WAAS / EGNOS

[FlyingDutchman]

I am planning to buy the Garmin GPS 72.
I read, that this instrument is WAAS enabled to give it a better accuracy.
I also read, that in Europe the better accuray is achieved with EGNOS.
Will the Garmin 72 also use this EGNOS system?
Maybe a stupid question, but I know nothing about these type of things!
Jan

 

[pvb]

Yes...

WAAS and EGNOS use the same method of enhancing accuracy, so a Garmin 72 will pick up EGNOS signals. Not sure whether EGNOS actually works yet, though.

 

[webcraft]

Warning - excessive GPS accuracy may induce a false sense of security!

Any GPS will be accurate to within 100m, which ought to be good enough for anyone unless you need (eg) to position an oil rig over a wellhead to within a few inches.

If you are using GPS to navigate blind closer than this to charted dangers or seamarks then you may

a) hit the waypoint if it is a solid object (eg buoy)
b) hit other people aiming for the same waypoint
c) hit something else due to inaccurate charts


- Nick

 

[Robin]

Re: Warning - excessive GPS accuracy may induce a false sense of security!

So it would be better still to use Loran and only 1000m accuracy? /forums/images/graemlins/confused.gif

I fail to see how having greater accuracy (and especially repeatability) makes you more likely to:-


[ QUOTE ]
a) Hit the waypoint if it is a solid object (eg buoy)

[/ QUOTE ]

This assumes you put wpts on solid objects and navigate blindfold.

[ QUOTE ]
b) hit other people aiming for the same waypoint

[/ QUOTE ]

This assumes that everyone navigates blindfold.

[ QUOTE ]
c) hit something else due to inaccurate charts

[/ QUOTE ]

This assumes that you navigate blindfold.

I have a ruler calibrated in mm, should I only use it to measure metres? /forums/images/graemlins/shocked.gif

 

[Robin]

In simple tems as I understand it, EGNOS is currently working but only in test mode, it may be intermittent or even less accurate than the normal non-EGNOS position during this period. Tome is the forum man in the know if he is about. Certainly our Navman will currently run in EGNOS mode but it goes in/out of EGNOS and beeps it's warning too often to use it even if I trusted the position was not subject to test errors.

 

[john_morris_uk]

Re: Warning - excessive GPS accuracy may induce a false sense of security!

EGNOS works some of the time - parhaps most of the time in Europe - I haven't noticed the proportions.

Our GPS uses the system and when it is locked onto an EGNOS satellite you get an extra decimal place of readout and a little 'd' in the corner to tell you its working. I had to tell it to use the EGNOS system in the setup menu, and I know it drops out sometimes - just haven't noticed how often....

 

[pvb]

You mean like this?

 

[MIKE_MCKIE]

Re: You mean like this?

Don't you just love the boats name?

 

[Robin]

Re: Warning - excessive GPS accuracy may induce a false sense of security!

I only noticed it drops in/out because on our Navman each in or out is accompanied by an irritating beep and a brief screen message! Tome I think posted a review of the status last month, so a search might help, I think it was there that I saw that it could actually degrade rather than improve the fix during this test period.

 

[webcraft]

Re: Warning - excessive GPS accuracy may induce a false sense of security!

Robin, you are being pedantic . . .

I didn't say it was undesirable to have super-accurate GPS or that it was better to use a less accurate system.

What I did say was that in the world of real navigation and passage planning it is largely irrelevant and can encourage blind navigation in tight situations where, WITHOUT that assumed degree of accuracy, the passage would never have been attempted in the first place.

And I think you knew perfectly well that that is what I meant!

- Nick

 

[FlyingDutchman]

Re: Warning - excessive GPS accuracy may induce a false sense of security!

Thank you all for so much wisdom!
I normally navigate by looking around and using a map, which works fine in the area we use our boat in the Netherlands (channels, lakes).
I want to have a GPS in case the wheather turns bad (fog) or if I loose my way in unknown waters. Also, I like the features of a compass and a log.
In a way, I agree with Nick. Especially if everyone uses the waypoint books that are available in the Netherlands and everybody uses the same waypoints, an extermely accurate GPS is a potential danger. Is not this what is happening when two aircrafts collide somewhere in the air?
Thanks again,
Jan

 

[Robin]

Pedantic yes and only part serious but....

