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    Re: Why no interpolation for Latitude/LHA in sight reduction tables?
    From: Greg R_
    Date: 2008 Jul 7, 22:26 -0700

    Gary LaPook writes:
    
    > In fact, H.O. 214 did have tables for interpolation for LHA and a
    > procedure for adjustment for minutes of latitude.
    
    Aha... I've never used 214 so I wasn't aware that the SR tables had
    those at one time - wonder if they were dropped in an effort to
    "simplify" the tables when 249 was released?
    
    > These adjustments can also be accomplished graphically just draw the LOP
    > through the AP and measure the perpendicular distance form this LOP to
    > the DR position..
    
    Correct... but then again that's also the "normal" way to plot LOPs. I
    was thinking it might make for faster/more accurate plotting if
    everything were interpolated first and just plotted from the DR
    position vs. the (several) APs.
    
    --
    GregR
    
    
    On Jun 29, 8:30 pm, "Gary J. LaPook"  wrote:
    > Gary LaPook writes:
    >
    > In fact, H.O. 214 did have tables for interpolation for LHA and a
    > procedure for adjustment for minutes of latitude.  H. O. 214 predated
    > H.O. 249 which copied 214's table arrangement, pages for latitude,
    > columns for declination and rows for LHA. In addition to 249's "d"
    > column of interpolation factors for declination, 214 had another column
    > of "t" correction factors for LHA (angle "t"). If you look at the "d"
    > correction values  in 229 and in 249 you will see that they are simply
    > the number of minutes between consecutive declination values (columns in
    > 249 and rows in 229) which allows you to do straight line interpolation
    > for intermediate values. H.O 214's "t" values also tabulated the
    > differences between successive LHA values to allow straight line
    > interpolation also. (H.O. 214 used 100 units instead of 60 units for "d"
    > and "t" values but the interpolation tables worked the same as in 249
    > and 229.) Since neither 229 nor 249 lists such "t" values it is not so
    > convenient to do this interpolation but you can determine the proper "t"
    > factors to use to interpolate for LHA by finding the difference between
    > successive values of LHA (easy with 249 since it is the next row down,
    > more inconvenient with 229 since you have to go to another page of LHA
    > values) and then use the same interpolation table you use to interpolate
    > for declination. H.O 214 then provided a table to correct for minutes of
    > latitude based on the azimuth.
    >
    > These adjustments can also be accomplished graphically just draw the LOP
    > through the AP and measure the perpendicular distance form this LOP to
    > the DR position..
    > gl
    >
    > Greg R. wrote:
    > > 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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