No Altitude on TTN2 ?

[Claude]

Dear all,

i'm new to GPS in general, so apologies if this is an obvious question:

I purchased the TTN2 Bluetooth package this week and was a little disappointed in not finding an altitude indicator anywhere within the software.

I thought the 3D indicator in the GPS Status window indicates that TomTom can receive altitude as well as co-ordinates. Am I wrong?

Finally, is there any utility/add on out there which indicates altitude?

many thanks!

Claude

[lbendlin]

Claude,

yes, the 3D fix indicates that an altitude has been calculated as well, but most of all it means you are locked onto at least 4 satellites.

TomTom is a street navigation program, and those are generally indifferent to the altitude because it is not included in any calculations.

You can use any topographical software or VisualGPS or whateve other diagnostics tool is out there - they will all show altitude.

Be aware though that some receivers are calculating the geoid correction wrong, resulting in some 40 m difference from the real value. This adds to the generally higher altitude DOP (Dilution of Precision) due to the fact that our dear earth is anything but a nice round bowling ball. It's rather pear shaped, and the WGS84 geoid that is used is just an approximation.
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Lutz

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[SimonCatlin]

[DavidW]

SBAS systems like WAAS are being rolled out in various parts of the world - the European one is called EGNOS. EGNOS should hopefully be fully operational later this year - the specification from ESA gives the quality of a fix with EGNOS as 2m accuracy horizontal, 5m accuracy vertical - both at 95% confidence.

So far as altitude figures go, particularly the perils of WGS84 ellipsoid to geiod corrections in the NMEA GGA sentence, see this thread, which, although it's specifically about the Haicom HI-303MMF, almost certainly applies to all GPSes using SiRF chipsets, which are the majority of GPSes we use with our Pocket PCs.


Meanwhile, as Lutz says, TomTom GPS doesn't display altitude figures; it has them, but as it doesn't make any use of them it doesn't display them.



David

[SimonCatlin]

David,

Your knowledge is excellent. Lets also add the Russian equivalent of GPS, which has low life satelittles and the new European Version (which will cost us all money to receive) in 2007 (ish) and I think we have the lot.

With these, GPS approaches into airports will become a reality, which will allow more aircraft flying into smaller airports. Which is good news as aviation will be the only way forward as our roads clog up!
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iPhone5, TomTom, Google maps, Navfree, Viewranger and Apple Maps (ekk)

[DavidW]

Getting off topic now - but GPS precision approaches should be possible with EGNOS in operational condition. This may be reached some time later this year - at the moment, what EGNOS signals there are contain a message that marks it out as a test signal, but it's hoped to have EGNOS fully operational later this year.

EGNOS has two tasks in the aviation setting. One is to provide a measure of whether GPS is reliable or not - though it's rare, there are times when GPS doesn't provide an accurate position fix, such as the 1 January 2004 anomaly of PRN23/SVN23 about which there's a detailed description here. EGNOS provides an integrity signal - obviously something that's very important in the aviation context.

The second task is the wide area differential correction, that improves the accuracy of the GPS signal.


There are various improvements coming in satellite positioning over the next decade. The US Government has committed themselves to introducing two new civilian GPS signals, referred to as L2 Civil and L5 Civil, in addition to the L1 C/A signal we are currently using (there's also various upgrades going on in the military side of GPS, which is encrypted and largely useless to our civilian receivers, though there are some specialist surveying receivers that use correlation techniques to improve their accuracy using the military signals; these don't require the secret encryption keys for the Precise Positioning Service). The new L2 Civil and L5 Civil signals will allow suitable GPS receivers to correct better for ionospheric delays, the major source of error in a GPS position; SBAS systems, such as EGNOS, attempt to correct this source of error too, which is introduced by the atmosphere. The new Civil GPS signals are also going to use a more technically superior code structure.

The first of the upgraded satellites are due to launch later this year.


