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Yes Dave, thanks,  you summarize what I was asking well. Clearly it
can be done "in theory". But depends on how good a camera, how steady
a ship, how dark a night.  Just an example. Suppose we can see on
average one star per square degree, and our super horizon camera can
see 360 degrees of horizon and one degree of altitude. We would have
around 360 stars. If they were spread evenly in altitude we would have
one for every  1/6  of a minute.  If we took the lowest 3 stars to
define the horizon we might expect to have the horizon to around 1/2 a
minute.  This is a very rough explanation as a proper statistical
technique would give better estimates and explicit error bars.

If it works there a few ways we could use it. Cameras on the same rig
looking at higher altitudes then give us data for conventional fixes
by altitude of stars for example but not limited to twilight to see
the horizon.

Bill


On Sat, 14 Dec 2024 at 18:31, NavList Community  wrote:
>
> Re: Estimating horizon from a photo on a clear night
> From: David Pike
> Date: 2024 Dec 14, 09:31 -0800
>
> Bill Lionheart
> You talked of estimating the position of the horizon at night from a photograph.
>
> Just to try and turn this into layman’s terms, are you saying that on a 
clear night you might be able to see the stars but be unable, for whatever 
reason, to work out where the horizon is, so you can’t use the stars to 
obtain position lines using a marine sextant?
>
> Therefore, take a photograph which includes the brightest recognizable stars 
and use this Hough technique to predict where the horizon might be on the 
photograph.  Then use a pixel count to find the Hs of a required star and 
thus a position line.
>
> An alternative approach might be to take a vertical photograph and use the 
same technique to predict your zenith at the instant the photograph was 
taken.  Then use pixel counts to measure zenith distances of all the 
brightest stars in the photograph.  Use these statistically to make a best 
guess of your position***.  DaveP
>
> *** ”How to bluff your way in Mathematics” by A Bloke I Know.
>
> 
>
>
>  

   

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