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[DPRG] Using GPS HDOP for KF purposes
Subject: [DPRG] Using GPS HDOP for KF purposes
From: Dean Hall
dwhall256 at gmail.com
Date: Tue Jan 29 22:54:14 CST 2008
I still haven't found any information about the method of calculation
or the units (if any) of the HDOP value. Earlier, I *assumed* it was
meters. That looks not to be the case. I just re-read the Wikipedia
article. The DOP values do not indicate an error, but rather
"describe the geometric strength of satellite configuration on GPS
accuracy."
I believe this means that you can't get an accurate reading if your
DOP is high (because the sats-in-view aren't spaced about in your
favor); however, if the DOP is low, you have better satellite
geometry which allows the _opportunity_ for a more accurate reading.
But your actual accuracy is affected by many other factors and may or
may not be good.
I am running an experiment to compare positional error to the HDOP to
see if my [GPS unit, location, timing, local interference] fares any
better than Kenneth's and Dpa's. I just took the samples today over
a 1 hr period. I'll share the results when I get them.
I may be misunderstanding you, Kenneth, but I don't think pursuing
study of the HDOP value is preposterous. I found a value in the NMEA
data stream that hinted that it was related to the positional error.
I guessed (wrongly) that the value had units of meters based on data
that I had. I shared this initial information with the list. I am
following up with further study.
!!Dean
On Jan 29, 2008, at 21:15 , Kenneth Maxon wrote:
>
> My observation and comment back to Dean then about the perceived
> lack of
> correlation was that not only is the above preposterous, that when one
> actually runs those plots and looks at them graphically over any
> significant
> sampling the size of the HDOP error circles further away from the
> actual
> position are not larger and those closer are not smaller in any
> manner of
> consistent fashion. Additionally, at some of the extremes when the
> reported position wanders quite far away and then later repeats the
> quite
> far wandering the reported HDOP does not repeat either...
>
> -Just data for consideration. It was quite a disheartening
> observation,
> sigh...
>
> -Kenneth
>
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