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DISCO3.CO.UK > Faults & Fixes (D3)

[Software] Sat Nav Altimeter
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Martin
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Member Since: 06 Nov 2004
Location: Hook Norton
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Wales 2006 Discovery 3 TDV6 SE Manual Buckingham BlueDiscovery 3
Sat Nav Altimeter

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
  
Post #5693rd Feb 2005 8:56 am
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Ecosse
 


Member Since: 07 Jan 2005
Location: Grampian, Scotland
Posts: 856

2012 Discovery 4 3.0 TDV6 HSE Auto Unknown ColourDiscovery 4

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
  
Post #91121st Feb 2005 1:29 pm
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hvilorio
 


Member Since: 24 May 2005
Location: Santo Domingo
Posts: 9

Dominican Republic 2010 Discovery 4 3.0 TDV6 HSE Auto Zermatt SilverDiscovery 4

Mine is the opposite, it will show -30 meters at sea level, is there any way of fixing this?
  
Post #264196th Nov 2005 5:42 am
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draughtsman
 


Member Since: 26 Sep 2005
Location: Hereford:- Handy for Eastnor
Posts: 51

United Kingdom 2013 Discovery 4 3.0 SDV6 XS Auto Orkney GreyDiscovery 4

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 Confused
  
Post #270719th Nov 2005 7:32 pm
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Gareth
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Member Since: 07 Dec 2004
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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 Confused


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 Wink
  
Post #270889th Nov 2005 8:01 pm
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Pelyma
  


Member Since: 06 Jan 2005
Location: Patching, Sussex
Posts: 10765

England 2016 Discovery 4 3.0 SDV6 HSE Lux Auto Montalcino RedDiscovery 4

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 Confused


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.
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Post #270919th Nov 2005 8:10 pm
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espri
 


Member Since: 07 Nov 2005
Location: Tyrol, Austria
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Austria 2006 Discovery 3 TDV6 HSE Auto Arctic FrostDiscovery 3
Re: GPS accuracy

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
  
Post #271789th Nov 2005 9:43 pm
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W6CJW
 


Member Since: 06 Nov 2005
Location: Sunny Sussex
Posts: 76

United Kingdom 2010 Discovery 4 3.0 TDV6 HSE Auto Zermatt SilverDiscovery 4

Hmmmmmm my father in law has a Garmin hand held gadget that is spot on Question We checked it against an os map last week in Wales. The Garmin gadget read 150+ and yes guess what D3 350+ Surprised . 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 Question as the Garmin gadget also uses satalites Very Happy or is it more dodgy LR software Laughing
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Post #2728810th Nov 2005 1:45 pm
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djheaton321
 


Member Since: 18 Sep 2005
Location: Northamptonshire
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United Kingdom 2007 Discovery 3 TDV6 HSE Auto Stornoway GreyDiscovery 3

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. Cool
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Post #2731710th Nov 2005 4:03 pm
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Winger
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Member Since: 15 Feb 2005
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And, of course, atmospheric conditions play a part in it too.
  
Post #2731810th Nov 2005 4:06 pm
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lee01277
 


Member Since: 06 May 2005
Location: Shed
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United Kingdom 2005 Discovery 3 TDV6 S Auto Zambezi SilverDiscovery 3

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 
Post #2732110th Nov 2005 4:29 pm
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Winger
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Member Since: 15 Feb 2005
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No there isn't.
  
Post #2732410th Nov 2005 4:56 pm
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djheaton321
 


Member Since: 18 Sep 2005
Location: Northamptonshire
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United Kingdom 2007 Discovery 3 TDV6 HSE Auto Stornoway GreyDiscovery 3

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
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Post #2732810th Nov 2005 5:43 pm
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Winger
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Member Since: 15 Feb 2005
Location: UK
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2016 Discovery 4 3.0 TDV6 HSE Auto Aintree GreenDiscovery 4

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.
  
Post #2733410th Nov 2005 6:04 pm
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PJ
 


Member Since: 19 Oct 2005
Location: East Sussex
Posts: 52

England 

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.
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Post #2733910th Nov 2005 6:12 pm
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