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PDOP column
#1
Hello

Some GPS devices do record the GPS PDOP.
In this case, the GPX file records the PDOP together with the position details, as shown in the following example:
------------------------------------------------------
trkpt lat="42.419265" lon="2.871295">
<ele>113.0</ele>
<time>2013-11-29T11:02:22.000Z</time>
<name>Position 2</name>
<pdop>1.15</pdop>
------------------------------------------------------
It will be nice to have the option to show this PDOP value in the columns.

Thanks and regards
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#2
(29.11.2013, 22:10)Alf Onico Wrote: It will be nice to have the option to show this PDOP value in the columns.

Do you really check the PDOP of your tracks? What would be the value of showing this information to you?

To be honest I cannot reproduce what are good and bad values without consulting wikipedia. And the German version doesn't contain that table that summarizes it.
--
Christian
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#3
Hello

Many thanks for your fast replay.

I often walk under heavy tree cover, or in deep valleys. Most satellites are therefore masked. A few ones are still visible, but their geometry could be more or less good enough to give a reasonable position.
When looking at the recorded track, I often wonder "where was I actually, the track doesn't seem to make sense but perhaps yes ?"
Then by looking at the PDOP of the position I can see if the satellite geometry available was good enough to give a reasonable position and decide if the recorded portion of the track does actually represent where I was.

I am not sure if your answer says that there is a doubt about what PDOP is.
Here after some answers.
Please excuse me if this was already clear for you and I misunderstood the doubt.
PDOP definitions:
http://rmbl.info/gis/whatispdop_.html
" PDOP stands for Positional Dilution of Precision. It indicates the accuracy of a 3D GPS position based on the number of satellites and the geometry of satellite positions. PDOP ranges from 0-99. The lower the number, the more accurate the data"
Also:
http://nptel.iitm.ac.in/courses/Webcours..._3GDOP.htm
"DOP is an indicator of three dimensional positioning accuracy as consequence of relative position of GPS satelllites with respect to a GPS receiver"

http://www.answers.com/topic/position-di...-precision

Best regards
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#4
(01.12.2013, 14:10)Alf Onico Wrote: I am not sure if your answer says that there is a doubt about what PDOP is.

It was more about: I cannot tell from memory when a DOP value indicates a good measurement from the GPS device and when to doubt the position that the device records. And if I cannot do that, the vast majority of the RouteConverter users won't be able to do it. So adding a column would bring more questions and no value to the average user.
--
Christian
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#5
(02.12.2013, 08:33)routeconverter Wrote:
(01.12.2013, 14:10)Alf Onico Wrote: I am not sure if your answer says that there is a doubt about what PDOP is.

It was more about: I cannot tell from memory when a DOP value indicates a good measurement from the GPS device and when to doubt the position that the device records. And if I cannot do that, the vast majority of the RouteConverter users won't be able to do it. So adding a column would bring more questions and no value to the average user.

Is there any means to calculate an accuracy in terms of distance based on any of those DOP values? Is PDOP the only value that you get from your device? I suppose reporting the DOP value is of little value to most of the users as Christian mentioned.

Grüße,
Ilmari
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#6
(02.12.2013, 13:27)IlmariKrebs Wrote: Is there any means to calculate an accuracy in terms of distance based on any of those DOP values?

(02.12.2013, 13:27)IlmariKrebs Wrote: Is PDOP the only value that you get from your device?

The Columbus 9xx, GPX and NMEA formats contain fields for PDOP, HDOP, PDOP but not GDOP or TDOP which would be more interesting if I understand the page that Alf Onico found correctly:
Quote:GDOP : Geometrical Dilution of Precision, (measure of accuracy in 3-D position and time)
PDOP : Position Dilution of Precision (measure of accuracy in 3-D position), also called spherical DOP
HDOP : Horizontal Dilution of Precision (measure of accuracy in 2-D position, for example Latitude and Longitude)
VDOP : Vertical Dilution of Precision (measure of accuracy in 1-D position, Height)
TDOP : Time Dilution of Precision (measure of accuracy in Time)

One could the PDOP values into classes with a descriptive name like the Wikipedia article suggests:
Code:
Value    Rating     
1        Ideal     
1-2      Excellent         
2-5      Good     
5-10     Moderate     
10-20    Fair         
>20      Poor
This page claims rather the same
Quote:A low PDOP is better. A PDOP of 4 to 6 is considered good. Position solutions calculated when the PDOP is from 6 to 10 should be used cautiously because they may have significant error. A PDOP that is above 10 indicates unacceptable error. The ICAO (International Civil Aviation Organization) states that a PDOP of less than 6 is required for en route navigation, with a PDOP of 3 or less required for nonprecision approaches [i.e., not ILS (instrument landing system) types].

So would about having a column "Signal Quality (PDOP)" filled with values "Good (3)", "Moderate (5)", "Ideal (1)"?
--
Christian
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