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 - 03:10:17 CET


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From: "R Knapp" <gyp_caver_at_yahoo.com>
To: "CaveXML" <cavexml_at_cartography.ch>
Date: Wed, 06 Feb 2002 21:10:17 -0500 (EST)
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Subject: Fwd: Re: http://www.ngs.noaa.gov/FGCS/BlueBook/ (fwd)
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Some of the discussion John and I have been having recently.

==================BEGIN FORWARDED MESSAGE==================
> From: "R Knapp" <gyp_caver_at_yahoo.com>
> To: "John Halleck" <John.Halleck_at_utah.edu>
> Date: Wed, 06 Feb 2002 07:49:28 -0500 (EST)

> > Before, you were talking about having an element with the raw value and a cononical
> > value. I think the canonical units were degrees for angles and meters for distance.
> > Is that correct? So for a distance element:
> >
> > <Distance value="10"/>
> >
> > the canonical representation you mentioned would be something like:
> >
> > <Distance value="10" canon_value="3.05"/>
> >
> > or
> >
> > <Azimuth value="N30E" canon_value="30.0"/>
> >
> > Is this correct?
>
> Yes. With the argument that if cannonical values exist then things
> later in the pipeline can be simpler and small utilities are easy
> to keep small.

It shouldn't be a problem to add them to the DTD, just repetitive (this is where Schemas
excel; I could create a new type with the canonical value there instead of repeating the
attribute for each element.)

I can see the value of the entry. This will add a bit (a very small bit) of burden to an
editor but that is all. And since it would be a one-way conversion, there should not be
as much a loss of precision as if it was two-way (due to rounding errors).

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).

- 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).

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

> > <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.
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.

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

        Richard Knapp
        gyp_caver_at_yahoo.com

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

        Richard Knapp
        gyp_caver_at_yahoo.com


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