Quote:
Originally Posted by cagney
Can you give a summary of the meaning of
the red and green diamond targets and the green target with a "diamond"-stern
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Thomas,
The diamond targets are displays of
NMEA CDDSC/CDDSE sentences. This is what NMEA-output-capable
DSC VHF is passing to a
chartplotter upon receiving a
DSC Distress Alert or a DSC Position Report, e.g. in response to a previous Position
Poll. The supplied patch interprets only some of the fields of the sentence, extracting the position, sender MMSI and message format that gets categorized as
Distress or - in all other cases - as Position Reports. So when your suitably connected
VHF beeps and calls for attention, you will hopefully have a diamond on the chart in the proper position, red for distress, green for other position reports.
This is not meant as replacement for any of the GMDSS procedures, but may provide a help and a quick cross-check.
The diamonds behave similarly to
AIS targets, appearing in AIS target list, displaying summaries on mouse rollover and showing reasonable properties. If needed, the user can drop a mark on them or select a "go to here" etc.
If AIS target ageing is enabled, they will go away in time.
The example shown near Tokyo comes from the Uniden UM415 Owners Manual:
$CDDSC,12,3081234000,,07,00,0354013946,0657,,,S,E* 6D
$CDDSE,1,1,A,3081234000,00,60875646*13
CDDSC gives the format, MMSI and position down to whole minutes
CDDSE extends for this MMSI the precision by 4 fractional digits
In full generality there can be a lot more of various fields and a lot more information, but for Distress and Position Report this should work well and be useful.
The targets with diamond sterns are displayed upon receiving a position report in the GPSGate Server Protocol, i.e. a $FRPOS sentence. Such sentences are sent by GPSGate Server in response to a request for Buddy List positions. GPSGate is not marine-specific (in the example shown the "Johan" is probably a truck) but it is increasingly popular for
tracking many different vehicles reporting their positions by various
communications means, often using cellular phones. The example shown is
$FRPOS,6311.64120,N,01438.02740,E,0.0,0.000,0.0,27 0707,154403.000,Johan*18
A Buddy Group could well be a
charter flotilla or a fleet of inshore sea-rescue vessels.
Some
marine chartplotters e.g. SOBvMAX include GPSGate Buddy
tracking as standard.
The patch submitted does not implement the communication with a GPSGate Server, so it is not a complete solution, but rather a first step towards it. If needed, I am prepared either to write a small client program or to look for existing
software that would produce the $FRPOS stream for OpenCPN.
I think the priority for including any of this in production OpenCPN is low, so it is perhaps too early to include pictures in the
documentation but it may well change in near future...
So, if there is anyone out there who does manage a GPSGate Buddy Group or has a suitable DSC VHF and is willing to try or develop this further, the first step is done...
Piotr