Fwd: Re: http://www.ngs.noaa.gov/FGCS/BlueBook/ (fwd)

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From: R Knapp (gyp_caver_at_yahoo.com)
Date: Thu Feb 07 2002 - 03:10:42 CET


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From: "R Knapp" <gyp_caver_at_yahoo.com>
To: "CaveXML" <cavexml_at_cartography.ch>
Date: Wed, 06 Feb 2002 21:10:42 -0500 (EST)
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Subject: Fwd: Re: http://www.ngs.noaa.gov/FGCS/BlueBook/ (fwd)
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More of same....

==================BEGIN FORWARDED MESSAGE==================
> From: John Halleck <John.Halleck_at_utah.edu>
> Sender: John.Halleck_at_utah.edu
> To: R Knapp <gyp_caver_at_yahoo.com>

On Wed, 6 Feb 2002, R Knapp wrote:

[ edited down quite a bit. )
> [...]
> Now, what units to use.
>
> - Should length be metric or English? Either choice w/could incur conversion back to
the
> other "base" for misc calculations (length, depth, etc).

  Which English? US feet or International (ISO) feet?
  At least their is only one metric system.
  (And before you think "who cares about the difference between US and ISO feet?"
  note that Larry Fish and Compass have had problems on just this issue for the people
  that need output referenced to their state plane coordinate system.)

> - Should angles be degrees or radians? Radians have the advantage of being friendly to
> computers (most functions like rads and not degrees) but again there might be a
> conversion back for misc calculations (rose diagrams, etc).

  I'd vote degrees. My weak argument is that at least degrees can be represented
exactly,
  any conversion to radians has to truncate. (And USGS used to have software that kept
  angles as seconds of arc, in an integer for similar reasons)

> Maybe there could be an attribute/element that specifies this information at the top of
> the XML file?

  As soon as it is specified at the top, then every diddly tool down the pipe has to
  be aware of it.
 
> > > <Position value="standing" location="bottle of ivory liquid">
> >
> > Huh?
>
> (An XML way of saying Standing on Soap Box. In my case, I use a bottle of Ivory Liquid
> since I usually fall off halfway through.)
>
> > > This was driving him nuts and I can understand why. I just don't want the final
data
> > > format.. whatever that might be.. to have the same issues.
> >
> > A value for precision takes care of this, no?
> > 3.1 in that case is really 3.1+-0.05 so a precison of 0.05 and a value of 3.1 would
> > be reasonable.
>
> I guess that depends. With a +-0.05m that could be as much as 0.1m between two shots.

  Yep. Which is the reality. (But remember that if length A has standard deviation
  of Sa and Length be has standard deviation of Sb then the two added together have
  a standard deviation that is NOT Sa+Sb, it is sqrt (Sa*Sa+Sb*Sb).
  (Basic error propogation theory, see any surveying book.)

> Thinking more about this later, I'm guessing COMPASS does not discard the extra decimal
> places; it just doesn't display them. Discarding them would be very bad.

  I agree.. and I've not yet caught Larry being that careless.

> Should this discussion head to the list? It's beens so quite there it might regenerate
> some interest.

  Up to you. My ability to respond is uneven at the moment. So one may or may not
  get timely responces.

  I've generally not been posting things to the list, since I've come to feel that my
  pedantic picking at assumptions was inhibiting some folks from posting.
  (And generally not serving a useful purpose.)

===================END FORWARDED MESSAGE===================

        Richard Knapp
        gyp_caver_at_yahoo.com


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