NavList:

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

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
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

```
```

```

--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To unsubscribe, email NavList-unsubscribe@fer3.com
-~----------~----~----~----~------~----~------~--~---

Browse Files

Drop Files

Join NavList

 Name: (please, no nicknames or handles) Email:
 Do you want to receive all group messages by email? Yes No
You can also join by posting. Your first on-topic post automatically makes you a member.

Posting Code

Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
 Email:

Email Settings

 Posting Code:

Custom Index

 Subject: Author: Start date: (yyyymm dd) End date: (yyyymm dd)