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
    or...
       
    Reply
    Re: camera sextant?
    From: Marcel Tschudin
    Date: 2010 Jul 8, 01:17 +0300

    Greg,
    
    Yes, there seem to be small systematic contributions but I think your
    calibration measurements are quite good. Your figure represents a
    "calibration function" which tends to be a quadratic, not linear, as
    you have drawn it. They seem to be quadratic as George has indicated
    it in his figures showing their possible extrapolation. In my opinion
    your "outliers" are "normal" points indicating only the curvature.
    Part of the "problem" is here that we deal with digital photos.
    Differences can only be 0, 1, 2 etc. pixels. A possible way to improve
    this would consist in taking several measurements of a position in a
    photo and use the mean value. If we accept the "calibration function"
    to be quadratic, then I would assume that most measured HEIGHTS (your
    data points) would be within +/-1.4 pixels, corresponding to POSITIONS
    being measured to +/-1 pixel.
    
    The 1 pixel difference to your previous measurements may have various
    reasons. I tend to attribute  to your learning curve ;-) It could
    however be an indication to use for this sort of calibration
    (calibration by calculated positions) observations made at different
    days.
    
    Marcel
    
    
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    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)

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