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Martin
Site Admin and Owner
Member Since: 06 Nov 2004
Location: Hook Norton
Posts: 18573
  
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- Classification
- Fault electrical/software
- Problem
- Sat Nav altimeter overstates height eg 500 ft when actually 300 ft
- Affected vehicles
- Sat Nav equipped
- Reported
- 7th January 2005 by Ecosse in post 93
- Reported Cases
- 2
- Occurs
- Constant issue
- Submitted to dealer network
- Yes
- Dealer Response
- To refer to LR
- Submitted to LR Customer Services
- Yes
- LR CS Response Reported
- They will liase with dealer
- Fix/Solution
- None
- Other Comments
- None
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 3rd Feb 2005 8:56 am |
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Ecosse
Member Since: 07 Jan 2005
Location: Grampian, Scotland
Posts: 892
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LR CS advise that there is no fix yet! ie it is a feature that does not work properly! They have yet to revert with a timescale to fix
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| 21st Feb 2005 1:29 pm |
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hvilorio
Member Since: 24 May 2005
Location: Santo Domingo
Posts: 9
  
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Mine is the opposite, it will show -30 meters at sea level, is there any way of fixing this?
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| 6th Nov 2005 5:42 am |
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draughtsman
Member Since: 26 Sep 2005
Location: Hereford:- Handy for Eastnor
Posts: 51
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I'm sure i read somewhere that the altitude reading on sat nav systems is deliberatley inaccurate due to possible terrorist use.
i.e two signals in use.
a) US military scrambled is accurate.
b) General purpose signal for Say Nav systems with altitude set inaccuratley.
I can't remember where this came from though 
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| 9th Nov 2005 7:32 pm |
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Gareth
Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26779
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draughtsman wrote:I'm sure i read somewhere that the altitude reading on sat nav systems is deliberatley inaccurate due to possible terrorist use.
i.e two signals in use.
a) US military scrambled is accurate.
b) General purpose signal for Say Nav systems with altitude set inaccuratley.
I can't remember where this came from though
The altidude is determined by information on the base map, not detrmined from the satellites. The sats only enable the system to determine where you are. The altitude at any given point is a result of the info on the map dvd.
The only way to fix this will be to replace the nav dvd with one that has got correct altitude info on it. This is about as likely to happen as Stockport County to win the FA Cup 
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| 9th Nov 2005 8:01 pm |
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Pelyma
Member Since: 06 Jan 2005
Location: Patching, Sussex
Posts: 15496
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draughtsman wrote:I'm sure i read somewhere that the altitude reading on sat nav systems is deliberatley inaccurate due to possible terrorist use.
i.e two signals in use.
a) US military scrambled is accurate.
b) General purpose signal for Say Nav systems with altitude set inaccuratley.
I can't remember where this came from though
Yes GPS is intentionally innaccurate although I believe DGPS is more accurate our US cousins, who developed the system, were sensible enough to prevent the rest of the world turning it against them too accuratley. DS3 TDV6 HSE - Silver with Alpaca (old one) Gone
DS3 TDV6 HSE- Silver with Alpaca (new one) Gone
D4 HSE Lux - Montalcino Red Gone
Porsche Cayenne V8 Diesel S
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| 9th Nov 2005 8:10 pm |
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espri
Member Since: 07 Nov 2005
Location: Tyrol, Austria
Posts: 387
 
