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
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 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
A Buddy Group could well be a charter
flotilla or a fleet of inshore sea-rescue vessels.
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...