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Old 16-08-2017, 18:16   #1
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GPS for Use with Laptop and OpenCPN

Help this Luddite out? What is the best UBS connected GPS unit to get for a laptop that will support OpenCPN?

I see cheap ones at retailers and expensive ones and I can't really figure out the difference. Do the cheap ones just show position and not course and speed? Any insight much appreciated.
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Old 17-08-2017, 04:08   #2
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Re: GPS for Use with Laptop and OpenCPN

Hi Drew,
a GPS receiver can only determine the position. Speed and direction is calculated by the receiving application (Opencpn in your case). It does that by looking at the multiple positions received over the last seconds.
To answer your question: A cheap USB GPS receiver (they start at around 15 EUR / USD) should be sufficient as long as you can receive enough satellite signals from where you are operating it (I assume under deck). My Gps antenna works fine under deck on a steel boat next to a window.
Cheers Patrick
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Old 17-08-2017, 07:14   #3
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Re: GPS for Use with Laptop and OpenCPN

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Hi Drew,
a GPS receiver can only determine the position. Speed and direction is calculated by the receiving application (Opencpn in your case). It does that by looking at the multiple positions received over the last seconds.
To answer your question: A cheap USB GPS receiver (they start at around 15 EUR / USD) should be sufficient as long as you can receive enough satellite signals from where you are operating it (I assume under deck). My Gps antenna works fine under deck on a steel boat next to a window.
Cheers Patrick
What you say is not exactly correct. GPS receivers in fact measure course and speed and they send that data in the NMEA stream. At the bottom of the OpenCPN you see coordinates, course and speed values. These are not computed by OpenCPN. They come directly from the GPS data and can be optionally filtered to take out jitter.

The Dashboard tool shows GPS course and speed. These come from NMEA and are not computed from position. They can also be filtered to take out jitter.

The track log feature computes the average speed between points in the log. This is the only time OpenCPN computes speed from position.

The reason speed comes directly from GPS is because small distances moved result in huge error in speed computations. Therefore GPS units use a completely different method to measure speed. It does not come from two position measurements. The best GPS units do a better job of measuring speed than super cheap ones.

I would stay away from really cheap GPS units for serious navigation where safety is a concern. For experimenting they are probably fine.
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Old 17-08-2017, 07:36   #4
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Re: GPS for Use with Laptop and OpenCPN

I use a BU but we got one of the original BU units with fake chips. This is a no deal as Win tends to blind the driver (Linux meanwhile does not care). I like the BU but their attitude with the older model sucks. (Solution: plug the BU into a wifi router and use it wirelessly).

Otherwise: model 19 Garmin is a great kit and collects glonass.

Otherwise: nearly any handheld can be used with either its own usb cable or more commonly a serial/usb cable.

Otherwise: share your smartphone or tablet gps data over BT or Wifi - free and merry if you have a smartphone or tablet. But this method implies it may be simpler to navigate right on the phone or tablet and leave the laptop onboard.

Cheers,
b.
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Old 17-08-2017, 09:31   #5
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Re: GPS for Use with Laptop and OpenCPN

Thanks, folks. I get it now.
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Old 17-08-2017, 11:23   #6
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Re: GPS for Use with Laptop and OpenCPN

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Originally Posted by Drew13440 View Post
Help this Luddite out? What is the best UBS connected GPS unit to get for a laptop that will support OpenCPN?

I see cheap ones at retailers and expensive ones and I can't really figure out the difference. Do the cheap ones just show position and not course and speed? Any insight much appreciated.
Not sure how you are defining "best" so it is hard to answer your first question. There are quality differences in GPS units. The ability to pick up satellites is a function of several things and some units are better than others. Some units also process data from a greater number of satellites, and some process data more times per second; both of which should be more accurate. Some units also have a display screen and other functions.

Keep in mind that boaters are not the only folks who use these units. Maybe the best known aircraft grade GPS is the Bad Elf. I have one of those units, as well as several other less expensive ones. I do notice a difference in speed between the Bad Elf and others, but it has never been more than .2 knots. Not sure how to assess how accurate they are since I can only use one at a time on my iPad or laptop. One reason I like the Bad Elf is I could use it as a stand alone to get back home if my Garmin plotter and my iPad and my laptop all died on the same trip. It does not have things like depth, nav markers, and other things like a real plotter does, but it does have gross markings like cities.

If you can afford it I would get a Bad Elf, other wise there several good quality units which should all be under $US100.
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Old 17-08-2017, 11:27   #7
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Re: GPS for Use with Laptop and OpenCPN

Rather than buy a separate GPS at all, we all own one if we have a mobile phone.

Now, the GPS data is only a few simple "sentences". So, can anyone tell me how one can Bluetooth connect the mobile phone GPS to Windows 10 so that the sentences can be used in OpenCPN?

