# 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: Question Re: Position by Calculation
From: Peter Hakel
Date: 2014 Jan 6, 19:28 -0800
Sean,

This method indeed uses a common AP for all sights.  That should not be a problem here, because “by computation” assumes you are using a computer or a calculator to process your sights.   That way you don't have to use tables, which gives you the freedom to choose any convenient AP.  This method is implemented in the attached Excel spreadsheet described in:

in which all intercepts and azimuths are calculated internally.

That said, it is possible to convert a given intercept distance to an equivalent one relative to another AP with some 2-D geometry.

Peter Hakel

From: Sean C <yhshuh@aol.com>
To: pmh099@yahoo.com
Sent: Monday, January 6, 2014 1:57 PM
Subject: [NavList] Question Re: Position by Calculation

I was just using my new Kolbe LTA to complete a fictitious sight reduction problem of my own creation. I was pleased with the result which was 4.5 nm away from the actual position. (Bear in mind I purposely threw in a little random error.)
However, as is my usual practice I also ran the numbers using other methods to cross check my results. As one might expect Rodger Farley's "Teacup Celestial" program produced a fix much closer to the actual position. But I was curious about which part of my original calculations contributed most to the error. Was it the limitations of the concise sight reduction tables or maybe a plotting error on my part or just the random error I threw in? (I did remember to *add in the refraction and other corrections to the "raw" sight data.)
So, I decided to work backwards and start by checking the plot. I figured I'd cross check it by using my azimuths and intercepts to calculate the fix directly, which brings me to my question: Can the method described in the "Position from intercept and azimuth by calculation." section of the Nautical Almanac be used when you have different APs for each sight, as is required when using the concise tables, or is it necessary to have one single AP?
I'm no mathematician (to be honest, most of this seems like voo-doo to me), but my intuition tells me the latter would be the case. I say this because I notice there is only one instance of an AP lat/lon in the equations. Also, when I tried it I got a longitude that was very close to the actual, but the latitude was even farther off.
Thanks in advance for any insights!
Regards,
Sean C.
----------------------------------------------------------------
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com
----------------------------------------------------------------
View and reply to this message: http://fer3.com/arc/m2.aspx?i=126201

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)