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    Re: Why no interpolation for Latitude/LHA in sight reduction tables?
    From: Gary LaPook
    Date: 2008 Jul 09, 03:15 -0700
    That is the same methodology and formulas used to print the "Motion of the observer" and the "motion of the body" correction tables in H.O 249.

    gl

    Thomas Kleemann wrote:
    It's a little late but I'll jump in here.
    
    To achive a correction for the intercept from AP to DR
    one can assume some simplification:
    
    Because intercepts are usually short (less than 45 nm)
    plane geometry is sufficiently applicable.
    
    The following formula won't change the Azimuth or move your LOP at all,
    only the intercept is corrected for the other position it starts from.
    
    Delta I = Delta LHA * sinAz + Delta Lat * cosAz
    
    It can be done by tables, a natural sine table has you left with two
    multiplications, whereas a logarithmic sine table uses sums only.
    
    Don't get confused by the term 'Delta LHA', thats the difference between
    your longitudes AP vs DR, expressed by the minutes you round the LHA up
    or down for AP. This way you spare one calculation.
    
    /Thomas
    
    P.S. I haven't looked after it, but, maybe the old traverse tables are
    of some use here.
    
    
    
    
    
    Greg R. schrieb:
      
    Here's something that I've wondered about for a while: Does anyone know
    why there aren't interpolation tables for Latitude and LHA in the sight
    reduction tables (as there are for Dec)? Seems like if there were, we
    could just use the DR position as the AP - which would also make for
    faster position-finding since there wouldn't be a need to plot
    individual APs for each of the sights.
    
    Might have something to do with the limited amount of computing power
    available when the tables were first created (as was discussed with the
    reason why Pub 229 is LHA-oriented), or maybe Latitude and LHA don't
    vary linearly between even degrees - but I was curious if anyone knew if
    there was some reason for it.
    
    --
    GregR
    
    
    
        
    
    
    
    
      


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