NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/rec/boats/8814

Internet Message Format | 1992-12-30 | 3.8 KB

Path: sparky!uunet!mcsun!sun4nl!orcenl!nl.oracle.com!kverruyt
From: [e-mail] (Kees Verruyt)
Newsgroups: rec.boats
Subject: Re: Celestial vs. GPS (was Re: Bermuda Trip - 7/'93)
Message-ID: <[e-mail]>
Date: 30 Dec 92 13:51:36 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]>
Sender: [e-mail]
Organization: Oracle Europe
Lines: 68
Nntp-Posting-Host: nlsu54

In article <[e-mail]>, [e-mail] (Robert Hanners) writes:
|> In rec.boats, [e-mail] (Roy Smith) writes:
|> >[e-mail] (Dennis Bartley) writes:
|> >> You really don't have to be a rocket scientist to use Loran or GPS,
|> >> and with just a little thought you can tell the position it's giving
|> >> is in error.
|> >
|> >        I think part of the problem is that most people don't understand the
|> >difference between precision and accuracy, and assume that just because a
|> >Loran shows you your position to 1/10th (or even 1/100th) of a minute it
|> >must be correct.
|>
|> I'm not too familiar with the features on Loran and GPS but I do have
|> an appreciation of the potential error propagation that these devices,
|> especially the former, possess.  Intrinsic to the position calculation
|> algoritm of the unit is the ability for the unit to calculate range from
|> the transmitters and, depending on the memory/cost, some degree of the
|> propagation perturbation potential (percent range over land, for example).

Of course, that's one of the reasons why I like GPS better - since there are
more satellites than the three needed for a 2d fix, some of the errors are
averaged away (hopefully).

|> Also there's the direct ability to calculate potential error due to
|> nearly parallel intercepts and of course the unit can get a direct read
|> on signal strength.
|>
|> My question is this: Why isn't it reasonable for the unit to calculate and
|> display a measure of this potential error, as individual values (for
|> the discerning user :-) ) or as a total?  Or is this in fact a feature
|> of some makes?  The error itself could be a statistical measure such
|> as 50%, standard deviation, 2 x sd, or whatever.  Preferrably such
|> weighting would be user selectable.

You're quite right -- and so think some of the GPS manufacturers since I
remember that at least one brand has the ability to display such an error-value.

Don't remember which one though. I probably saw it at the Paris (France) Boat
Show, where I must have seen at least 20 different brands of GPS equipment.

|>
|> Now I do appreciate some of the difficulties in affixing real values to
|> some types of error and that some kinds of error cannot be reasonably
|> quantifiable at all.  (This would be an advantage of displaying individual
|> errors rather than simply the total.)  But it seems that manufacturers
|> might see that the advantage of such analyses for the knowledgable sailor
|> would outweigh the perception to the less knowledgable user that their
|> instrument is "error prone".
|>
|> What do you think?

Well I won't buy a GPS if it doesn't show me at least some indication of how
large the error is.

|>
|> -- Bob
|>
|> ------------------------------------------------------------------------------
|> Robert J. Hanners         "My comments; only mine."          *DIASTOLE* 676673
|> CD, NSWC, Annapolis, MD                              [e-mail]

--
------------------------------------------------------------------------
Kees Verruijt                           Rijnzathe 6
Software Engineer Gateway development   3454 PV  DE MEERN
Oracle Europe                           The Netherlands
Email: [e-mail]           Tel: [phone]
   or: [e-mail]               Fax: [phone]