NavList:

Frank,

You did read the next sentence where I said not really a fix. Two arbitrary latitudes near the observer can be used for time sight purposes to produce just the line of position as you describe but the chosen latitude doesn't have to be arbitrary when known from a previous or post observation.

How was Mr. Pigeon able to get his fix from a single observation ? Or is the timing of LAN really two observations in one ?

Greg Rudzinski

Re: Time Sight/LOP and Sumner Bracket
From: Frank Reed
Date: 2013 Nov 13, 13:33 -0800
Greg Rudzinski, you wrote:
"A time sight can be crossed with a LOP from the same observation to get a single observation fix."

Oh, come on... Of course not. I'm not entirely sure what you're doing, but it sure isn't that (that is, you may be doing something reasonable and you're just describing it incorrectly). A time sight, calculated twice with different latitudes, can produce a line of position. This does not contain any more information than the original time sight. And it does not produce a "fix" except to the extent that the two points that are connected to generate the line of position are both hypothetical fixes. A "time sight" calculation and a "line of position" are two sides of the same coin. They express the same observational content. You can't combine the two to get a fix unless you have multiple observations separated in azimuth --as always.

When you're trying to understand how a time sight is affected by latitude uncertainty and the azimuth of the sight, the best approach is to think about the equivalent line of position crossed with a hypothetical latitude line of position. Clearly if the Sun bears nearly east or west when you shoot the time sight, the equivalent LOP is nearly perpendicular to a latitude line. Therefore there is almost no uncertainty in the time sight from an uncertain latitude. By contrast, if we attempt to shoot a time sight close to the meridian, the equivalent LOP is nearly parallel to a latitude line, and any uncertainty in latitude yields a big uncertainty in the resulting longitude.

-FER
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