# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Figuring Course given Lat/Long of destination
From: Tony S
Date: 2000 Feb 28, 5:02 PM

```Ed:

OK on your first part. Let us know how things compare.

As for what Dr. Kolbe offered I'll bow to his follow-up explanation.
(hopefully he is watching). He is correct on what can be done on GC
using SR tables.

Tony

Ed Kitchin wrote:
>
> Thank you, Tony. I'll check my old Bowditch and look for the tables, and
> compare to the construction method to compare results. Meanwhile another
> writer stated that the great circle course could be found by " using a
> regular sight reduction table, substituting the lat./long of destination as
> the GP of a heavenly body." He then said to "crank the handle" and get the
> Zn as your great circle course. Now...I can do celestial nav. thanks to
> recently taken courses using HO 249, or the electronic calculator. I am
> trying to grasp this other guy's concept here. Seems though he is asking me
> to work backward through the process, given that sight reduction is to
> OBTAIN the GP, your distance off, and the Zn. Excuse my ignorance, but I
> can't grasp how to do that. What would you use then for the Hs, and what
> corrections would you apply? OR!!! (I just had this idea) You could enter HO
> 249 with the arguments: lat. of destination, and long. of dest. as
> declination, to obtain Zn - - but you would STILL need a corrected altitude
> (Hc). I have no idea. Would you help a rank beginner out with this one?
> Thank you.
>
> Ed Kitchin
> ----- Original Message -----
> From- "Tony"
> To:
> Sent: Monday, February 28, 2000 6:14 PM
> Subject: Re: Figuring Course given Lat/Long of destination
>
> > Ed:
> >
> > Well, not quite. I was really encouraging you to use the Bowditch
> > table methods. If you really want to plot this on a UPS what you
> > describe would be satisfactory.
> >
> > Do you have UP sheets for those latitudes?  If not you can construct
> > your own constant latitude sheet using Lo divisions as cosine of mid lat
> > in paper dimensions.
> >
> > Tony
> >
> > Ed Kitchin wrote:
> > >
> > > Thank you, Tony. In other words, I could construct a solution on the
> univ.
> > > plotting sheet, as I mentioned, but use the mean of departure, and
> > > destination latitudes, and that would work? Thank you.
> > >
> > > Ed
> > > ----- Original Message -----
> > > From- "Tony"
> > > To:
> > > Sent: Sunday, February 27, 2000 9:00 PM
> > > Subject: Re: Figuring Course given Lat/Long of destination
> > >
> > > > Ed:
> > > >
> > > > When you say that "there is the error of the Macerator thing", can you
> be
> > > > more specific?  Did you use Bowditch Mercator sailing by tables?  This
> > > > should work out OK.
> > > >
> > > > Actually, just using Plane sailing with mid-latitude should be quite
> close
> > > > because the distance is relatively short; only earth eccentricity is
> > > ignored.
> > > >
> > > > Why the problem suggests also GC (great circle) does not make much
> sense.
> > > > There would be less than a mile difference.  I did check the results
> by
> > > > computer and they are OK.  [ Sometimes they are not. ;) ]
> > > >
> > > > Tony    in San Francisco
> > > >
> > > >
> > > > > Ed Kitchin wrote:
> > > > >
> > > > > An interesting problem appears in the latest issue of "Ocean
> Navigator"
> > > Which asks that you figure
> > > > > the course to a destination given origination and destination. It
> would
> > > seem easy to determine the
> > > > > difference in lat. (The destination was over several degrees of
> lat.),
> > > but deg. of long. differ in
> > > > > length as you change lat. One could simply take the mean of the two
> > > given long. and use that, but
> > > > > that bothers me as not being all that accurate. There is the error
> of
> > > the Macerator thing. You
> > > > > could use universal plotting sheets and construct using a vertical
> > > representing diff./lat., then
> > > > > draw a horizontal from the top of the lat. fig., representing the
> long.
> > > at the destination, and
> > > > > draw a hypotenuse as the course line. (???) Are there any
> mathematicians
> > > out there to
> > > > >  give me a good formula to learn for this task? Thank you.
> > > > >
> > > > > Ed Kitchin
> > > >
> >
```
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