges determined by measuring the angle
between the horizon and top of an object of known height (e.g.,
lighthouse).
Rick
S/V One With The Wind, Baba 35
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