Beta Test / Technical

[bcn]

Thomas,

can you try to catch the NMEA stream?
Depending on the reception quality and the internal filter of the GPS noise can appear as speed.

Hubert

[cagney]

Originally Posted by bcn

Thomas,

can you try to catch the NMEA stream?
Depending on the reception quality and the internal filter of the GPS noise can appear as speed.

Hubert

Hubert
Will do, but it will take a while before we're in a similar situation again.
Staying anchored for awhile due to boat work.
Thomas

[CarCode]

Originally Posted by cagney

Hubert
Will do, but it will take a while before we're in a similar situation again.
Staying anchored for awhile due to boat work.
Thomas

I see things like this when only a few sats are in view and only 3-4 sats are in use by OpenCPN. Try to add the items to the Dashboard as seen in the attachment. That helps to estimate the fix quality.

Gerhard

[bcn]

The number of satellites in use does not depend from OpenCPN.

Depending on the quality (estimation) of the internal filters of the GPS will discard satellites which do not increase the quality of the solution.
For example such with a low elevation.
4 good satellites are sufficient for a fix. More usable Sats will increase the stability of the solution/fix.

[CarCode]

Originally Posted by bcn

The number of satellites in use does not depend from OpenCPN.

Depending on the quality (estimation) of the internal filters of the GPS will discard satellites which do not increase the quality of the solution.
For example such with a low elevation.
4 good satellites are sufficient for a fix. More usable Sats will increase the stability of the solution/fix.

Exactly what I said and therefore activate the items shown above in Dashboard to see what is going on...

Gerhard

[Douwe Fokkema]

Originally Posted by cagney

Attachment 139749

Look at this...! We have been anchored for hours. Very stable at anchor no swinging back and forth and no surge. Still O shows us doing 1.0 kts? I have observed this a couple of times the last few days. Unplugging & reconnecting the USB/GPS plug sets things right again.
Using 4.5 latest Git. Ubuntu 14.04

/Thomas

OpenCPN just takes the COG as it is presented by the GPS. So the "fault" is in the GPS. However OCPN can filter the COG values. This filtering is an averaging of the absolute values of the COG presented by the GPS. So if you would go round in small circles with a speed of 1 kn the average will be 1kn. An alternative way of filtering could be not to filter the absolute values of COG but consider COG as a vector and take the average of this vector over time. One would then average the latitude component and the longitude component of COG separately and find from both averages values the average COG and SOG. Going round in small circles again with a speed of 1 kn, now the average COG would be 0.
I could do a trial implementation of this, but would need a test gpx file and my boat is laid up now.

Douwe Fokkema

[CarCode]

Originally Posted by Douwe Fokkema

OpenCPN just takes the COG as it is presented by the GPS. So the "fault" is in the GPS. However OCPN can filter the COG values. This filtering is an averaging of the absolute values of the COG presented by the GPS. So if you would go round in small circles with a speed of 1 kn the average will be 1kn. An alternative way of filtering could be not to filter the absolute values of COG but consider COG as a vector and take the average of this vector over time. One would then average the latitude component and the longitude component of COG separately and find from both averages values the average COG and SOG. Going round in small circles again with a speed of 1 kn, now the average COG would be 0.
I could do a trial implementation of this, but would need a test gpx file and my boat is laid up now.

Douwe Fokkema

I guess the far better solution is to have a better GPS device. There are devices available with an accuracy of up to 2-3 centimeter. It is always a question how much money to invest...

Gerhard

[bcn]

Even quite expensive multifrequency band GPS receivers with external differential corrections will show some noise. Overkill for a pleasure craft anyhow.

Douwe's idea should work quite well for SOG.

[cagney]

I have recorded a VDR file of a similar situation. Anchoring and O 4.5.0 continues to show some speed.
I 'm using an old Garmin GPS 128, that shows 7 good satellites used.

O shows: COG 121, SOG 0.9
GPS128 shows: COG 121, SOG 0.0

redshank.txt.pdf

Thomas

[bcn]

Interesting indeed.

$GPRTE,1,1,c,0*07
$GPRMC,190900,A,2328.518,N,07543.911,W,000.0,121.2,210117,007.8,W*77
$GPRMB,A,,,,,,,,,,,,V*71
$GPGGA,190900,2328.518,N,07543.911,W,1,10,0.9,10.1,M,-34.0,M,,*48
$GPGSA,A,3,01,10,12,14,18,22,25,26,31,32,,,1.5,0.9,1.2*33
$GPGSV,3,1,10,01,07,305,36,10,66,152,49,12,12,041,41,14,45,338,47*7A
$GPGSV,3,2,10,18,35,147,44,22,05,319,31,25,46,068,46,26,25,190,43*7D
$GPGSV,3,3,10,31,60,282,47,32,52,019,48,,,,,,,,*75
$PGRME,3.5,M,4.6,M,5.8,M*27
$GPGLL,2328.518,N,07543.911,W,190901,A*33
!AIVDM,1,1,,B,H5NOCc0EQ05A8T5@D0000000000,2*46
$PGRMZ,33,f,3*2B
!AIVDM,1,1,,B,H5NOCc4TFC@<BI;G47jkjp0`6220,0*59
$PGRMM,WGS 84*06
$GPBOD,,T,,M,,*47
$GPRTE,1,1,c,0*07

The only sentence that carries SOG/Velocity is the RMC one. And this shows 000.0
All the time...
So, where comes the speed from?? Different with 4.4 ?

[Douwe Fokkema]

I tested the redshank.txt with 4.2, an older 4.5 (0fe5f55e0f7b14) and the latest 4.5. First 2 versions give a nice SOG of 0.0 and a COG of 121, without filtering. This is as it should be apart from the COG, GPS seems to do the filtering as it presents a SOG of 0. all the time. But the last version (02c0061f6) shows a SOG of --- in the bottom line. In this case SOG is valid but 0., consequently COG is not valid, though it is presented by the GPS. So various options are possible:
- consider both COG and SOG as not valid if SOG is absent or 0. (current situation)
- always present COG an SOG if and as received from the GPS
- allow for a valid SOG with an invalid COG where we make COG invalid if SOG < .01 (some limit)
The last option may be the nicest but adds complexity, the second option seems sufficient to me (change m_NMEA0183.Rmc.SpeedOverGroundKnots > 0 into m_NMEA0183.Rmc.SpeedOverGroundKnots >= -0. )

With the redshank.txt I have not seen the fluctuating SOG that started this discussion.

Douwe Fokkema

[dominig]

Hello,

I am afraid that the link for OpenSUSE has gone wrong again with the new Web design.
The link points on my test building page while it was corrected a few month ago to point on the OpenSUSE wiki page which follows system update and gives the correct links.

Could that link be reverted to the right value ?

https://fr.opensuse.org/OpenCPN

Dominig

[Rasbats]

Now corrected. Let me know if you see any errors.

Mike

[cagney]

Dave
Testing 4.5.0, Git up to date.
Options->Display->Units
The options "Show True bearings and headings" and "Show magnetic bearings and heading", can both be ticked at the same time??

Also the text for using magnetic bearings is a bit jumbled.
No clear distinction between WMM and the manual option.

Thomas

[bdbcat]

cagney...

We can now show BOTH true and mag bearings if desired, for example on a route segment rollover popup. Try it.

Do you have a suggestion for improvement on the text?

Dave