Picking up data from OpenCPN

[Antipole]

My existing Mac set up has my ship's log written in FileMaker which collects data (position and other data such as HDG, CMG, wind, depth etc.) from MacENC via AppleScript calls. So when I log start/end of passage or any event, these data get added to the log automatically.

Given Catalina no longer supports 32bit apps, I am moving to OpenCPN instead of MacENC and from FileMaker (64bit too expensive) to, likely, TapForms for the log. (BTW TapForms supports JavaScript coding.). I have OpenCPN receiving my NMEA data fine.

So, I need a way to programmatically collect the above data from OpenCPN. Unfortunately, OpenCPN has no AppleScript support. The Dashboard plugin has the data but I see no way of extracting it - not even by copy & paste.

Any suggestions as to how I can get at this data will be much appreciated. I am not up to speed on plugins, so would need pointers if I have to go down that route. Thanks.

[CarCode]

You may use VDR. It is a plugin available for Mac also:
https://www.opencpn.org/OpenCPN/plugins/vdr.html

[Antipole]

@carcode - thanks for pointing me to VDR. I have installed it and played the sample file.

As I understand it, VDR allows me to record the NMEA data stream but I would need to post process that to extract the data I want retrospectively. There is no way of getting it to pass out the data on demand?

[CarCode]

Perhaps you want to try the Logbook Konni? It has some features you are looking for:
https://www.opencpn.org/OpenCPN/plug...bookkonni.html

[transmitterdan]

Originally Posted by Antipole

@carcode - thanks for pointing me to VDR. I have installed it and played the sample file.



As I understand it, VDR allows me to record the NMEA data stream but I would need to post process that to extract the data I want retrospectively. There is no way of getting it to pass out the data on demand?

OpenCPN has the ability to connect to a simple TCP socket and send all NMEA data in close to real time to that socket. You could create a Python or Java script to act as a TCP service which OpenCPN will happily deliver all the NMEA data. At that point you have to parse the NMEA protocol but that is not too difficult and I think a search may turn up existing code to do that. Depending on exactly what data you are interested in parsing may be trivially easy.

[teppokurki]

Consider installing Signal K server and routing data from O to SK via TCP. SK will parse NMEA0183 and provide a simple HTTP api to access the latest values on demand. You can use curl from AppleScript to do http if that is your tech of choice.

https://github.com/SignalK/signalk-server-node/

https://stackoverflow.com/questions/...plescript-rest

[CarCode]

Why not a little bit more complicated?
It is winter time, people cannot sail and have so much time...

[teppokurki]

Yep. Complicated/simple is in the eye of the OP...

Given Tap Forms has js that would be my choice for http data access.

[Antipole]

Thanks for the suggestions.

Looks like simplest would be to write Javascript within TapForms to read the NMEA stream directly, without going via OpenCPN. There are recipies for this - it does not look fearsome. I have set up my NMEA2000-WiFi gateway to send NMEA0183 data over UDP, so this should keep things simple - no open and closing of connections.

It will take a while before I can get around to this but I will report back in due course.

[rgleason]

Carcode suggested Logbook konni, and if it has all the data you want, it might be very easy to use. The data set has been extended several times.

However the signalk and vdrplayer suggestuons are also good.

[Antipole]

Turns out JS cannot access network data (TCP or UDP) - at least I have not found any way.

Given that any web page visited can download any JS and execute it, JS is very restricted as to what it can access outside its own walled garden. Otherwise a web page could read any network traffic on your computer or any file etc. So these restrictions are understandable, especially on Apple devices.

[teppokurki]

These restrictions are runtime environment specific: browser sandbox is very different from Node.js, where UDP and TCP work. I guess TapForms’ js support has browser ancestry.

Your problem underlines the reasons Signal K exists: to provide an easy way to access marine data, without the need to fiddle with lower level protocols (http/ws versus tcp) and nmea parsing (json versus NMEA0183/2000).

[Antipole]

I have a solution - not actually via OpenCPN, but for neatness to close off this thread I will relate it:

I have discovered the Monkeybread plugin for FileMaker, which adds a vast array of functions to standard FileMaker, including handling both TCP and UDP sockets. I can read the NMEA data stream directly without going via OPenCPN.

This still leaves me with the issue that my Filemaker v10 is 32 bit and will not run on Catalina. Maybe I have to upgrade (£££) but that is outside the scope of this forum.