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Old 03-04-2015, 12:26   #1
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What is the advantage of GPS and Glonass?

What do I have for advantage of a navigator that receives signal from both GPS and Glonass?
I will have more satellites to determine my position, but do that mean that I will have a more accurate position?
With more satellites I will probably get a fix faster when I start the navigator, but my navigator is always on so that will not be any big advantage.
Garmin GLO takes signals from both GPS and Glonass and have a update frequency of 10 Hz, but that’s not because it takes both signals, other pure GPS receivers do also have that feature.
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Old 03-04-2015, 12:44   #2
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Re: What is the advantage of GPS and Glonass?

Source Wiki :
satellites are located in middle circular orbit at 19,100 km altitude with a 64.8 degree inclination and a period of 11 hours and 15 minutes.


Due to this inclination, Glonass provides a better service than GPS over sub arctic regions...
Else, just like you I was also wondering about Glonass benefits, without hijacking your thread, I searched the web to find out if "pure" Glonass Satnav existed, but I could not find any.
Would be interesting to review side by side a GPS vs a Glonass Satnav.
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Old 03-04-2015, 13:06   #3
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Re: What is the advantage of GPS and Glonass?

We have some good experts on GNSS systems and I'd like to hear what they have to say on this.

My main receiver gets GPS and GLONASS, but I notice that the GLONASS satellites, although they show up as being received, are not apparently being used for navigation. I don't know why.
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Old 03-04-2015, 13:09   #4
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Re: What is the advantage of GPS and Glonass?

https://en.wikipedia.org/wiki/GLONASS

Wiki says comparable accuracy but if you've got twice as many satellites to use, and the receiver was smart enough to use them, it might be able to get better accuracy more often more quickly that way. Might.

I had heard the new system the EU is putting online will actually have better accuracy then either, but if five or ten meters isn't accurate enough for your navigation, I would suggest a stout cord attached to the dock might be better than a GPS system.(G)

Glonass will, of course, only be of use if Vlad Putin doesn't decide the turn it off while he's "liberating" your boat.
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Old 03-04-2015, 13:42   #5
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Re: What is the advantage of GPS and Glonass?

So we are three (Edit 4) so far.
;-)
Glonass/GPS in smartphones :
What is GLONASS in Mobile Phones | thetecnica


I am dubious about some explanations, tough.


@ Hellosailor, Vlad is welcome to "liberate" my boat from Somali pirates, in the somehow "straight forward" Russian way anytime, Vodka is on me.
:-)
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Old 04-04-2015, 07:18   #6
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Re: What is the advantage of GPS and Glonass?

The accuracy of any position fix depends on the orientation of the lines of position. In GNSS navigation, the orientation of the lines of position from satellites depends on the particular moment in time, the orbits of the satellites, and your position. In GNSS navigation, the metric Dilution of Precision (DOP) expresses the quality of the lines of position and their orientation to each other. The lower the DOP, the better.

By being able to use satellites from both constellations, GPS and GLONASS, the chances of having satellites in positions which produce a lower DOP is increased. On that basis, being able to use both GPS and GLONASS may lead to more accurate position fixes.

As noted already, the orbits of satellites in the GLONASS constellation are inclined to a higher angle, producing better coverage at higher latitudes. This advantage is probably most significant in polar regions. Whether or not you'll be doing much boating in polar regions is hard to say; that advantage of GLONASS may not be obtained by many boaters.

In general, GNSS receivers for use aboard recreational boats are not particularly close to the state of the art. Determining a position of a boat with an accuracy of a few meters is quite acceptable. GNSS technology exists now which can deliver much better accuracy than that, but there is seldom any need or justification to have that much precision when navigating a recreational boat.

In addition to GPS and GLONASS, there are several other GNSS systems in operation:

--BEIDOU (or COMPASS) from China

--IRNSS from India

--GALILEO from a European consortium

--QZSS from Japan

In addition to improved accuracy from improved DOP, some of the above GNSS's have fundamentally better accuracy provided for in their signals. Whether or not any advantage can be obtained in practical application probably awaits being determined.
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Old 04-04-2015, 11:58   #7
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Re: What is the advantage of GPS and Glonass?

Having just bought a new mobile phone I was impressed by the speed of fix now it can access the GLONASS constellation as well as the GPS one. Almost instant fix on 15 satellites and an error of 5m.

So based on this I'd say the main advantages will be:
Faster fix,
Better accuracy,
Less "loss of signal"

With GLONASS also giving better coverage of Arctic and Antarctic regions than GPS this will also aid those sailing in those areas.

Once Galilleo is fully operational we should see even better signals, better response time and perhaps accuracy down to the cm level assuming of course that our chartplotters are able to access the signals and process them.

