Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    Name or NavList Code:
    Email:
       
    Reply
    Re: Compare Methods: Lat/Lon Near Noon
    From: Antoine Couëtte
    Date: 2021 Oct 1, 12:52 -0700

    Dear Ed,

    You stated : "MOO also needs the Zn to the body".

    If I understand correctly your point, my reply would be: "yes and no", depending on the method you are using. But there will always be a final "no" in all cases in my reply.

    Referring to the enclosed document,

    (1) - If you use Option 4.0, my partial reply would be "yes" to your point. MOO needs the Zn's of the Body, at least to perform such  "preliminary and optional data processing" as described in 4.0 (see in particular 4.0.1.2). This preliminary processing involves correcting each individual height so as to cancel the effects of μDec and NS over some elapsed time from the same time origin. These effects can be adequately computed and cancelled with just only one condition : the Values of cos Zn are to stay almost equal to 1, which in fact they are (see 5.7.2.1.1). So, "yes" you need the successive Zn's, but only through their cosines. Since they all are assumed to be equal to +/-1 - which in fact they are - you actually do not explicitly use the successive Zn's values. This options enables you to process data for which UT Culmination = UT transit ( = UT LAN). But from there you are still to process some kind of quadratic curve regression.

    (2) - From this point, whether you use or not option 4.0, for your quadratic regression my full reply is : you do not need knowing the various Zn's.

    The quadratic curve your are fitting to your observations is derived from a series of (UT, Height) values, only from these.

    This Quadratic curve is here to compute H culm and UT culm, from which you derive H tran and UT tran through the appropriate Formulae. The quadratic curve does not explicitely need Zn's.

    (2.1) - If you start from "raw data" you will be using :

    (UT culm - UT tran) in seconds of time = (48 / π) * (tan Lat - tan Dec) * (μDec - NS) - (1a)

    (2.2) - Or if you start from " pre-processed data" you will be simply using :

    UT culm = UT tran 

    In all cases you are fitting you data to a quadratic curve having its symmetry axis "forced" to be exactly parallel to the heights scale axis. You just need (UT, Heights). No knowledge of Zn's is necessary.

    Hope I understood you point correctly and that it helps.

    If somebody can give his own explanations on this matter, e.g. Frank, I will certainly read them with attention.

    Best Regards,

    Antoine

    File:
    210915-Latitude-Longitude-Near-Noon-methods-comparison-.pdf
       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

    To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

    Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

    NavList is more than an online community... more about that another day.

    © Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

    Join / Get NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

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

    Email Settings

    NavList ID Code:

    Custom Index

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

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site