[Merkaartor] Various GPS issues

[Stefan Dirsch]

On Tue, Aug 18, 2009 at 07:22:50PM +0200, Stefan Dirsch wrote:
> > Maybe there is a conversion error somewhere? The RMC data in the example 
> > has speed in knots and not km/h.
> 
> No, the conversion from knots to km/h is fine (speed in RMC is always in knots
> AFAIK). I double checked that. I was simply wrong with my assumption that the
> speed numbers merkaartor shows are wrong. My fault!

Well, I'm no longer sure what I double checked here. :-( With the NMEA input

 $GPRMC,123646.000,A,4927.196,N,01105.627,E,0.00,0.00,160809,,*01
 $GPRMC,123706.000,A,4918.108,N,01103.959,E,4715.51,186.82,160809,,*39
 $GPRMC,124018.000,A,4918.204,N,01103.947,E,7.25,349.92,160809,,*05
 $GPRMC,124051.000,A,4918.271,N,01103.985,E,13.75,80.76,160809,,*08

merkaartor shows me in debug output

  parsing  O=RMC 1250426206.000 0.005 49.453266667 11.093783333 ? ? ? 0.0000
  0.000 ? ? ? ? 2 * 
  parsing  O=RMC 1250426226.000 0.005 49.301800000 11.065983333 ? ? ? 186.8200
  2425.868 ? ? ? ? 2 * 
  parsing  O=RMC 1250426418.000 0.005 49.303400000 11.065783333 ? ? ? 349.9200
  3.730 ? ? ? ? 2 * 
  parsing  O=RMC 1250426451.000 0.005 49.304516667 11.066416667 ? ? ? 80.7600
  7.074 ? ? ? ? 2 * 

and as values in km/h in the GUI exactly these numbers, i.e.

  0 km/h
  2425.87 km/h
  3.73 km/h
  7.074 km/h

Isn't one knot 1,852 km/h? Looks like values are shown in meter/second instead
of km/h.

  4715.51 * 1.852 / 3.6 = 2425.87
  7.25 * 1.852 / 3.6 = 3.73
  13.75 * 1.852 / 3.6 = 7.074

Makes sense?

Best regards,
Stefan

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Stefan Dirsch (Res. & Dev.)   SUSE LINUX Products GmbH
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