Don't get me wrong. For me it's not a big deal.

It was just a simple question.

I'm driving like this for many years, and if you can just travel 7 miles/h (incl legal correction) faster than the rest, it makes traveling much more comfortable.

For the up/down hill correction, it's neglectible. Especially on the limited highway slopes.

Too bad LR simply forgot this item on the NAV equipment, since it is standard on any other Halfords GPS.

RRS boy AND Trots

What difference does it make to the accuracy of a GPS when you go up a hill?  Gone - 2008 Stornoway Grey RRS 2.7 TDV6
Gone - 2009 Buckingham Blue RRS 2.7 TDV6
Gone - 2010 Alaska White RRS 5.0 V8 Aspirated
Gone - 2017 Chawton White RRS 5.0 V8 Supercharged
Current - 2010 Java Black RRS 5.0 V8 Aspirated
Current- 2024 RRS P400 SE Dynamic

Pythagoras' Theorem...

Quote:

speedos are surely overstating speed to cover manufacturers

Quote:

Pythagoras' Theorem...

Does this mean that a GPS could understate your speed relative to the actual distance you're travelling on the incline, by the GPS asuming measurement of the distance you're travelling being flat?
Whilst a speed camera, whoops I meant safety camera, will measure across the actual distance travelled on the incline.
(If the above makes sense - hated Geometry, and yet one of the most useful school subjects in real life - building etc)

Regardless, there's some interesting points coming out here, lads

exactly, sat nav takes A to B1 in a straight line (distance) and calculates speed = distance/time

on a significant incline A to B2 is A greater distance, so the sat nav is underestimating distance thus giving a speed reading that's too small

B2
....\\
......\\
........\\
..........\\
............\\
..............\\
................\\
B1<<<<<< A

Excellent illustration of your point, had something very similar in my head. But it wouldn't come out of there.

This kind of incline error could be relevant in places like the Dartford Bridge. Where the Specs cameras are placed on the ascent and descent points.
If you're flirting with the limit using GPS you could come a cropper.

I don't think that hills make an appreciable difference to calculated GPS speed since GPS doesn't simply measure distance / time, it measures rate of change of position.

While groundspeed in aircraft is not usually considered a coupled flight parameter, some of our aircraft can actually use GPS groundspeed to fly an automated approach to an oil rig to a distance of 250 metres and the portion from the IAF to the FAF is in a descent and predicated on GS.

But, I see little point in getting into discussions regarding code locked loops, phase locked loops, PRRs, Kalman fliters etc and without knowing the actual internal workings of the RRS Sat Nav and how many satellites it uses, its sampling rate and processor speed (I am sure its not very clever judging by the general standard of LR electronics) it would be a waste of time anyway.

It can't even calculate a reasonable ETA!

Its probably best for Skywalker if he just drives within the speed limit! Gone - 2008 Stornoway Grey RRS 2.7 TDV6
Gone - 2009 Buckingham Blue RRS 2.7 TDV6
Gone - 2010 Alaska White RRS 5.0 V8 Aspirated
Gone - 2017 Chawton White RRS 5.0 V8 Supercharged
Current - 2010 Java Black RRS 5.0 V8 Aspirated
Current- 2024 RRS P400 SE Dynamic

BKHK,

I've drifted off SW's original topic somewhat, and am not arguing for or against his point. I agree in principle to using GPS in addtion to the speedo, which is designed to be inacurrate to a tolerance.

And think some useful info is coming out from his original question.

Would it not be fair to say that Aircraft GPS are more sophisticated than a retail car gps system, and therefore more consistently accurate?

Or is GPS a pretty standard application with little enhancement available?

Inslider

Yes, it would be fair to say that some aspects are more sophisticated. My point really is that GPS meaures the RATE of change of position over the ground and therefore calculates a groundspeed.

It does not use a simple distance / time calculation over a long enough period of time to have a large error. Sampling rates are often (not usre about the RRS) 2x per second.

Enough mind tiwsting!! Gone - 2008 Stornoway Grey RRS 2.7 TDV6
Gone - 2009 Buckingham Blue RRS 2.7 TDV6
Gone - 2010 Alaska White RRS 5.0 V8 Aspirated
Gone - 2017 Chawton White RRS 5.0 V8 Supercharged
Current - 2010 Java Black RRS 5.0 V8 Aspirated
Current- 2024 RRS P400 SE Dynamic

Gentlemen, could this be of help...?

