[Loadstone] Observations on Accuracy with Two Receivers

Shawn Kirkpatrick shawn at odyssey.cm.nu
Tue Oct 23 08:01:28 BST 2007


I've come accross this list as well. Unfortunately those measurements are 
kind of subjective. At least if you have a value in metres or feet you can 
judge for yourself if it's good enough.

On Tue, 23 Oct 2007, Rob Melchers wrote:

> 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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