[gps-talkusers] Re: Comparing two GPS elevation readings

Hello everyone
Two identical receivers will not have identical paths in 3D space so this is to be expected, and from what you have said these results look normal and is not a result of the platform but more to do with the receiver themselves. I would guess that if you switched receivers between the two units your results would flip flop, that is if you could do it at the exact same time which is impossible to do. The best you could do is start averaging the altitudes over 10 minutes, switch receivers between the systems, average again for another 10 minutes and if the results aren't clear cut switch the receivers a few more times also averaging the altitude and I am sure over the long run they will be either the same within a small variation, or you will find that one receiver consistently report an altitude x number of feet differently than the other receiver.
I would be very surprised if you found that switching receivers and averaging like I suggest results in one device (PK or the Voice Sense) consistently having the lower altitude reading compared to the other. 

Thanks
Charles.



At 11:05 AM 12/18/2008, you wrote:

Yes, but all things being equal, I find it interesting that they didn't come
up with the same variation.
I doubt there was one full second between my hitting the command on one,
then the other.
I realize GPS accuracy has that much variation.  It was more a comment about
the differences between the two units using the same model receiver,
reporting the same number of satellites, etc.
When it isn't snowing outside, I'll try it outside where they will certainly
get a clear shot at the sky.
We have no tall buildings around us.

Thanks,
Richard


-----Original Message-----
From: gps-talkusers-bounce@xxxxxxxxxxxxx
[mailto:gps-talkusers-bounce@xxxxxxxxxxxxx] On Behalf Of Ari Moisio
Sent: Thursday, December 18, 2008 10:48 AM
To: gps-talkusers@xxxxxxxxxxxxx
Subject: [gps-talkusers] Re: Comparing two GPS elevation readings


Hi Richard

  GPS altitude accuracy  is not as good as vertical  accuracy and depends
heavily on location of satellites. 20 to  30 meters (60 to 100 ft) is  a
typical altitude error and there might easily be more than 50 meters
variation within few minutes especially if the receiver does not have  a
good view to the sky.


--
mr. M01510 & guide Loadstone-GPS


On Thu, 18 Dec 2008, Richard Turner wrote:

> Greetings,
>
> I was curious about the elevation at our house due to some odd weather we
> are having.
> I have a Voice Sense with the latest Sense Nav, and a BrailleNote PK
running
> Sendero 5.2.  Both units are using a Holux m1000.
> Having them sitting side by side and the receivers in a window sill also
> side by side; the Voice Sense says we are at 269 feet, the PK says 226
feet.
> They both reported 18 feet accuracy with 9 satellites.
>
> I find that interesting.  Is that one of the differences with the 5.2
> release that may disappear once the Sense Nav is updated to the newest
SDK?
> Assuming they are going to do that of course.
>
> Thanks,
> Richard
>
>
>
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Charles M. La Pierre
CTO Sendero Group
"The GPS company:" Featuring Sendero GPS on the BrailleNote as well as Sense Nav and the new Mobile Geo for Windows Mobile devices. Also distributing Trekker, Victor Stream, KNFB Mobile Reader, Talks, Mobile Speak, Tiger embossers, Miniguide and ID Mate 
1-888-757-6810

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