OCPN support VHF DSC Position NMEA sentences?

[Gypsy23]

Originally Posted by NahanniV

Off topic, but thought I would bring it up while people are testing.

Is any of the equipment being tested here capable of setting up a DSC call over NMEA0183 ?

Can this be documented so that functionality can eventually be added to OpenCPN ?

Cheers,
JM.

I have only been testing how OCPN and RM E120W handle the incoming DSC calls. I have a VHF DSC Class D radio from which I have captured the data but all calls I make to get an 'Auto Position Reply' have come from manual entry. In fact my radio makes no mention of accepting NMEA 0183 msgs to initiate a call. Perhaps more sophisticated radios have that feature.

[stevead]

I have been successfully "controlling" my Icom M504 VHF DSC radio with NMEA DSC sentences with my own software. I can successfully initiate Individual, Group, Poll & Position requests.

I have not attempted DSC Distress Alerts, Urgency or Safety messages, because of the potential consequences ! Should really try and find a training centre with interconnected radios that are not connected to antennas !

If I remember correctly I logged a request in Flyspray with outlining the NMEA DSC sentence format that operates with my Icom M504. Not sure what other brands of radios correctly adhere to the NMEA DSC sentence format.

May also attempt the same with a MF/HF radio to see if I can code the MF/HF frequencies correctly in the NMEA DSC Sentence.

[rgleason]

stevead,
Control of your DSC radio with Nmea with your computer. I wonder if this was intended? It is very interesting, because in some ways control by software has potential to be a lot clearer and easier.

[PjotrC]

Originally Posted by Gypsy23

I will generate a request for a change in Flyspray.

Ray,

I have posted #FS1719, "Allow any C class talker to send DSCDSE". It seems about a two-keystroke change, so maybe some maintenance release will allow you to test your set directly with OCPN soon. Your feedback is very useful, so let's hope for a kind soul to make this happen ...

Or did I miss your posting there?

Piotr

[rgleason]

FS#1719 - AIS - VHF/DSC Allow any C class talker to send DSCDSE
FS#1719 : AIS - VHF/DSC Allow any C class talker to send DSCDSE

This was under the Grib_pi project. I moved it to the OpenCPN New Features project. I hope that is appropriate now.

[Gypsy23]

Originally Posted by PjotrC

Ray,

I have posted #FS1719, "Allow any C class talker to send DSCDSE". It seems about a two-keystroke change, so maybe some maintenance release will allow you to test your set directly with OCPN soon. Your feedback is very useful, so let's hope for a kind soul to make this happen ...

Or did I miss your posting there?

Piotr

Hi Piotr
Thanks for your follow-up and listing on FlySpray.
I did list on 10Jan15 #1703 "Allow different Talker IDs for DSC/DSE NMEA0183 messages". Maybe it got bumped down the list so you didn't see it. It got assigned to Dave.

I guess someone can 'marry' these requests. Mine has a description of the requirement, yours has a proposed solution.

Cheers
Ray

[rgleason]

Married #1703 (copied all #1719 into #1703)
FS#1703 : AIS - VHF/DSC Allow different Talker IDs for DSC/DSE NMEA0183 messages

Closed #1719 Now a duplicate.

[RhythmDoctor]

Originally Posted by continuouswave

I already extracted the payload. I just want to let you know how much of a chore you made it.

That "chore" is necessary to get the website to accept the upload. The message board software will only accept certain file types, and severely limits the size of some types. PDF files can be larger than the others. Try uploading a log file sometime and you'll see why it's done this way.

Personally, I never found deleting four characters of text from the filename to be much of a chore.

[RhythmDoctor]

Originally Posted by Gypsy23

I have only been testing how OCPN and RM E120W handle the incoming DSC calls. I have a VHF DSC Class D radio from which I have captured the data but all calls I make to get an 'Auto Position Reply' have come from manual entry. In fact my radio makes no mention of accepting NMEA 0183 msgs to initiate a call. Perhaps more sophisticated radios have that feature.

I agree. Can someone suggest any radio that accepts DSC sentences? I know that the popular Standard Horizon ones do not.

It's easy to tell for NMEA 0183 radios - just go to the wiring information in the manual and look to see if there is a DSC input.

Until there is a radio that takes DSC input, there isn't much reason to build that capability into OpenCPN.

[rgleason]

Thanks guys for the Tracker task. I get RDr point but if it is not too much programming perhaps its worthwhile.

I believe you have all moved VHF/DSC, testing and knowledge well beyond this writeup:

DSC and Buddy via AIS. | Official OpenCPN Homepage

It seems to me that the
http://www.cruisersforum.com/forums/...ml#post1761942 Writeup for

"When connecting a DSC radio to OCPN users would benefit greatly from checking the manufacturers specs, and trying out a few scenarios, to get a feeling of how they are handled. Clearly, this is not the same support as expected from a typical Class D equipment. .. recommend again the steps suggested a little earlier in this thread ( OCPN support VHF DSC Position NMEA sentences? ), plus

5. excluding the DSC targets (especially Distress) from distance filtering in the AIS Target List.

http://www.cruisersforum.com/forums/...ml#post1735151


Table of Results
http://www.cruisersforum.com/forums/...ml#post1762655

-------
Can someone who knows this subject intimately check and update the wiki?
Thanks so much.

[Gypsy23]

Originally Posted by RhythmDoctor

I agree. Can someone suggest any radio that accepts DSC sentences? I know that the popular Standard Horizon ones do not.