Quote:

INTRODUCTION TO THE GLOBAL POSITIONING SYSTEM (GPS)

The system used to calculate the current position of the vehicle is called the GPS (global positioning system) . The system utilizes satellites which are owned by the United States Department of Defense (DoD). A total of 24 satellites orbit the earth every 12 hours at a height of 20,000 km (12500 miles), and between 5 and 11 of these satellites can be seen from a single point at any given time. The orbits are tilted to the earth's equator by 55 degrees to ensure coverage of polar regions. Each satellite transmits radio signals to provide information about the satellite position i.e. latitude, longitude, altitude, almanac data and an accurate time signal generated by an on-board atomic clock. Each satellite contains four atomic clocks.

The vehicle needs to receive data from at least four different satellites to give a three dimensional fix on its current position. As the vehicle moves, this information is continually being updated. The computer determines which satellites are 'visible' to the system and their current position and relationship to each other. Using this information the computer can account for positional deviations of the satellites and compensate to enhance the accuracy of the navigation system.

The GPS (global positioning system) signal is also known as the Precision Positioning Signal (PPS).

PPS predictable accuracy is:

22 meters horizontal accuracy
27.7 meters vertical accuracy
200 nanoseconds time accuracy.

Each navigation system provides computer generated audible and visual route guidance information to enable the driver to reach a desired destination. The system allows the driver to choose the desired route using minor or major roads or highways and the quickest or shortest route. Directions to hospitals, museums, monuments and hotels are also available.

The computer uses map information stored on a CD (compact disc) -ROM to determine the best route for the journey and provide the driver with details of directions and approaching junctions.

BKHK, I honestly don't know enough about this to give informed comment (As I said in my first post, "I might be wrong here, however....")

I just wouldn't feel comfortable putting my license in the hands of a device bought off the highstreet.

Some high end, professional (Military/aircraft etc) and probably prohibitively expensive piece of GPS speed equipment maybe...

Each to their own.

This is why forums are good, they provoke debate from all corners of the world and from people with varying degrees of understanding and knowledge  Runner up - 2009 Best Avatar Award
Joint runner up - 2009 Outstanding Contribution Award
WINNER - 2008 ‘Best Thread’ Award – Beautiful Women Of The World
Runner Up - 2008 Comedian Of The Year Award
Runner Up - 2008’s Funniest Incident

06 RRS TDV6 HSE, Java/Ebony, PTI, Running Boards, Privacy, S/C Grille/Vents, Stormers, Tasmods - GONE - (

Quote:

This is why forums are good, they provoke debate from all corners of the world and from people with varying degrees of understanding and knowledge

Supertrotter, totally agree.

BKHK

thanks for the info, appreciate 'mind twisting' on a subject I don't know much about.

It's impressive that something the size of your hand, can do this.

Must say though, with the GPS accuracy in Bobby's post of 22m horizontally and 27m vertically - how do they get those GPS guided bombs through the front doors of their targets

Aren't there various types of GPS though? There's the "public" system where some of the satellites are due to go out of service next year (and affect the whole satnav industry if not dealt with) but I'm sure there are other types of positioning system which resolve to greater accuracy...

Good thread this  

2009 Outstanding Contribution Award - Joint Runner Up
2009 'Tech-Head Of The Year' Award - Runner Up

Like it here? Then Donate to RRSPORT!!

Not sure about one or more GPS systems, but you could be right with a 'Public' version of the Military one, Schmoogle.

I'd read that the reason the GPS wasn't going to be supported, was that it is owned and maintained by US Military/Dept of Defence(or Offence ).
And that with the pending budget cuts, they may not support required maintenance, replace existing satelites etc.

Doesn't make much sense, as most of their kit would be deemed useless without GPS, maybe their posturing to start charging for it, if they don't already?

Unless they can allocate certain satelites between the public and military, and let the public ones go off.

Last edited by islider on Wed Oct 14 2009 8:55am. Edited 1 time in total

I think this is what I was talking about:

http://www.cellular-news.com/story/39882.php

And come to think of it, EGNOS rings a bell... I'm sure we use it here for something  

2009 Outstanding Contribution Award - Joint Runner Up
2009 'Tech-Head Of The Year' Award - Runner Up

Like it here? Then Donate to RRSPORT!!