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: The Sun does not stop for anyone
    From: Gary LaPook
    Date: 2016 Dec 26, 11:20 -0800

    I understand that for absolute accuracy the small scale plotting sheet should not be called "Mercator" but then why, in all these years, has there not been a different name for it put forward in any of the navigation texts? You propose several names that I have never seen before in any text. Bowditch says that you can make a Mercator small area plotting sheet by using Meridional parts and then goes on to say "a good approximation can be more quickly constructed" using the described methods. "A good approximation" of what, of a Mercator chart. I think you may be being overly pedantic on this one, Frank.

    gl

    ---------------------------------------------------

    Time to scream. Arrrrrgh. No, that is exactly the big, fat error that navigators routinely make. Local scaling of longitude minutes to match latitude minutes is not the Mercator projection. That property describes a map that is locally conformal, but various map projections are locally conformal, not just Mercator. If you don't like the name "conformal," which is unfortunately not very transparent in meaning, then call it "longitude-scaled." Another name for it would be "similarity". On a locally conformal map projection squares look like squares, and triangles look like triangles. That is, the shapes portrayed on the map are "similar," in the sense of "similar triangles," to shapes drawn on the ground, in the real world. Note that this only applies locally, in a small area, on a Mercator chart. The best example of a failure to preserve shapes in the global Mercator chart is the rhumbline itself which is a spiral, a loxodrome, on the globe, but a perfectly straight line on the chart. In each very small local region shapes are portrayed correctly, but globally they cannot be.

       
    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