Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Tony H]

GPS measures nothing, it just gives a 3D position in space, relative to the sattelites received

It is how it is mapped and reported by the inbuilt algorithms that matters. Military GPS can hardly be considered "cheap", especially when overlaid on a military standard terrestial map database.

Put these together and an extremely accurate 3D position is obtained...position and height.... not quite in the same ballpark as Mr TomTom & Mr NavTeq who can't even get roads in the right place ..let alone the hills !!!

[/highlight]
It was even more fun when the powers that be in the American military used selective avaiability!!

[Debs.]

GPS measures nothing, it just gives a 3D position in space, relative to the sattelites received

It is how it is mapped and reported by the inbuilt algorithms that matters. Military GPS can hardly be considered "cheap", especially when overlaid on a military standard terrestial map database.

Put these together and an extremely accurate 3D position is obtained...position and height.... not quite in the same ballpark as Mr TomTom & Mr NavTeq who can't even get roads in the right place ..let alone the hills !!!

[/highlight]
It was even more fun when the powers that be in the American military used selective avaiability!!

Oh gawd yes!....I remember back in 1989 during a extended-flight in my li`l plane in the U.S; my GPS position 'jumped' 10 miles North of my chart D.R (actual) position and remained grossly inaccurate for the rest of the flight......back then civillian GPS was an aviation 'toy' because the Military kept it inaccurate/unpredicable.  :-/

[robby30]

Other side of the road buddy.  I drive for a living (around 300+ miles a day).  At the weekend part of my run is from Berwick to Edinburgh and the cameras on the other side of the road flash too late to catch you.  Very few cameras can catch you face on (in fact don't think any do).  The lines on your side of the road aren't for catching you they are for catching cars overtaking on the other side.

The truvello cameras take your snap from the front, they have more discrete markers on both sides of the road and the camera is able to get you from the other side. they are easy to spot as in most forces they are blue and yellow instead of grey and yellow
And they are set at 35mph if they have film in.
by the way this week is Tispol (european police) speed enforcement week, im sure that my force is not the only one doing extra checks for it
At least its sunny for us

[prestigesec]

Play the paper chase with them asking for all kinds of information which they have to give to you and in the end they will get bored and not have the man power to produce the information needed to support there case. Its not hard just takes a little time and effort on your behalf, dont roll over and take it up the **** its your licsence protect it, i do and have 0 points!!!

[Tony H]

GPS measures nothing, it just gives a 3D position in space, relative to the sattelites received

It is how it is mapped and reported by the inbuilt algorithms that matters. Military GPS can hardly be considered "cheap", especially when overlaid on a military standard terrestial map database.

Put these together and an extremely accurate 3D position is obtained...position and height.... not quite in the same ballpark as Mr TomTom & Mr NavTeq who can't even get roads in the right place ..let alone the hills !!!

[/highlight]
It was even more fun when the powers that be in the American military used selective avaiability!!

Oh gawd yes!....I remember back in 1989 during a extended-flight in my li`l plane in the U.S; my GPS position 'jumped' 10 miles North of my chart D.R (actual) position and remained grossly inaccurate for the rest of the flight......back then civillian GPS was an aviation 'toy' because the Military kept it inaccurate/unpredicable.  :-/

When the first gulf war started the yanks stopped using S.A the result was our gps accuracy changed from a typical 90 metre accuracy to less than 5 metres we where made up as it made finding shipwrecks a lot easier

[Humpy]

Sorry to put a downer on it mate but if the vehicle is a company vehicle or hire/lease vehicle the fourteen day limit doesn't count. I work for, shall we say the biggest comms company in the UK, and my ticket turned up two months after the event Bummer.

Humpy

[Gaffers]

GPS speed is highly accurate under CERTAIN CIRCUMSTANCES. GPS will measure the time between two points in 3 dimensional space to a high degree of accuracy... the problems are :

1. GPS makers do not tell us what the time interval is - so we have to assume it is quite small - The larger it is the bigger the errors that :

2. GPS works in straight line in 3D, so if you are on a bend, or a hill then you will have an error ( draw your "true" path on a piece of paper to see what I mean)

3. GPS cannot take acceleration or deceleration into account .. it works purely on the total time and total distance between sampling points.

4. A minimum of 4 good satellite signals must be present throughout the sampling period.

So .. if you are on a dead level, dead straight road, driving at a constant speed in an exactly straight line, throughout the (unknown) sampling period, with good satellite coverage, ... then your SatNav will give a good indication of your true speed.

Note the "dead level" requirement .... the surface of the earth curves ....  

(the last comment is slightly facetious ... the difference caused by the earth's curvature is negligible ... but hills DO make a difference ..)    

Not to good on altitude either, the gps on my boat will often give an altitude figure of up to 65 feet

Gar! A fellow sailer!  Good to meet ya!  

[Kevin Wood]

GPS altitude uncertainty is (I think) a factor of 3 greater than the horizontal position. Because it's often obvious what your altitude is, it highlights the error.

As mentioned, GPS tells you your position relative to some chunks of metal orbiting the earth and knows nothing of the earth's surface. It has a model of the earth's surface which is used to estimate your position relative to the earth's surface and express it in longitude, latitude and altitude. On most GPS you can select the model it uses.

When you consider it's triangulating between satellites 12,600 miles away orbiting the earth twice a day, an error of 65 feet is put into perspective.  8-)

I was testing a GPS mapping system for mobile phone coverage in the early 90's and couldn't believe that when I had taken a drive, the trace of where I had been overlaid perfectly onto a 1:25K OS map. I'm not sure whether I was more impressed with GPS or the OS map. I later found out that SA had been turned off.

Incidentally, I spent a week on this project and got all the kit installed in a survey van and working perfectly. Customer picked it up and promptly put it on its' roof on the way home.

Kevin

[Debs.]

.....Customer picked it up and promptly put it on its' roof on the way home.
Kevin

  Jeeesh!...there`s just no helping some folks is there?  

[Gaffers]

.....Customer picked it up and promptly put it on its' roof on the way home.
Kevin

  Jeeesh!...there`s just no helping some folks is there?  

Are you sure the Sav Nat didn't 'Flip car over here' ?