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Re: [gpsd-users] Position accuracy of AIS data in gpsd json?
From: |
Sven Geggus |
Subject: |
Re: [gpsd-users] Position accuracy of AIS data in gpsd json? |
Date: |
Fri, 10 Aug 2018 10:40:34 +0200 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
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
--
"Der wichtigste Aspekt, den Sie vor der Entscheidung für ein Open
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/me is address@hidden, http://sven.gegg.us/ on the Web
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- [gpsd-users] Position accuracy of AIS data in gpsd json?, Sven Geggus, 2018/08/09
- Re: [gpsd-users] Position accuracy of AIS data in gpsd json?, Gary E. Miller, 2018/08/09
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- Re: [gpsd-users] Position accuracy of AIS data in gpsd json?, Gary E. Miller, 2018/08/09
- Re: [gpsd-users] Position accuracy of AIS data in gpsd json?,
Sven Geggus <=
- Re: [gpsd-users] Position accuracy of AIS data in gpsd json?, Gary E. Miller, 2018/08/10
- Re: [gpsd-users] Position accuracy of AIS data in gpsd json?, Sven Geggus, 2018/08/11
- Re: [gpsd-users] Position accuracy of AIS data in gpsd json?, Gary E. Miller, 2018/08/11
- Re: [gpsd-users] Position accuracy of AIS data in gpsd json?, Sven Geggus, 2018/08/11
- Re: [gpsd-users] Position accuracy of AIS data in gpsd json?, Gary E. Miller, 2018/08/11