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    Re: New compact backup CELNAV system
    From: Ken Gebhart
    Date: 2009 Mar 17, 21:50 -0500

    Gary,
    
    The interest in your Bygrave project has been great and well
    deserved.  But when talking about "backup" systems, I think about one
    who is ill versed in CN, and just wants to make a safe landfall
    without his failed GPS.  In this situation, I feel that using simple
    noon sight procedures supplemented by sunrise/sunset longitudes, and
    polaris Lats would be fine.  All that would be needed would be the
    Nautical Almanac (for the Sunrise/ Sunset things) and would have the
    included SR Tables for intermediate sights.  One might not prefer
    these NA SR tables, but they DO work, and in a backup situation, why
    be choosey?
    
    Ken
    On Mar 17, 2009, at 6:26 PM, glapook{at}PACBELL.NET wrote:
    
    >
    > I am real happy that I kicked off this topic and am impressed by the
    > level of interest shown in using this simple to produce modification
    > of the Bygrave for a backup celnav system. I am also impressed by the
    > improved scales created by the other members on this list. A while ago
    > I contacted Ken Gephart at Celestaire to get his opinion on whether he
    > thought there would be any interest in a commercially produced version
    > but he didn't think there would be. He thought that a simpler system
    > would be better considering the lack of celestial training of your
    > everyday sailor. I started this discussion stating that it was meant
    > for those knowledgeable in CELNAV, the virtue of this system being its
    > compact size and its low cost. He said that if they already had the
    > Nautical Almanac they had the reduction tables already published in
    > the N.A. (I, for one, really dislike those tables, your mileage may
    > vary.) Work out an example with the N.A tables and compare the work
    > with the came computation with the Bygrave and I think you will agree
    > the Bygrave is easier to use. Those same non celnav sailors wouldn't
    > be expected to buy an N.A. every year either so another advantage of
    > this system is the long term almanac.
    >
    > So Ken, any more thoughts about this considering the great interest
    > shown on this list?
    >
    > gl
    >
    >
    > On Mar 17, 1:09 pm,  wrote:
    >> I am another long time lurker, who got all excited about Gary
    >> LaPook's flat Bygrave scales, and also got cracking on my own
    >> version of scales. Unfortunately it took me a while to complete
    >> due to distractions like family and job. So Dave beat me to it by
    >> a month or so.
    >>
    >> In any case I decided to publish my version of scales as well. Not
    >> because they are better than Dave's, but because they are written
    >> in Postscript, and can be easily customized by each individual
    >> user. It's easy to change width of scales to the size of your
    >> sheet or cylinder, number of lines, font size, frequency and
    >> thickness of tickmarks etc.
    >>
    >> The files cot.ps and cos.ps can be edited with text editor like
    >> notepad, and then converted to PDF using free Ghostview tool. To
    >> do that you also need to install Ghostscript. Here are links to
    >> download page.
    >>
    >> http://pages.cs.wisc.edu/~ghost/doc/GPL/gpl863.htmhttp://
    >> pages.cs.wisc.edu/~ghost/gsview/get49.htm
    >>
    >> You could even easily define other scales using this template e.g.
    >> sec()/csc() for Ageton method like Andrew suggested in one of the
    >> previous posts. Though this would require to write up the function
    >> in Postscript stack based form using just (sin, cos, and atan) as
    >> these are only available trigonometric functions in postscript. I
    >> would be glad to help, if somebody decides to do that.
    >>
    >> Note that common procedures for drawing the scale are in scale.inc
    >> file and it must be in the current directory when opening .ps
    >> files with ghostview.
    >>
    >> And I must also repeat Gary's warning, when printing PDF files
    >> make sure to set Page Scaling to None. I wasted few transparent
    >> sheets before figuring that out.
    >>
    >> Martin
    >>
    >>  cos.ps
    >> 1KViewDownload
    >>
    >>  cot.ps
    >> 2KViewDownload
    >>
    >>  scale.inc
    >> 2KViewDownload
    >>
    >>  cos.pdf
    >> 23KViewDownload
    >>
    >>  cot.pdf
    >> 85KViewDownload
    > >
    
    
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