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Re: The Running Fix on an Ellipsoid
From: Andrés Ruiz
Date: 2017 Feb 5, 18:04 +0100

Dear colleagues,

First of all, one member of NavList published a paper.

Second, The Royal Institute of Navigation, is serious institution, and a peer reviewed procedure is used before publication.

So, I feel that we all should be proud of it.

...and is good for NavList.

I agree with Gary, in practical CelNav, the intercept method, MSH LoP, works fine under the assumptions of real navigation. Nothing new on the horizon.

The equation of a CoP is based on geodetic coordinates (geographical, astronomical); latitude an longitude, and geocentric ones; GHA and dec. And it is independent of the model used for our planet or others: sphere, ellipsoid or geoid.

Celestial sights give us geodetic latitude and longitude, no geocentric ones.

See: Vector equation of the Circle of Position

The worth of the paper is that shows moving, advance or retire, a celestial line of position is a bad assumption for general case and due to a mathematically correct approach. The intercept method is a good enough approach for this in the near surrounding.

If the whole problem is taken into account, the solution is as an engineering or astronomical problem:

Position and motion of a vessel from celestial observations Robin´s papers is a solution for two sights.

peer review is harder here :)

Best regards Robin.

Fair winds.

The only with i do not agree is the claim that: "On the sphere, points on the LoP all lie the same geodesic distance from GP; however this is not true for an ellipsoid".

I feel that comes from the geometric point of view: cutting the ellipsoid with a plane, but this is not the nature of the CoP.

Great thoughts!

Andrés Ruiz
Navigational Algorithms
http://sites.google.com/site/navigationalalgorithms/

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