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: Showing a Mercator Projection is not a perspective projection
    From: Frank Reed
    Date: 2017 Jan 1, 11:54 -0800

    David P, you asked:
    "Do the points along them actually mean anything, or are the curves there just to indicate which latitude the yellow circles represent? "

    They represent the influence of a refractive medium with refractive index n(r) within the cylinder deflecting thr rays out towards the perimeter in the general Mercator projection.

    Ha ha ha ha. :) No, as you guessed, the curves simply provide a visual indication of the way in which the projected lines differ from the pure perspective cylindrical projection. But if you had to explain it to someone, you could say that it's "as if the rays are refracted outward by some medium in the cylinder that is less dense along the axis of the cylinder and more dense near the walls" --with a heavy emphasis on the words "as if"!

    By the way, I would have answered this question in my previous reply, but we were posting at exactly the same time (within a minute).

    Frank Reed

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a 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