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    Re: Which calculator to use for "arctan(tan(269))"?
    From: Tony Oz
    Date: 2017 Jul 6, 01:14 -0700

    Robin Stuart on 2017 Feb 1, 08:40 said:

    Calculate
    <snip>
    Pol{ [ cos(Lat) · tan(Dec) - sin(Lat) · cos(LHA) ] , [-sin(LHA) ] }

    and then

    Hc = cos-1( r cos(Dec) ) and θ = Zn

    There is no need for a separate calculation of the altitude!!! One proviso, as Lars indicated, is that it only gives the correct answer for objects above the horizon.

    I attempted to feed this formula the coordinates (Lat, λ) of my location and Singapore's: 60°N,30°E and 1°17'N, 103°50'E - to see what it gives.

    To my surprise - the Hc obtained was exactly the GC distance between me and Singapore, coinsiding with the check calculation by the formula:

    d = arccos[sin(Lat1)·sin(Lat2) + cos(λ1)·cos(λ2)·cos(Lat1 - Lat2)]

    So, may be the Pol() calculator's function is much more usefull that I expected. I guess I must try it to see what Robin's and Lars's warning about being above the horizon means.

    Regards,

    Tony

       
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