And it is not just Mr Putin that can switch off sat nav signals. Mr Obama can do the same thing if he feels like. Being able to access multiple systems should mean we are never left totally in the dark, well hopefully.
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Old 04-04-2015, 12:05   #8
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Re: What is the advantage of GPS and Glonass?

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Originally Posted by kas_1611 View Post
Having just bought a new mobile phone I was impressed by the speed of fix now it can access the GLONASS constellation ...
I doubt that the speed of initial position fix is due to GLONASS.

Mobile devices with a GNSS receiver now make use of Assisted GPS. They receive the navigation message from the high-speed data network of their cellular carrier, instead of spending 15-minutes getting if from the 50-bps transmission on the GPS signal.

A modern GNSS receiver with AGPS that is connected to a modern cellular network can have a time to first fix of less than a second. This feature is exploited to save power. The GNSS receiver segment of the device can be shut off to save power and then turned on, and a fix obtained, in a second, when a position fix is needed.
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Old 04-04-2015, 12:13   #9
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Re: What is the advantage of GPS and Glonass?

Don't count on AGPS over cell phones, it relies on a whole chain of dependencies, like your carrier, whether you have signal (you won't offshore), and the entire internet.

When Samsung brought out their first "Galaxy" smartphone, the Samsung Captivate, in the US, people complained about slow GPS lock times, or no lock time. Samsung blamed it on the carriers, who blamed it on Samsung.

But if you turned on the right service menu on the phone, it showed the AGPS software was pointed at a specific AGPS server, which Samsung had SHUT DOWN before the phones were released. So, no server? No AGPS.

Eventually Samsung said this problem (which they never acknowledged) was fixed by an OTA release. Which the service menu showed could not fix it, since it still pointed to the same ghost server.

After SIX MONTHS of this, the solution was still for users to manually open the service menu and manually enter the web address of a Google AGPS server, intended for Google Maps (etc) users, which kindly worked.

The prudent mariner should never really rely on anyone in the cell phone business for anything. Except incorrect bills.
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Old 04-04-2015, 12:26   #10
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Re: What is the advantage of GPS and Glonass?

Well as my SIM card had yet to be activated by my carrier due to a change over from monster to nano sim there was no mobile signal to get any AGPS data from and I still got a fix in only a few seconds off more satellites than I ever saw on my old mobile (like 4 years old) so I can only put it down to the extra data from the Glonass constellation.

I also get a very fast fix when the phone is in Airplane mode or without Wifi connection.

Perhaps my Sony Xperia has a little imp inside with a map and compass as well as the GNSS receiver to give such a fast fix

Like any prudent navigator I never rely on a single system
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Old 04-04-2015, 17:31   #11
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Re: What is the advantage of GPS and Glonass?

I dont think you have to worry about Mr. putin or Mr. obama turning off any navigational system their military forces rely on them for navigation. Now Mr putin turning off Mr. obama's or the converse might be a possiblity. Remember Mr Putin's system was the original Global Positioning system, though they were close going on line.
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Old 04-04-2015, 18:19   #12
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Re: What is the advantage of GPS and Glonass?

In open waters, one can see all the way to the horizon in ALL directions ... there are more than enough satellites to choose from ... no matter what system.
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Old 04-04-2015, 19:04   #13
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Re: What is the advantage of GPS and Glonass?

You have two constellations, two positioning systems. If one goes pop, you still have the other one. This is caused redundancy. Redundancy is good.

You have two position fixes. If they agree, you may be where you think you are. If they disagree, you start thinking. Thinking is good.

You can use two signals combined to arrive at one, more accurate fix. (A claim from manufacturers and testers).

Having two sat systems does not free you from the possibility of using other methods of finding your fix (like e.g. piloting, when inshore). But since you asked for advantages, I have not said this one.

We have GLONASS on the phone but I am buyiing a proper GLONASS and/or GPS receiver next, if only to have some techno fun on our next trip.

Cheers,
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Old 04-04-2015, 22:01   #14
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Re: What is the advantage of GPS and Glonass?

Learn to celestial navigate. Only God can turn off the stars. For everything spent on the obsession for persuasion, someone else is deprived. One World, One People, Think about it.
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Old 05-04-2015, 00:39   #15
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Re: What is the advantage of GPS and Glonass?

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Learn to celestial navigate. Only God can turn off the stars. For everything spent on the obsession for persuasion, someone else is deprived. One World, One People, Think about it.
He doesn't have to turn the stars off, he simply has to hide them for a few days. This happens regularly although I'm not sure who is responsible when this happens .

Usally not a problem offshore but can be serious if closing a coast under a heavy overcast and one has being on DR on past week
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