It's easy to tell for NMEA 0183 radios - just go to the wiring information in the manual and look to see if there is a DSC input.

Until there is a radio that takes DSC input, there isn't much reason to build that capability into OpenCPN.

Actually, there are many VHF radios which have NMEA 0183 input but they are mostly restricted to accepting GPS RMC etc. so that the Lat/Lon can be broadcast with Distress and Position msgs. Others, such as the Icom model mentioned in another post are now starting to take the remote command option further.

Even so, there is a question as to how many boaters can/want to communicate with the limited DSC functionality beyond Distress given the wide coverage of mobile phones for coastal private communication.

[NahanniV]

It seems that all the current ICOM radios accept dsc messages for setting up a call.

Originally Posted by stevead

I have been successfully "controlling" my Icom M504 VHF DSC radio with NMEA DSC sentences with my own software. I can successfully initiate Individual, Group, Poll & Position requests.

I have not attempted DSC Distress Alerts, Urgency or Safety messages, because of the potential consequences ! Should really try and find a training centre with interconnected radios that are not connected to antennas !

If I remember correctly I logged a request in Flyspray with outlining the NMEA DSC sentence format that operates with my Icom M504. Not sure what other brands of radios correctly adhere to the NMEA DSC sentence format.

May also attempt the same with a MF/HF radio to see if I can code the MF/HF frequencies correctly in the NMEA DSC Sentence.

[Gypsy23]

After further tests with the sentence/msg samples I have updated my table here:

File                                  OCPN        E120W        
dsc_distress_unspec                   Distress     Distress        
dsc_selfposrep                            Position      Distress    Note 1    
dsc_coastrelay_allships               Position      Distress        
dsc_coastrelay_individual            Position      Distress        
dsc_coastrelay_area                    Position      No Response        
dsc_pollposrep                            Position      Position      Note 2    
dsc_coastack                               Position      No Response        
dsc_distress                                Distress      Distress        
dsc_selfcancel - Distress active     Cancels       No Response        
dsc_selfcancel - No Distress          Position    Distress        
                
Note 1: If prior message was Distress
Note 2: No Response if prior message was Distress 
Note 3: A message with an invalid GPS number is ignored

It can be seen that OCPN honours the type of call more correctly than the E120W. The E120W seems to produce a Distress notification if it doesn't know how to interpret the message whereas OCPN produces a Position notification by default. In fact I had quite a bit of inconsistency of results with the E120W and it took time to find a pattern. The best I can say is that it will react differently to some messages depending upon what message was last displayed.

Interestingly, even though I note that msgs with an invalid GPS number are ignored, I found that if I edited a known good Position msg to change the GPS data to be invalid, updating the checksum too, the E120W would still pop-up a position notification with the last known good GPS info for that MMSI. Maybe that is a feature so that it gives Position data as close as it can. As soon as I further edit the msg to change the MMSI it is then ignored.

In summary, I feel comfortable that OCPN responds predictably and correctly for the sample messages. The RM E120W less so, but still usefully for real Distress msgs.

I would be interested to hear of results from tests with other plotters, including later model RM units. My E120W is using v2.65 firmware which I believe to be the latest and it is unlikely to be updated. Anyone know of later versions?

As some following this thread will know, this testing began when I found my GME VHF DSC msgs could not be read by OCPN because it uses $CV as a talker ID and OCPN only recognises $CD DSC talkers. This thread mentions my change request in Flyspray and Pjotr has suggested a simple change to accommodate all communication IDs beginning with C. I look forward to it being incorporated so I can use OCPN connected to my VHF.

Thanks to all the good work by the developers.
Ray

Woops! Still can't get the table right.

[PjotrC]

Originally Posted by Gypsy23

It can be seen that OCPN honours the type of call more correctly than the E120W. The E120W seems to produce a Distress notification if it doesn't know how to interpret the message whereas OCPN produces a Position notification by default.

(...)

if I edited a known good Position msg to change the GPS data to be invalid, updating the checksum too, the E120W would still pop-up a position notification with the last known good GPS info for that MMSI.

The whole of DSC protocol is very complex indeed, especially when taking into account the possibility of e.g. losing a weak ship's transmission, but receiving a strong ack for it from the shore station (or the other way around, however less likely...).

In fact I have filed a bug report, asking OCPN to ignore messages with undefined position. I think they are of no interest to the chartplotter, unless one really intends to cover all possible states of communications, which would be a very tall order. The only gain would be breaking the timeout, but I think DSC targets are so scarce, that there is no need to timeout them at all.

I would also now treat all "distress relay" messages as distress, as E120 does, but - let me point this again - without setting an alarm, even on an original Distress. The approved radio set is the device to handle the alarms, no need to initiate a second one. Plotting in red on top of all other objects, keeping at top of Target List, regardless of distance, should be sufficient support.

Also I do not know if any popular DSC sets implement anything more than DSCDSE for Distress and for Position report... NMEA allows for more, but finally it is up to the device. So maybe no one ever generates a NMEA message for an ACK.

One possible caveat with Relays is that - at least in most of what I have actually witnessed - they usually come from coast station with an unspecifiied position, being of the type "windsurfer missing in the Bay of... keep lookout and report..." announced in Voice. But again, this is then sufficiently handled by the GMDSS radio, nothing to add here from the chartplotter.

[rgleason]

Have added the last two posts to "Comments" in the Wiki.
See
DSC and Buddy via AIS. | Official OpenCPN Homepage