GPS+GLONASS, how much improvement?

[nhfours]

I am currently hiking in Switzerland, and often hike in valleys with moderately steep walls. My GPSr (GPSMap 60 CSX) often loses the signal, and looking at the satellite page shows many satellites rather low on the horizon. That led me to wonder how much GPS+GLONASS would help.

 

A bit of Googling told me that the new Etrex GPSr line has (or will have) GPS+GLONASS. I would love to hear from the GNSS experts how much performance improvement this combination will have.

 

Thanks!!

[+ecanderson]

I am currently hiking in Switzerland, and often hike in valleys with moderately steep walls. My GPSr (GPSMap 60 CSX) often loses the signal, and looking at the satellite page shows many satellites rather low on the horizon. That led me to wonder how much GPS+GLONASS would help.

 

A bit of Googling told me that the new Etrex GPSr line has (or will have) GPS+GLONASS. I would love to hear from the GNSS experts how much performance improvement this combination will have.

 

Thanks!!

If you're in deep valleys, you will see the same sorts of problems with GLONASS as you do with any GPS system (current or future) ... if you can't get a clear view to more than one or two satellites, you aren't going to get a lock. If you can't get a clear view to at least a good handful of satellites, you're going to have lousy EPE readings. While it's possible that the addition of one or more GLONASS satellites to the constellation your unit can 'see' might make a difference, that kind of terrain just doesn't lend itself to GPS satellite reception. And unless these newer eTrex units are capable of concurrent (not configured) reception of GLONASS alongside the existing constellation, it won't matter at all. I haven't seen how they're managing this yet.

[+GPSlug]

Combined GPS+GLONASS will give you some more availability in situations where using GPS on it's own is impossible or has really bad geometry. That's really the only benefit.

 

Generally, if GPS on it's own is working adequately but not great, adding GLONASS won't improve accuracy. It isn't quite like there being 24 more GPS satellites in orbit. GLONASS isn't as accurate as GPS, so seeing additional satellites from GLONASS won't help as much as if they were GPS satellites. You also won't get EGNOS corrections for GLONASS.

 

In your valleys you might get a position more often, but it still won't be great. If your problem is more about getting the ephemeris for new satellites (i.e. your satellite page has bars but they won't go solid) because of both the valley walls and big trees, you might get more improvement from an external antenna.

[+splashy]

You can see sats. but when they show all more or less after each other, its near to nothing, the gps needs a broader sat view.

Try wearing the gps on or near to you shoulder, wearing it on a belt shields a sat view almost completely ( left and righ steep walls, you and maybe one or more persons right in front of you.

How broad is the canyon or valley you're talking about, do you have very heavy clouds?

[RamblinBear]

As a professional GPS user, I use an Ashtech MobileMapper 100 which is capable of using both GPS and GLONASS signals (as well as SBAS corrections - EGNOS here in Europe). It routinely picks up at least 12 to 14 satellites in the field, which enables position fixes which are both faster and more reliable. There is also a slight accuracy improvement due to the greater number of sats in view and the generally better geometry of the sats.

 

Granted, the Ashtech is a professional grade unit, capable of sub-metre accuracy (should be, it cost £3500), and there will be compromises in the production of consumer grade handsets, but so long as the capability to receive GLONASS is implemented properly (so that the handset can receive upto perhaps 20 satellites at a time, rather than still being pegged at 12 satellites), then I think recreational users will still see substantial benefits with GPS+GLONASS handsets. I'm awaiting reviews and digests of the new Etrexes with considerable interest, and wondering whether there will be revised Montanas and GPSMap62s waiting in the wings shortly which will also be GLONASS ready.

[+coggins]

That's really the only benefit.

 

You are missing the cost factor. Russia is planning on imposing an import duty (25%) on GPS receivers that do not have GLONASS. So by adding GLONASS reception, importers will not be hit with the added cost, resulting in a lower end sales cost.

 

Threat of import duties to increase appeal of GLONASS

[RamblinBear]

Interesting. Adds a new slant to Garmin's (and others') motivations for adding GLONASS. Works out well for users though.

[RamblinBear]

Also a stark contrast between the Russian Federation seeking to protect their investment in GLONASS versus the FCC in the US and the LightSquared debacle.