There have been several revisions of the GPS satellites over the years. Block I satellites were the originals; all 11 have long since been shut down. Block II started with SVN12, which was a prototype and never launched, then SVN13 to SVN21 were launched, beginning in 1989 (the whole lot were launched in pretty rapid succession in 1989 and 1990). Quite a few of these satellites are still active - though they're all outside their original design life of 7 years. Block IIA was the next upgrade - the big change in these satellites is that they'll continue to work, albeit with degraded accuracy, for up to 180 days without any contact from the ground control stations. Ironically, the first of these is SVN23, the satellite that was responsible for the outage on 1 January 2004. Launches of Block IIA began in 1990 and ended in 1997.

Since 1997, the US has been launching Block IIR GPS satellites. These have various upgrades; not least a longer 10 year design life. The first Block IIR satellite gave the only GPS launch failure to date - SVN42's launcher suffered an anomaly at T+12 seconds, apparently due to a structural failure of a booster on the launch rocket, leading to the entire launcher self-destructing (think one very big and expensive bang - certainly tens of not hundreds of millions of dollars of hardware blown into tiny pieces).

2004 should see the first of a modernised series of Block IIR, Block IIR-M. The US has decided to retro-fit some of the Block IIR satellites yet to be launched with some of the forthcoming upgrades. There's an article that covers a lot of this at http://www.gps.oma.be/common/modern.html - the current signals are L1 C/A (which is what our GPS receivers use), L1 P/Y and L2 P/Y (which are the encrypted military Precise Positioning Service signals). Block IIR-M adds the new M signal to L1 and L2 - as the initial implies, this is a new military signal. It also adds L2 Civil.

L2 Civil is currently due to reach initial operating capability (18 GPS satellites equipped) in 2008, and full operating capability (24 GPS satellites equipped) in 2010. L2 Civil will allow dual frequency L1 C/A / L2 Civil receivers to operate with increased accuracy with respect to the current L1 C/A only receivers.

There's a further revision to Block II coming later on (with few details as yet) - they will be Block IIF satellites. Block IIF will add L5 Civil signals; the big change here is that they'll be in a band reserved for radionavigation which gives the signals further legal protection. This is particularly important for aviation applications.

Further on the horizon is a significant upgrade to GPS - Block III satellites.


Galileo will also improve the quality of satellite positioning - though at the moment the exact specifications of Galileo are unclear whilst the political arguments between the EU and the United States continue. I believe the US currently sees Galileo as a threat to security; they want certain aspects of the signal to be made GPS like, though I don't understand the full reasons for this (possibly something to do with the ability to carry out selective jamming). I believe that the current state is that if Galileo's designers follow the US wishes, then the US will assist them, otherwise the US will do everything in their power to obstruct them - but that may be me misreading something I don't fully understand.

The intention is that there will be multiple levels of Galileo. The lowest level will be free - and a triple or even quad Navstar GPS L1 C/A, Navstar GPS L2 Civil, Navstar GPS L5 Civil and Galileo receiver is certainly possible! There will be a more accurate commercial Galileo signal, which will be encrypted, the intention is that users can subscribe to that one. The intention is to have at least one higher encrypted level still, for military and government users only.



David

[SimonCatlin]

Well I have to say, that is the most accurate and yet readable definition of the current and future of positioning I have seen in the last five years.

As you might have gathered I have a PPL(H) and understand how GPS works and follow with great interest the advancing abilities of Highway in the Sky, non precision approaches etc...

My understanding is that Galileo (our Goolies as I saw one commentor call it) will be a different frequency and use diferent technology. European minds are thoughful that the US (and let's not forget that it is a military product) could stop GPS working at any time. We now have regular tests in the North East and in Wales of GPS jamming trials.

What P**s me off about Galileo is as a European Tax payer, this is being developed using my Sterling (or 1€45 to be precise) and yet I still have to pay to use it. No-one has suggested how this works yet, but a tax on the receivers is the most likely!
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iPhone5, TomTom, Google maps, Navfree, Viewranger and Apple Maps (ekk)

[DavidW]

[SimonCatlin]

Mentioned in Pilot magazine and NOTAMed on several occassions.

Next on I see, I'll post the link.

Thanks for the info. You have taught me more than my Garmin GPS III Pilot ever would!
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iPhone5, TomTom, Google maps, Navfree, Viewranger and Apple Maps (ekk)

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