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Old 18-11-2016, 09:06   #1
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Tracking and plotting multiple GPS devices

I was wondering if OpenCPN has the ability to track and plot multiple GPS devices simultaneous. One for out ship and another for some towed equipment. I see that I can make and enable multiple data connections but it seems to only track and plot one. Thoughts?

Thanks,
Brian
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Old 18-11-2016, 12:06   #2
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Re: Tracking and plotting multiple GPS devices

You can use a "portable" install of opencpn in parallel with your main installation, and connect the "towed" gps to the portable installation - it should work fine.

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Originally Posted by BrianCarrollr View Post
I was wondering if OpenCPN has the ability to track and plot multiple GPS devices simultaneous. One for out ship and another for some towed equipment. I see that I can make and enable multiple data connections but it seems to only track and plot one. Thoughts?

Thanks,
Brian
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Old 19-11-2016, 00:19   #3
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Re: Tracking and plotting multiple GPS devices

It would be nice if the nmea0183 input signal for a second gps device could be converted to a unique symbol and plotted, without intterfering with the primary gps. I wonder if the plugin NmeaConverter would be any help in this regard?
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Old 21-11-2016, 04:51   #4
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Re: Tracking and plotting multiple GPS devices

I'll give it a try, thanks.
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Old 21-11-2016, 05:20   #5
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Re: Tracking and plotting multiple GPS devices

Greetings and welcome aboard the CF, Brian.
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Old 21-11-2016, 05:20   #6
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Re: Tracking and plotting multiple GPS devices

NMEA0183 does not implement different source instances for one data type or sentence (but the talker ID, which is normally neglected).
Different from N2K or SigK.

When having several GPS on a N2K backbone, converting the messages into a NMEA0183 message will result in a mess. One can only filter out or giving priority on base of the known source (in this case)

So GPS is GPS - you don't know about the source of a RMC or GLL message.
Data from from more than one sounders is another example.

If the signals of the different GPS do enter from different ports one might convert the GPS related message into a MARPA target for example (with some not that difficult programing). Being always a proprietary solution.
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Old 21-11-2016, 05:47   #7
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Re: Tracking and plotting multiple GPS devices

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Originally Posted by bcn View Post
NMEA0183 does not implement different source instances for one data type or sentence (but the talker ID, which is normally neglected).
Different from N2K or SigK.

When having several GPS on a N2K backbone, converting the messages into a NMEA0183 message will result in a mess. One can only filter out or giving priority on base of the known source (in this case)

So GPS is GPS - you don't know about the source of a RMC or GLL message.
Data from from more than one sounders is another example.

If the signals of the different GPS do enter from different ports one might convert the GPS related message into a MARPA target for example (with some not that difficult programing). Being always a proprietary solution.
Thanks for this information. Is there any suggestions of a software to handle what I'm looking for you can think of? I guess based on what you've said, this may be a limitation all around yes?
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Old 21-11-2016, 06:09   #8
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Re: Tracking and plotting multiple GPS devices

The easiest solution probably is to convert your "second" GPS data into APRS (which "abuses" the WPL NMEA sentence to report position) before feeding it into OpenCPN. It will be pretty simple to implement. Or AIS, which will give you the luxury of being able to send COG/SOG etc., but the encoding is more complicated.

I am unfortunately not aware of any completely ready solution for your use case (other than placing an AIS transponder on the towed object).

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Old 21-11-2016, 06:28   #9
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Re: Tracking and plotting multiple GPS devices

Thank-you, I'll look into this.
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Old 21-11-2016, 07:23   #10
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Re: Tracking and plotting multiple GPS devices

Quote:
Originally Posted by petter5 View Post
You can use a "portable" install of opencpn in parallel with your main installation, and connect the "towed" gps to the portable installation - it should work fine.
This may be the way we go thanks.
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Old 21-11-2016, 08:14   #11
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Re: Tracking and plotting multiple GPS devices

Brian,

perhaps this is something for you:
http://www.gdayii.ca/Downloads/AISTTM.zip
(from phiggins)

Hubert
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Old 21-11-2016, 09:42   #12
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Re: Tracking and plotting multiple GPS devices

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Originally Posted by petter5 View Post
You can use a "portable" install of opencpn in parallel with your main installation, and connect the "towed" gps to the portable installation - it should work fine.
How are you going to connect the GPS on the towed object to OpenCPN? If the towed object is so close that you can run a USB cable between the vessels why do you need two GPS positions?

It seems to me this is an ideal application for a personal locator AIS beacon. You put it on the towed vessel, follow it on your OpenCPN on your boat, and you have everything you need. Plus, if you lose the tow line you can easily find the towed vessel and reattach. Trying to do this with a second GPS (with or without a second OpenCPN instance) seems like a really hard way to solve a simple problem.

Fabbian
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Old 21-11-2016, 09:49   #13
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Re: Tracking and plotting multiple GPS devices

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How are you going to connect the GPS on the towed object to OpenCPN? If the towed object is so close that you can run a USB cable between the vessels why do you need two GPS positions?

It seems to me this is an ideal application for a personal locator AIS beacon. You put it on the towed vessel, follow it on your OpenCPN on your boat, and you have everything you need. Plus, if you lose the tow line you can easily find the towed vessel and reattach. Trying to do this with a second GPS (with or without a second OpenCPN instance) seems like a really hard way to solve a simple problem.

Fabbian
The towed system is an underwater towed body that will have a fibre optic cable connection outputting NMEA data for position. There are plans down the line for our own position display but for sea trials we are exploring some simple display options.
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Old 21-11-2016, 10:26   #14
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Re: Tracking and plotting multiple GPS devices

Quote:
Originally Posted by BrianCarrollr View Post
The towed system is an underwater towed body that will have a fibre optic cable connection outputting NMEA data for position. There are plans down the line for our own position display but for sea trials we are exploring some simple display options.
In this case a programer should not have too much work to send either a AIS position message or a TTM message. Or Pavel's proposal, APRS.
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Old 21-11-2016, 11:18   #15
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Re: Tracking and plotting multiple GPS devices

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The towed system is an underwater towed body that will have a fibre optic cable connection outputting NMEA data for position. There are plans down the line for our own position display but for sea trials we are exploring some simple display options.
Well GPS won't work underwater so that is a problem.

If you are going to attach a surface buoy then that could have GPS position, using wifi or some other form of data link. A class B AIS beacon will likely update too slowly.

Sounds like your doing some kind of surveying. The simpler systems that I have worked on use a highly accurate GPS on the vessel and then the length of tether and depth sensors if fitted, or estimated, and some simple trig to calculate the position of the fish.

If you let us know what it is that you are working on we may be able to offer more specific help.
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