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Position accuracy

Giorgio Moscardi
Hi,

as I have already mentioned some time ago, I have built my own GPS
logger with the Arduino platform, which produces unicsv files. I then
process the created files with gpsbabel to turn them into GPX. It
works well enough for my needs.

Now I would like to add the possibility of recording position accuracy
data, which I receive through the $GPGST NMEA sentence, but I can't
see any suitable field in the unicsv description page to put such an
information in. Any hints? Can I just add my own fields? Will gpsbabel
just ignore then?

Also, does GPX provide any fields for this?

Thanks,
G.

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Re: Position accuracy

Robert Lipe-4


On Sat, May 6, 2017 at 5:43 PM, Giorgio Moscardi <[hidden email]> wrote:
Hi,

as I have already mentioned some time ago, I have built my own GPS
logger with the Arduino platform, which produces unicsv files. I then
process the created files with gpsbabel to turn them into GPX. It
works well enough for my needs.

Now I would like to add the possibility of recording position accuracy
data, which I receive through the $GPGST NMEA sentence, but I can't
see any suitable field in the unicsv description page to put such an
information in. Any hints?

We don't parse GPGST as it's out of bounds for the types of data this project focuses on. Adding it to our NMEA parser would be pretty mechanical if you have only one GPS type that you care about.
 
Can I just add my own fields? Will gpsbabel
just ignore then?

You have the source. You're welcome to add anything you like.

 
Also, does GPX provide any fields for this?

Not really, because it's not really a concept that ports well between devices and formats which (like ours) is the point of that format. If  you're just looking for a field to smuggle it in, you could use the dilution of precision members. That's already in our unicsv handler. It'd be easier than creating an gx:extension.

http://www.topografix.com/gpx/1/1/gpx.xsd 

If you control all the software involved and not really interested in interchange like we are, you could put it in heart rate or crank cadence or lots of other square holes.

RJL

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Re: Position accuracy

Craig Bergh
Hello Giorgio,
Would a gps file of sbp or sbp type include positional data? Can the horizontal dilution is precision (HDOP) be determined? I document HDOP in my GPS project as a measure of accuracy. Is this a solution?
Craig Bergh

Sent from my iPhone

On May 6, 2017, at 8:48 PM, Robert Lipe <[hidden email]> wrote:



On Sat, May 6, 2017 at 5:43 PM, Giorgio Moscardi <[hidden email]> wrote:
Hi,

as I have already mentioned some time ago, I have built my own GPS
logger with the Arduino platform, which produces unicsv files. I then
process the created files with gpsbabel to turn them into GPX. It
works well enough for my needs.

Now I would like to add the possibility of recording position accuracy
data, which I receive through the $GPGST NMEA sentence, but I can't
see any suitable field in the unicsv description page to put such an
information in. Any hints?

We don't parse GPGST as it's out of bounds for the types of data this project focuses on. Adding it to our NMEA parser would be pretty mechanical if you have only one GPS type that you care about.
 
Can I just add my own fields? Will gpsbabel
just ignore then?

You have the source. You're welcome to add anything you like.

 
Also, does GPX provide any fields for this?

Not really, because it's not really a concept that ports well between devices and formats which (like ours) is the point of that format. If  you're just looking for a field to smuggle it in, you could use the dilution of precision members. That's already in our unicsv handler. It'd be easier than creating an gx:extension.

http://www.topografix.com/gpx/1/1/gpx.xsd 

If you control all the software involved and not really interested in interchange like we are, you could put it in heart rate or crank cadence or lots of other square holes.

RJL
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Re: Position accuracy

Giorgio Moscardi
2017-05-07 19:06 GMT+02:00 Craig Bergh <[hidden email]>:
> Would a gps file of sbp or sbp type include positional data? Can the
> horizontal dilution is precision (HDOP) be determined? I document HDOP in my
> GPS project as a measure of accuracy. Is this a solution?

I don't even know what an sbp file is :). I'm not really a GPS-guru,
but I seem to understand that H/V/PDOP are not really a measure of
accuracy, but rather of how satellite positions affect it. It is
dimensionless, while I would need something that can be transformed
into a length, so that I can draw an ellipse of uncertainty.

$GPGST is supported by my GPS and reports the standard deviation of
the measurment in the three dimensions, so it seems to suit my needs
perfectly.

Thanks anyway,
G.

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Fwd: Position accuracy

Giorgio Moscardi
In reply to this post by Robert Lipe-4
2017-05-07 3:48 GMT+02:00 Robert Lipe <[hidden email]>:
> We don't parse GPGST as it's out of bounds for the types of data this
> project focuses on. Adding it to our NMEA parser would be pretty mechanical
> if you have only one GPS type that you care about.

I never asked for support for $GPGST in gpsbabel. I do my own parsing
right on Arduino and produce a unicsv file, so all I was asking about
is whether the unicsv format provides any fields for this purpose.


>> Also, does GPX provide any fields for this?
>
>
> Not really, because it's not really a concept that ports well between
> devices and formats which (like ours) is the point of that format.

I see, but I reckon that position accuracy has its importance when you
are recording a GPS track, in case you want to post-process it somehow
later.

Thanks anyway,
G.

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