NMEA Sentences / Parameters , which to choose for OSM GPX file ? (RMC, GGA)

Question

Hello all :)

I have an Qstarz antenna, and with the utility, i can choose what the antenna provide to me. I have Choose RMC and GGA ( http://www.gpsinformation.org/dale/nmea.htm )...but, i can add 6 parameters.

In OpenStreetMap, what are the sentences that are important in the Nmea log ?

Thanks ;)

Accepted Answer

I addition to the already suggested lat, long and timestamp I would recommend you to provide HDOP, the Horizontal Dilution Of Precision. HDOP is used by the JOSM editor when the option "Draw a circle from HDOP value" is enabled. That's a nice tool to judge the quality of the trace. You'll get the HDOP from the GGA sentence.

It's also possible to use the gpsbabel command to wash the gps traces and remove points with too high HDOP. The gpsbabel command can filter by other quality parameters as well, but HDOP is probably the most important one since OSM is (almost) 2D.

Answer 2

3

Just in case you haven't seen it, you've had a read of http://wiki.openstreetmap.org/wiki/NMEA already presumably? That makes some recommendations (and there's a link from there about converting to gpx using e.g. gpsbabel).

If you have seen that page already, and wanted to ask what people generally use when extracting NMEA data, then the silence here probably suggests that not many people are actually doing it. If you're asking because the wiki page or linked information seems incomplete or wrong I'd update it.

permanent link

answered 16 Feb '11, 02:27

SomeoneElse ♦
36.9k●71●370●866
accept rate: 16%

Yes, i have found this page previously...but, it's a explain of the Nmea trame, not the choice of parameters accepted by the OSM.

The GPX format can contain all parameters of a Nmea trame...so, it's why i ask this question.

I will not provide HDOP or PDOP if it is useless to OSM ... I can use the bandwidth for other parameters and keep GPX less fat in the end (just benefit to OSM).

The thinks is that the Nmea trame is very "commun" with an bluetooth antenna (and a Windows Mobile application)...

With 1Hz, the GPX application are ok...but i produce 5Hz or 10Hz with my personal configuration.

(16 Feb '11, 20:01) RGPS

Well, GPX traces are just a means to an end, as far as OSM is concerned. They just enable you (and other people who see your traces as a background in editors) to add features to the map. I'm sure that you've already found what OSM needs in a GPX trace to allow you to upload it (lat, long, some sort of timestamp). The answer to what would be useful is - whatever you want, but it doesn't have to be much more than that.

(16 Feb '11, 23:13) SomeoneElse ♦

Answer 3

OK...thanks to all, so i have choose (note: on Qstarz antenna, you can not use only GGA, you must have RMC...but the bandwidth don't use "clone" data...) :

RMC
----------
 RMC          Recommended Minimum sentence C
     123519       Fix taken at 12:35:19 UTC
     A            Status A=active or V=Void.
     4807.038,N   Latitude 48 deg 07.038' N
     01131.000,E  Longitude 11 deg 31.000' E
     022.4        Speed over the ground in knots
     084.4        Track angle in degrees True
     230394       Date - 23rd of March 1994
     003.1,W      Magnetic Variation
     *6A          The checksum data, always begins with *
----------

GGA
----------
GGA          Global Positioning System Fix Data
     123519       Fix taken at 12:35:19 UTC
     4807.038,N   Latitude 48 deg 07.038' N
     01131.000,E  Longitude 11 deg 31.000' E
     1            Fix quality: 0 = invalid
                               1 = GPS fix (SPS)
                               2 = DGPS fix
                               3 = PPS fix
                   4 = Real Time Kinematic
                   5 = Float RTK
                               6 = estimated (dead reckoning) (2.3 feature)
                   7 = Manual input mode
                   8 = Simulation mode
     08           Number of satellites being tracked
     0.9          Horizontal dilution of position
     545.4,M      Altitude, Meters, above mean sea level
     46.9,M       Height of geoid (mean sea level) above WGS84
                      ellipsoid
     (empty field) time in seconds since last DGPS update
     (empty field) DGPS station ID number
     *47          the checksum data, always begins with *
----------

and, for me (optional parameters fit in the 10Hz bluetooth bandwidth on Windows Mobile 6)

GSA
----------
 GSA      Satellite status
     A        Auto selection of 2D or 3D fix (M = manual) 
     3        3D fix - values include: 1 = no fix
                                       2 = 2D fix
                                       3 = 3D fix
     04,05... PRNs of satellites used for fix (space for 12) 
     2.5      PDOP (dilution of precision) 
     1.3      Horizontal dilution of precision (HDOP) 
     2.1      Vertical dilution of precision (VDOP)
     *39      the checksum data, always begins with *
----------

VTG
----------
 VTG          Track made good and ground speed
        054.7,T      True track made good (degrees)
        034.4,M      Magnetic track made good
        005.5,N      Ground speed, knots
        010.2,K      Ground speed, Kilometers per hour
        *48          Checksum
----------

NMEA Sentences / Parameters , which to choose for OSM GPX file ? (RMC, GGA)

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