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    Re: Height by sextant angle
    From: Peter Monta
    Date: 2014 Dec 12, 13:57 -0800


    Frank writes:

    It all depends on the angular diameter of the Sun which is what determines the width of the "fuzzy edge" or penumbra of the airship's shadow...

    I suppose a single shadow edge is all that's required for an estimate of height, provided the shadow profile can be cleanly extracted or eyeballed from the underlying image.  Best to have actual dimensions of the airship, but if that's unavailable, the full shadow width divided by 30 arcmin is your height.  The sundial people use "shadow sharpeners" to get better visuals of the shadow profile, but that's not possible here.

    If the camera is known to be linear (or linear with some gamma), curve fitting could be applied to the edge.  People tend to overestimate or underestimate the half-intensity point on the shadow (I forget which).

    Cheers,
    Peter

       
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