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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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