I am being agnostic as to mobile OS.
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Old 17-08-2017, 12:04   #8
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Re: GPS for Use with Laptop and OpenCPN

Would add to check that a cheap GPS is giving NMEA output. Windows 10 has now moved to 'location services' using a different standard to communicate with internal and external GPS's for onboard maps such as windows maps and google maps. There are now USB GPS plugings that use this standard and may not be able to provide a position for marine nav programs that look for NMEA data.
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Old 17-08-2017, 12:17   #9
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Re: GPS for Use with Laptop and OpenCPN

I've used a very cheap unit (BU 353) for years. Very reliable still under $30 at Amazon. It is a dongle with UPS cord. You download free software to start it up. I'm pretty sure it reports position and nothing else, your OpenCPN program calculates course and speed and I find it very accurate. Going for a more expensive receiver is a waste IMO.
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Old 17-08-2017, 12:22   #10
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Re: GPS for Use with Laptop and OpenCPN

I bought one of these to play with. I have not used it other than to see if it would update OpenCPN and it did. I have not used it in real world tests. It ships on a SLOW boat from China.

https://www.newegg.com/Product/Produ...0002-_-Product
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Old 17-08-2017, 12:34   #11
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Re: GPS for Use with Laptop and OpenCPN

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Originally Posted by Drew13440 View Post
Thanks, folks. I get it now.

For the record, I own both a HOLUX and the popular BU-353. Neither have what you'd call intuitive setup programs, but I am an old hand at COM ports and related nonsense and got them to work on a series of netbooks. With Open CPN, the hardware requirements are pretty low, so just stuff a basic lappie full of RAM and make sure it's got a reasonable graphic card in it. Most of the HP line would work at the $500-$700 mark. Just buy maximum RAM to make it speedier.
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Old 17-08-2017, 13:04   #12
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Re: GPS for Use with Laptop and OpenCPN

I have been using Open cpn on my laptop connected to my Garmin 72 gps for about 6 years on the west coast of south africa. This has been super reliable and very accurate for me. Course and speed always on display on the gps.
Garmin Marine Products: GPS 72H™ Marine Bundle
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Old 17-08-2017, 13:46   #13
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Re: GPS for Use with Laptop and OpenCPN

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Originally Posted by Dave22q View Post
I've used a very cheap unit (BU 353) for years. Very reliable still under $30 at Amazon. It is a dongle with UPS cord. You download free software to start it up. I'm pretty sure it reports position and nothing else, your OpenCPN program calculates course and speed and I find it very accurate. Going for a more expensive receiver is a waste IMO.
Thats what I have
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Old 17-08-2017, 14:06   #14
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Re: GPS for Use with Laptop and OpenCPN

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I'm pretty sure it reports position and nothing else, your OpenCPN program calculates course and speed and I find it very accurate.
Did you read where UYA said the same thing and transmitterdan corrected him? transmitterdan is correct; the COG and SOG comes from the GPS dongle. I don't mean to be rude, but once false info has been corrected one should be reluctant to repeat the error and spread the ignorance.

Next time you are in OCPN go to the configuration of the GPS connection and turn on the monitor. Then look at the stream of NMEA 0183 data that is coming from the GPS and you will find the sentences that include SOG and COG.

The Garmin units in the past have used a proprietary format for their data IIRC. Many of the available GPS dongles do have a proprietary format available but default to NMEA 0183. I am unfamiliar with the Windows format - perhaps M$ is trying to streamline the data flow in a similar way to the GPS vendor's formats. All this stuff keeps the GPSd folks busy.

There are significant differences in the GPS dongles. The really old ones wouldn't receive well if down below or inside of a house. Newer ones have much better receivers. The volume market for GPS modules is now for mobile phones, which requires low cost and low power consumption - no surprise that they are not quite as sensitive/fast as other modules. Also, the phone GPS units usually support downloading the ephemeris from the internet in order to speed up time to first fix. The dongles that use these chips are not as good for our purposes.

The original BU-353 GPS dongle used a SirfStar III module, which is very good. The current BU-353-S4 uses the SirfStar IV, which is not considered to be as good (presumably a phone unit). The guys that are into this stuff like the uBlox 6 and 7 modules, although that may have moved on. I am not absolutely current. I will check with my brother, a GPSd developer, to see which modules are currently at the top. (Don't hold your breath - he is currently flying into Madras for the eclipse.)

Another thing to consider is if the module supports the Russian (GLONASS), Chinese (BAIDU), and European (Galileo) alternatives to the GPS system.

If you want to share the GPS info with several programs then install GPSd, the GPS daemon.

Greg
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Old 17-08-2017, 14:17   #15
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Re: GPS for Use with Laptop and OpenCPN

If your brother is a GPS developer perhaps he can answer the question that I posed:

=> How can one get the GPS signal out of a mobile phone connected via Bluetooth?

Whilst I am at it, it also infuriates me that my Garmin chart plotter will replicate itself via WiFi or BT on an iOS device or an Android one but there is no app for Windows to so the same. My Microsoft Surface is a far superior device to my iPad and I would much prefer to use it on the chart table.
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