Re: [gpsd-users] Position accuracy of AIS data in gpsd json?

[Gary E. Miller]

Yo Sven!

gpsd output a ton of different variables.  Which ones specifically
do you think need more digits?

On Fri, 10 Aug 2018 10:40:35 +0200
Sven Geggus <address@hidden> wrote:

> Gary E. Miller schrieb am Friday, den 10. August um 00:37 Uhr:
> 
> > Lost me.  By citation I mean an external specification we can comply
> > to.  And I have no idea which feilds you are concerned about.  
> 
> OK, I will try to explain this from scratch.
> 
> On a gpsd client I can either request the data in scaled or unscaled
> mode.
> 
> When using the latter I get longitude and latitude in minutes/10000
> regarding the decription at:
> 
> http://catb.org/gpsd/AIVDM.html#_types_1_2_and_3_position_report_class_a
> 
> Regardless of any real world GPS accuracy minutes/10000 corresponds
> to a resolution of 1/600000.0 degrees thus 6 decimal places are
> needed to express this resolution.
> 
> Now when choosing scaled mode I will get 4 decimal places (%.4f in
> gpsd_json.c) thus this resolution is truncated.
> 
> Unfortunately this is even below the resolution of a GPS device which
> would need %.5f IMO.  However I still think that it should be up to
> the client to interpret the accuracy of the result and would expect
> the digits to represent the full NMEA resolution rather than a random
> decision made in the server code.
> 
> This said, it will not matter that much to me as I can change my
> client to use unscaled mode and scale the data myself.
> 
> Regards
> 
> Sven
> 




RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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