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Old 22-09-2020, 23:00   #1
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Bug ? OpenCPN sees a FIX, while GPS data are not consistent

Hello girls and guys!

- On cold starts I experience many apparent freeze of OpenCPN !
(CPU occupancy 25%, which means 1 core is 100% occupied ).

- The display indicates a FIX is acquired, though GNSS data are still not consistent (See picture). This looks like a bug ...

- Display can also be quite crazy, if the 'center boat on screen' function was activated !

- After a period, GPS data stabilizes and everything gets OK, which means it was not a deadly FREEZE !

- On a warm start, GPS data are almost immediately consistent,
and the bug doesn't show off !

The config. used : RPi4-8GB, Openplotter 2.4.1 stable, OpenCPN 5.2.0.9,
GNSS input signal connected to Signal K


BTW : Many thanks to both dev teams (Openplotter and OpenCPN) for the fantastic job !
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Old 22-09-2020, 23:31   #2
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Re: Bug ? OpenCPN sees a FIX, while GPS data are not consistent

pls describe "cold" vs "warm" start - are you referring to the temperature of the raspi?
(indeed a gps chip may need to warmup to produce relaible readings - same even more so with sdr chips)
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Old 23-09-2020, 02:30   #3
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Re: Bug ? OpenCPN sees a FIX, while GPS data are not consistent

Quote:
Originally Posted by skipperearly View Post
pls describe "cold" vs "warm" start - are you referring to the temperature of the raspi?
(indeed a gps chip may need to warmup to produce relaible readings - same even more so with sdr chips)

No I am referring to the GNSS USB mouse. When cold (i.e.not powered for a long duration these small peripherals loose data ( Almanach, etc) which requires at next (cold) start-up a sensible delay to establish a FIX and deliver a consistent position. Once fully operative they can keep such data for say one day or more (warm start up).
The issue there is than when using Signal K connection, OCPN get confused and believe it has a FIX, when position data are still not reliable !
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Old 25-09-2020, 09:49   #4
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Re: Bug ? OpenCPN sees a FIX, while GPS data are not consistent

Quote:
Originally Posted by Didier B View Post
..........
The issue there is than when using Signal K connection, OCPN get confused and believe it has a FIX, when position data are still not reliable !
Didier..
There was before similar issues when connected to Signal K. Historical data was received upon connection and was shown until updated. With O 5.2 and latest Signal K this was solved for other type of data. What's your Signal K version? If older than 1.31, if I remember correct, it may be the cause. Recent version is 1.33
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Old 26-09-2020, 08:26   #5
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Re: Bug ? OpenCPN sees a FIX, while GPS data are not consistent

I have do say SK version in OP was 1.26 until this morning when it was upgraded to 1.34 ... and it seems the loonnng wait for a real FIX is simply gone
Now, position data are consistent from start up, and (real) FIX condition is reached almost immediately .


Another big thank you to both dev. teams for solving the point !
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Old 29-09-2020, 05:58   #6
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Re: Bug ? OpenCPN sees a FIX, while GPS data are not consistent

Updating signal k server does not fix this issue. Do this to reproduce it:


Cover the GPS antenna with a metallic plate to force a satellite signal lost, then signal k data for position becomes:

{
"longitude": null,
"latitude": null
}

OpenCPN is not managing this ok. The expected behavior would be to keep the last know position before losing satellites but currently OpenCPN is placing the boat in lat 0, lon 0 or any erratic position.

could this be related to the position prediction algorithm?
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Old 29-09-2020, 10:05   #7
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Re: Bug ? OpenCPN sees a FIX, while GPS data are not consistent

Saillog..
Since you seem to having seen this:

The reported lat and long is a JSON string that we transform to a double. Is the value "null" or how is this reported for the position path? Is your text "null" above from e.g. SK Data browser? If so it would be feasible to use the method "IsDouble()"

This is an example from my SK Data browser:

navigation.position
{
"longitude": 11.622725,
"latitude": 57.63847
}
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Old 29-09-2020, 11:39   #8
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Re: Bug ? OpenCPN sees a FIX, while GPS data are not consistent

Hi Hakan,


when I have a fix I have the same signal k position value than you (obviously with my coordinates):


navigation.position
{
"longitude": 11.622725,
"latitude": 57.63847
}



but when I force the lost position signal k sends a null value. This null value is neither text nor a number, is the json value for "void" or "none". Yes, this is what I get in signal k data browser:


navigation.position
{
"longitude": null,
"latitude": null
}


sorry I am not familiarized with the opencpn code and I do not understand that "double" concepts
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Old 29-09-2020, 11:48   #9
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Re: Bug ? OpenCPN sees a FIX, while GPS data are not consistent

Sailoog..
Thanks for this test result. Then I've a suggest to solve this. Let's see if it pass our bellowed main developer.
Hĺkan
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Old 30-09-2020, 06:02   #10
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Re: Bug ? OpenCPN sees a FIX, while GPS data are not consistent

Hĺkan


I really appreciate that.

It is quite annoying and it could even be dangerous.
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