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My understanding (from sailing magazines) is that the deliberate inaccuracy, which the US miltary wanted in GPS, was switched off a year or two ago, so that the maximum accuracy is now generally available. However, reception problems can always lead to some temporary loss of accuracy. DGPS does provide further accuracy.
Eric
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| 9th Nov 2005 9:43 pm |
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W6CJW
Member Since: 06 Nov 2005
Location: Sunny Sussex
Posts: 81
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Hmmmmmm my father in law has a Garmin hand held gadget that is spot on  We checked it against an os map last week in Wales. The Garmin gadget read 150+ and yes guess what D3 350+  . I live near Shoreham-by-sea and have parked on the beach and still it read 300+........well the tide was in!
Has this put a spanner in the works regarding the satalite issue as the Garmin gadget also uses satalites  or is it more dodgy LR software  D4 3.0 HSE cameras,Hybrid TV, 20" alloys, heated wheel, privacy, Tow pack.
Departed RRS TDV8 HSE Full Arden kit in TEAL and colour coded everything.
Departed Disco 3 2.7 HSE
I never drive faster than I can see!
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| 10th Nov 2005 1:45 pm |
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djheaton321
Member Since: 18 Sep 2005
Location: Northamptonshire
Posts: 45
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The US military used an extra signal to filter out inaccuracies in the other signals which meant that it was never more than a few hundred metres accurate. This signal was opened to civilian use a couple of years ago, I think it was something to do with the freedom of information act and the fact that there was some perceived competition with the russian glonass system and the upcoming eu galileo system. It is very accurate, but not more than 100 metres (officially). DGPS is slightly different in that it uses a ground based transmitter to further improve accuracy. The principle use of it is in aviation, the idea being that the ground based transmitter is put on the airfield and aircraft equipment uses this and the satellites to get a fix to within metres and fly very accurate approaches in poor weather into airfields that at the moment they would not. The military uses visual maps programmed into its cruise missiles to achieve that same accuracy, another idea that is under development in the aviation world. WRT altitude data, 300ft is not that inaccurate in reality. The altitude data is from the gps, not from the disc. I have seen two very high grade gps receivers differ by a few hundred feet regularly under perfect reception conditions which you don't often get in the uk at ground level position. GPS is not as accurate as a lot of people seem to think it is, try parking on your drive and setting it as a memory point, it will be stored in the computer as the lat and long at that point. Now watch that point move around over the next few weeks. 8) Discovery 3 TDV6 HSE
Defender 90 XS - now with a Webasto FBH that works!
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| 10th Nov 2005 4:03 pm |
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Winger
Site Moderator
Member Since: 15 Feb 2005
Location: UK
Posts: 3428
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And, of course, atmospheric conditions play a part in it too.
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| 10th Nov 2005 4:06 pm |
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lee01277
Member Since: 06 May 2005
Location: Shed
Posts: 821
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Winger wrote:And, of course, atmospheric conditions play a part in it too.
SA ( Selective Availability ) was switched off a number of years ago by uncle sam, which meant that joe public could use their little hand held’s to with 10 meters or better, rather than 100 feet or so it was before hand. There is only one GPS public system, and as uncle sam doesn’t charge, he can do what he likes with it.
Ref Altitude, usually on hand held’s you decide if its 2d or 3d, and if 3d, you need to tell it where the ground is by ideally re-setting by sea level (when at the beach ...). Same goes if you travel more than about 300 miles without the hand held switched on, you need to re-calibrate. And even more so if you switch continents... don’t expect it to lock on with any speed, if at all until you have re-set.
My point is, is there a re-calibrate function (I’ve an S and use TOMTOM) on the D3 sat nav to tell it where sea level is? ..............Somewhere in-between my old D3 and what's to come next .........
Last edited by lee01277 on 10th Nov 2005 10:30 pm. Edited 1 time in total
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| 10th Nov 2005 4:29 pm |
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Winger
Site Moderator
Member Since: 15 Feb 2005
Location: UK
Posts: 3428
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No there isn't.
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| 10th Nov 2005 4:56 pm |
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djheaton321
Member Since: 18 Sep 2005
Location: Northamptonshire
Posts: 45
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All you need is four satellites for a 3d fix, there should be no need to callibrate the receiver for altitude. One of the reasons for recallibrating when the unit has either not been used for a long time or has been moved a long distance since it was last switched on is to aid positon acquisition, if it knows where it is in the first place, it knows the best satellites to look for. it is not uncommon for the system to take quarter of an hour or so to generate a position, though things seem to be improving on the later receivers. The land rover system, along with other manufacturers uses an electronic compass together with data from the abs sensors (for wheel speed) and a rudimentary inertia sensing system so that when the gps signal is lost (which is a lot more often than you realise) the system still has some idea of where it is. These pages do quite a good job of explaining how gps works:
www.pocketgps.co.uk/howgpsworks.php
www.nasm.si.edu/exhibitions/gps/work.html Discovery 3 TDV6 HSE
Defender 90 XS - now with a Webasto FBH that works!
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| 10th Nov 2005 5:43 pm |
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Winger
Site Moderator
Member Since: 15 Feb 2005
Location: UK
Posts: 3428
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The reality is, of course, that the D3 is a land based mode of transport, and that altitude is more for general information than anything else.
LR have admitted that their system is off vertically, but vertical GPS measurements have always, at the consumer level, been less accurate than horizontal measurement. Calibrating vertically is complex. How many people really know their true height about WGS-84? Add to that, to get a significantly accurate vertical measurement, you really need to have a satellite directly overhead, and to be able to receive a signal from a satellite beneath you.......which, of course, presents you with a difficulty.
Long and short, in the in-car application, vertical accuracy is always going to be questionable (even on a boat you don't necessarily know where true sea-level is - that'll get the brain cells churning) and LR know that there is a system fault too.
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| 10th Nov 2005 6:04 pm |
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PJ
Member Since: 19 Oct 2005
Location: East Sussex
Posts: 52
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Hi guys, thought I would add my pennyworth here. GPS sytem is now pretty accurate on a daily & yearly basis within say 3m in my experience & is not notably effected by atmospherics but this does depend on the quality of receiver & your fix on satelites, as previous post have said prior to the wobble being deselected it was pretty useless & no better than the old Decca system we used (but we new when they were starting operations in Iraq as the us would take out the wobble, there was a shortage of hand held units for the troops so had to use non milatry units) hence the introduction of differential GPS which was brilliant when working. Trouble is the differential signal was effected by weather & the like as it relied on a few low powered land based staions dotted about uk coast & europe transmitting on different frequencies which could mean switching the receiver to another station when out of range. The basic gps signal is that good now that I don't bother to use the differential signal, however the accuracy used for surveying is something else & in the uk they use a different satelite system (not the US one) which is on subscription & I beleive the company is based in Cambridge that operate it, the accuracy is down to many decimal places.
As for the altitude, well our marine units have a setting for the input of height above sea level of antena as this obviously effects the accuracy of position fixing, one could assume therefore that accuracy of the units in our motors must vary according to altitude as it appears they are not fitted with altitude meter but how they are set up, I don't have a clue.
Do we need the French system as well?, think I would rather trust the yanks. TDV6 2004 Auto Zambezi Silver Badged SE not quite an S with Nav & Rear DVD
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| 10th Nov 2005 6:12 pm |
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