[Loadstone] Observations on Accuracy with Two Receivers

Rob Melchers rob at loadstone-gps.com
Tue Oct 23 07:44:38 BST 2007


This is a list that I found several times on the net:

DOP Rating Description

1: Ideal
This is the highest possible confidence level to be used for applications 
demanding the highest possible precision at all times.
2-3: Excellent
At this confidence level, positional measurements are considered accurate 
enough to meet all but the most sensitive applications.
4-6: Good
Represents a level that marks the minimum appropriate for making business 
decisions. Positional measurements could be used to make reliable in-route 
navigation suggestions to the user.
7-8: Moderate
Positional measurements could be used for calculations, but the fix quality 
could still be improved. A more open view of the sky is recommended.
9-20: Fair
Represents a low confidence level. Positional measurements should be 
discarded or used only to indicate a very rough estimate of the current 
location.
21-50: Poor
At this level, measurements are inaccurate by as much as half a football 
field and should be discarded.

http://www.codepedia.com/1/Geometric+Dilution+of+Precision+(DOP)

At 10/22/2007, you wrote:
>There's talk about it somewhere on this list, I think someone pointed out a
>wikipedia entry about it somewhere but I don't have the link at the moment.
>Getting exact information on how to do these calculations seems pretty much
>impossible from what I can tell unless I'm not looking for the correct
>information. The method we're using seems correct but who knows for sure.
>The accuracy values are just an estimate from the receiver anyway so that
>could be off as well.
>
>On Mon, 22 Oct 2007, Kevin Chao wrote:
>
> > What is this user range error?
> >
> > I have read of various other equations and ones that require integrals and
> > simations, but not ones that use the "user range error."
> >
> > Kevin
> >
> > -----Original Message-----
> > From: loadstone-bounces at loadstone-gps.com
> > [mailto:loadstone-bounces at loadstone-gps.com] On Behalf Of Shawn Kirkpatrick
> > Sent: Monday, October 22, 2007 5:19 PM
> > To: loadstone at loadstone-gps.com
> > Subject: Re: [Loadstone] Observations on Accuracy with Two Receivers
> >
> > The equation for getting the accuracy in metres is to multiply the hdop by
> > the user range error setting. The same goes for the vertical accuracy,
> > multiply vdop by user range error. The conversion to feet is done if the
> > user has it set to use imperial. I'm not completely sure if this is the
> > correct equation but I think it is. Vertical accuracy is a lot less 
> accurate
> > but that's up to the receiver.
> >
> > On Mon, 22 Oct 2007, Kevin Chao wrote:
> >
> >> I am sure that the hdop reading is taken into account when reporting
> >> the accuracy in number of feet.
> >>
> >> I am wondering what equation is the LoadStone team using to take the
> >> hdop value and giving the user a number of feet?
> >>
> >> Is there a similar equation that can be used for the vdop? I know that
> >> the vertical reading is a lot more flakey and less accurate, but just
> > wondering.
> >>
> >>
> >> Thanks,
> >>
> >> Kevin
> >>
> >> -----Original Message-----
> >> From: loadstone-bounces at loadstone-gps.com
> >> [mailto:loadstone-bounces at loadstone-gps.com] On Behalf Of Michael O.
> >> Hanson
> >> Sent: Monday, October 22, 2007 1:25 PM
> >> To: loadstone at loadstone-gps.com
> >> Subject: [Loadstone] Observations on Accuracy with Two Receivers
> >>
> >> Changing accuracy from a number to a number of feet was a great
> > improvement.
> >>
> >> I don't want to start the great GPS receiver controversy or anything
> >> like that.
> >>
> >> Some users might find the information below helpful.  I do not claim
> >> that these test results are anything close to conclusive.  They are my
> >> observations.
> >>
> >> My testing was not performed under scientific or controlled conditions.
> >> Other users could get vastly different results for any number of reasons.
> >>
> >> I tested a Holux M-2000 and a Royaltec RBT-2110.  I tested both
> >> receivers in my living room and outside.
> >>
> >> The Holux got average readings of between twenty and thirty feet.  The
> >> lowest was 20.8 feet.  The highest was thirty feet.
> >>
> >> The Royaltec got readings of between fifty-five feet and ninety-four feet.
> >> The lowest was fifty-four feet.  The highest was ninety-six feet.
> >>
> >> The Holux averaged eight to ten out of twelve satellites.  The
> >> Royaltec averaged four out of twelve.
> >>
> >> I know the Royaltec is somewhat better at tracking direction changes.
> >> It is a perfectly usable receiver in my experience.  If there is some
> >> factor I am not taking into account, please let me know.
> >>
> >>
> >> Mike Hanson
> >>
> >>
> >>
> >>
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> >>
> >>
> >>
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