green ball or green bars?

[r.van.kasteel]

What is better for OpenCPN with AIS data overlay: a green ball or green bars in the top right corner? And why? This is what the manual says:


"The status icons should be interpreted as follows:

red ball: No GPS data at all, or position not available.

green ball: GPS position available, and good for navigation

1 green vertical bar: Active/Valid GPS data + GPS reporting 1 - 4 satellites, if available from GPS receiver.

2 green vertical bars: Active/Valid GPS data + GPS reporting 5 - 9 satellites, if available from GPS receiver.

3 green vertical bars: Active/Valid GPS data + GPS reporting 10+ satellites, if available from GPS receiver."

[nohal]

They are exactly the same, the ball just means we get the position often enough, but we don't know how many satellites provide the position, for example when we get the data filtered over a network and not directly from a GPS.

[rgleason]

I'd want 3 green bars

[bcn]

I'd want 3 green bars

This depends -

five sats with a strong signal can give a better fix than ten at low elevation pinned on the horizon.
Some modern designs of GPS chip sets disregard "low quality" sats and rely on few ones with optimal reception.

What they will show in the GSV NMEA sentence - all sats in sight or just the ones used - is another story.

[r.van.kasteel]

thanks for your answers, but to be honest: I still don't know the differences. Is there a more "scientific" explanation? A fellow sailor says that a green ball is not good enough and one should always opt for three vertical green bars...

[bcn]

Originally Posted by nohal

They are exactly the same, the ball just means we get the position often enough, but we don't know how many satellites provide the position, for example when we get the data filtered over a network and not directly from a GPS.

Green Ball: there is a fix, the position is known and received from the GPS
Bars: the GPS sends as well the data about the satellite constellations (its name/the PRN, azimuth and elevation for each of the sats - used for drawing then at the dashboard)

If there are a lot of fluctuations in the presentation of the bars, there might be problem with the reception but there is no direct relation like many satellites=good quality. It is more probable that the fix, the result, is better but no guarantee. And with more satellites the reception is more stable too.
Interesting in urban environments, but for boating a minor issue in general.

You can access to the estimate of error of the GPS unit, but really, if there is fix for navigation purposes it should be ok but in very strange circumstances.

If you want to work with autonomous vessels (automatic docking) and centimeter precision then all this is getting a tad more complicated...

[rgleason]

Added portions of this discussion to the Wiki page
https://opencpn.org/wiki/dokuwiki/do...tup_and_status

Feel free to edit if you are an editor.

[bcn]

Rick,

perhaps one point to add:

A GPS fix requires a minimum of 4 satellites to resolve the four unknowns
X,Y,Z (spatial) and t (time)

Showing only one bar - 1-4 sats - the reception will not be very stable most probably.

Hubert

[yachtvalhalla]

Originally Posted by r.van.kasteel

A fellow sailor says that a green ball is not good enough and one should always opt for three vertical green bars...

Your fellow sailor evidently doesn't know what the green ball means. As explained earlier, it means the GPS signal is not coming directly from the GPS (with it's additional collateral information) but from elsewhere, such as via an AIS device or network. At least that's my understanding.

Terry

[rgleason]

Obviously, we would like to have "green ball" description correct.

GPS fix, the position is known and received from the GPS. Signal is frequent enough for navigation, satellite count is not available in the data feed.

Pavel: "They are exactly the same, the ball just means we get the position often enough, but we don't know how many satellites provide the position"

bcn: A GPS fix requires a minimum of 4 satellites to resolve the four unknowns
X,Y,Z (spatial) and t (time). Showing only one bar - 1-4 sats - the reception will not be very stable most probably.

Terry: As explained earlier, it means the GPS signal is not coming directly from the GPS (with it's additional collateral information) but from elsewhere, such as via an AIS device or network. At least that's my understanding.

Terry this is new to me... what should it be?

[yachtvalhalla]

Originally Posted by rgleason

Terry this is new to me... what should it be?

It is what it is. I'm comfortable with seeing the green ball when the GPS signal is multiplexed with the AIS signal (at 38400 bps). I feed the GPS signal from my Furuno GP-32 unit (at 4800 bps) into the AIS unit. I have confidence in the origin of the GPS signal. If the green ball disappears I know I have a connection problem (has never happened) or have lost GPS coverage (which has happened once or twice) in which case I get an alert from the Furuno.

Terry

[bcn]

Terry,

Green Ball: there are no GSV message about the single sats yet, but there is a fix.

When starting up OpenCPN you will see first the Green Ball as there are some messages with valid GPS data coming in - directly or via network, multiplexed or
not.

Next, when the GSV messages drop in, the Bars will show up.

If your network or multiplex filters the GSV sentences out, the only indicator will be the Green Ball.

Hubert

[rgleason]

OK, How is this now?
GPS Setup and Status

If it is too wordy, please suggest improvements.
Thank you.

[r.van.kasteel]

Wow, thank you all for your input.
As far as I understand it now: three bars or a green ball are the same and I don't have to bother if I see 3 bars or a green ball :-)

[nohal]

Not exactly. The green ball is the same as 3 bars, 2 bars or 1 bar.
The ball means that we do not know how many satellites are in sight = we dont' know how many bars we should draw. But again, that you see the ball, not the bars, has nothing to do with the actual position accuracy.

But you don't have to worry, if your GPS antenna has clear visibility of the sky, it is highly unlikely you don't see enough sats to get quality position.