Nick

There is the qusetion of repeatabilty. Decca was less accurate than GPS but it WAS repeatable, ie if it said you were half a mile west of the actual position today it would say the same tomorrow. This meant that once you had visited a waypoint and adjusted it's Lat/Long to match what the Decca gave rather than the chart said, you could have a high degree of confidence in returning to that waypoint again next time. That repeatabilty is not inherent in standard GPS (though better with SA off as it is} but it can be by using either land based dGPS (differential GPS) signals or satellite based dGPS signals (WAAS/EGNOS) to compare and correct the position given. So you can use an inaccurate chart to navigate to closer tolerances if used with CARE and with the knowledge to do it the way described, ie don't take the chart as gospel unless previously the planned route/wpts checked out in good conditions.

The other factor with dGPS is that with more accurate positions, the changes in postion are also more accurate, so enabling more accurate SOG and COG figures, accurate enough (out of any tidal flow) to be used for calibrating log and even swinging the compass. So dGPS isn't really only useful for pinpointing an oil well head!

Robin
Pedant Extordinaire /forums/images/graemlins/laugh.gif

 

[BrendanS]

Re: Warning - excessive GPS accuracy may induce a false sense of security!

Any recent GPS will be accurate to within 15/20m at worst, probably within 3 to 8 most of the time, and even better on a good day. With Wass or Egnos, down to 0.5 to 3m

 

[MarkJohnson12345]

Re: Warning - excessive GPS accuracy may induce a false sense of security!

I think the WAAS quoted accuraccy is 7 metres at worst, and up to 3 metres at best.

.5m sounds like a differential system.

All a bit irrelevant when sailing.

I use a differential system which is accurate to better than 1". But there again it cost £30,000 or so. and I don't use it to sail with!

 

[Sammy]

I think the question was did the GPS he was buying work with egnos and/or waas I think the answer may be that the garmin may only work with WAAS which isn't very good around the UK because it only works in the US. My Garmin 276c only works with WAAS. /forums/images/graemlins/frown.gif

 

[henkm]

Sammy,

You are right about 'the original question'.
My answer to it is different from yours:
The Garmin GPS 72 will work with Egnos, AND if I am not mistaking: so will the Garmin GPSMAP 276C !

Unless you already checked Garmin themselves on this (in which case I would very much like to hear about that) I think you might be mistaking: WAAS differs a bit from EGNOS but all Garmins that I'm familiar with will understand both.

Egnos is in a test phase. On a 1,5 hour trip yesterday (North of Holland) it worked half of the time on my GPS 76. Accuracy results: not convincing, YET (will be better after test phase). GPS needs 'open sky' so no trees, buildings, etc.

Do you have 'WAAS ON' on your GPS (menu -> menu -> Waas on)?
You might also take a look at the latest firmware update for the GPSMAP 276C
(14 december 2004):
http://www.garmin.com/support/collection.jsp?product=010-00331-00

Henk.

 

[henkm]

Egnos will work on the GPS 72.

Because you are Dutch I can recommend the excellent program WaypointsGPS:
http://www.waypointsgps.nl (I have no shares in it).

Free software and more tips about GPS and PC are mentioned on my own pages (see below).

Henk

--
http://www.filo.nl/zeilen/

 

[BrendanS]

Waas only works efficiently in the US if you are European based.

Egnos is not live, though it will sporadically give signals to some GPS sets, but it is not live, and not accurate, and so you you should turn off Waas if you have that setting on your GPS.

If you are not sure about Egnos and what it's current capabilities are, do a search on the forums, there is a lot of information available

Egnos will work with a 276c

 

[FlyingDutchman]

Thanks everybody for your input!
Cheers,
Jan

 

[Anonymous]

Re: Warning - excessive GPS accuracy may induce a false sense of security!

Jan,[ QUOTE ]
Also, I like the features of a compass and a log.

[/ QUOTE ]Your post suggests that you have not used GPS before in which case I would point out the the 'compass' facility of a GPS is totally different to a conventional magnetic compass in that it does not show heading, it shows track. So, suppose you were heading 090 with a strong southerly tide, your magnetic compass would read 090 but your GPS 'compass' might read, say, 120 because that's the actual track made good (COG). Similarly, the speed is speed over ground (SOG), not through the water.

David