GPS and policeman question

[cowboyz]

ok. So I got meself a GPS for the bike. Great things they are too. Now I always know where I am.

I actually got it for the recording functions of it like top speed, avg speed, distance travelled and things like this.

Not the question is .. If I get pulled over doing say 120 and Mr policeman sees my GPS reading a top speed of 160ish can he book me for it?

[thehollowmen]

Not really

Claim you went to a track day and haven't reset the stats yet.

he ain't likely to go and find out where you did 160 km/h (digging in the GPS records), and it ain't a certified measurement device for their records..

[Jantar]

He can't use it unless you intend to use the data to defend a ticket. Once you introduce the record as evidence then the court can ask to see the entire record. Remember that part of the record includes timestamp and location, so only use GPS if you are sure that the entire record will support your case.

[Indoo]

ok. So I got meself a GPS for the bike. Great things they are too. Now I always know where I am.

I actually got it for the recording functions of it like top speed, avg speed, distance travelled and things like this.

Not the question is .. If I get pulled over doing say 120 and Mr policeman sees my GPS reading a top speed of 160ish can he book me for it?

He can't and he won't, and didn't you do that on that private racetrack you were on a few hours prior?

[cowboyz]

that is good then. pretty unlikely but with my luck you never know. Even down to a checkpoint as the GPS is in clear view and the numbers are right there. I dont want to be scrambling to turn it off looking dodgy to have them check the unit for what I was doing on the back roads.

[Insanity_rules]

Yep they aren't allowed to look thorugh it. On a seperate question are they accurate for speed and location?

[GR81]

Hmm it could be viewed as being personal information, that is hes not really entitled to look at it without a warrant...same as your not allowed to have your cellphone gone through.
how would you know? arent you a school janitor? *cough* hahaha :rofl:

[sAsLEX]

Yep they aren't allowed to look thorugh it. On a seperate question are they accurate for speed and location?

yes and no, if they have a few sats in view yes, but in urban environments you get problems, but that said they will put you accuratly within a few meters most of the time on the open road and the speed is more likely more accurate than your speedo

[MisterD]

yes and no, if they have a few sats in view yes, but in urban environments you get problems, but that said they will put you accuratly within a few meters most of the time on the open road and the speed is more likely more accurate than your speedo

I wouldn't necessarily trust them for instantaeous speed, but for an average they're pretty good. As sAsLEX says, in urban environments they can be tricky as they'll be picking up signals reflected off buildings as well as direct so if you were to plot the reported position you will see some sideways jumps and stuff.

What type have you got?

[sAsLEX]

I wouldn't necessarily trust them for instantaeous speed, but for an average they're pretty good. As sAsLEX says, in urban environments they can be tricky as they'll be picking up signals reflected off buildings as well as direct so if you were to plot the reported position you will see some sideways jumps and stuff.

What type have you got?

actually the signals associated with GPS have mechanisms in them to ignore reflected signals

[MisterD]

actually the signals associated with GPS have mechanisms in them to ignore reflected signals

They try, but "multipath" is still one of the biggest headaches for GPS systems in urban areas.

[igor]

seize it as an exhibit.

[sAsLEX]

They try, but "multipath" is still one of the biggest headaches for GPS systems in urban areas.

A bigger headache is signal drop out completly, they have done urban location using cell phone tech but obviously that wont work in hostile terrirtory, best bet is an Inertial NAv unit that updates when GPS is in range :msn-wink:

[madboy]

Aside from questions of whether the police have the right to obtain or use the information from the GPS unit, they would also need to prove that the unit was attached to your bike at the time that reading was taken.

Ask Skelstar what would have happened had he been pulled after his GPS arrived back on his old Hyosung 250 with 230k as the top speed. Do you seriously think it could have been done on that bike, your honour?

[cowboyz]

it is a garwin etrex el-cheapo unit from DSE. $230. Records paths, top speed , avg speed overall, avg speed while moving, distance, ETA on waypoint, Expected time of arrival at waypoint. Can store 100 or so waypoints or something. More than I need. It doesn't have a map or anything so you cant ask it where a town is but that just seemed pointless to me as they measure the distance as the crow flys which is alot shorter than any route I am going to take. Seems as accurate as my car speedo and my bike speedo is about 7k out on the high side. Using it for cheating at golf to tell me how far the away the green is and it seems to be bang on. I am really happy with the unit for a cheap one.

[imdying]

A bigger headache is signal drop out completly, they have done urban location using cell phone tech but obviously that wont work in hostile terrirtory, best bet is an Inertial NAv unit that updates when GPS is in range :msn-wink:Apparently the European system Galileo will work indoors etc, as well as being more accurate... bet the americans love that :laugh:

[Patrick]

how would you know? arent you a school janitor? *cough* hahaha :rofl:

And seller of flowers...but sshhhhh.... thats secret...

[sAsLEX]

Apparently the European system Galileo will work indoors etc, as well as being more accurate... bet the americans love that :laugh:

How got any info on it? They are geosynchrounous aint they those ones?

edit, No sAs they are MEO orbiting constellation of 30 sats, 3 spare, designed for civilain use

[imdying]

Heaps of white papers on the net about them, pretty sure they EU have a big site on it somewhere.

[lb99]

Let me foigure this out....
so your GPS snds out a signal saying "where am I?", and the satellites figure it out and reply "you are (Here)", ... is that right?


If so then isn't it possible that the sattelite is recording your position each time you query it? thus tracking your movements!!!:eek5:

Is this possible?

Should I start final preperations?

[imdying]

Nope, nothing like that son :)

[ajturbo]

Let me foigure this out....
so your GPS snds out a signal saying "where am I?", and the satellites figure it out and reply "you are (Here)", ... is that right?


If so then isn't it possible that the sattelite is recording your position each time you query it? thus tracking your movements!!!:eek5:

Is this possible?

Should I start final preperations?

you think tooo much... i hope:mellow:

[sAsLEX]

Let me foigure this out....
so your GPS snds out a signal saying "where am I?", and the satellites figure it out and reply "you are (Here)", ... is that right?
Should I start final preperations?

The sats send out an L1 and a L2 sig which are encoded radio signals, in this it sends GPS time, the exact location the satallite is in , the vauge area the satilites will be in for the next week or so and some other stuff. It has a rather complex code that is sent in the signal to tell all that stuff and sync your reciever.

L1 => s(t)=SQRT(2*Pi)d(t)c(t)cos(wt + phi) + SQRT(2*Pq)d(t)p(t)sin(wt+phi)

Pi and Pq are respective carrier powers
d(t) is the 50 bps data modulation
c(t) and p(t) are a C/A and P pseudorandom code wavforms
w is the L1 carrier freq
Pq is 3dB less than Pi

L2=> s(t) SQRT(2*Pq) d(t)p(t)sin(wt+phi)

fun eh?
When you turn on your reciever it remebers the vauge info of the last sats it seen and searches for those that should be visible, its kinda neat that all the sats transmit on the same freq, and once recieving sat signals the reciever works out the delay from each one, and with some of the atmospheric data transmitted in the signal it works out the distance to each sat in view.

Once it has that it can calculate your position to 10 m accuracy or so.

[Lou Girardin]

A guy in ChCh used GPS data to defend a speeding ticket. He succeeded.

[MisterD]

The sats send out an L1 and a L2 sig which are encoded radio signals, in this it sends GPS time, the exact location the satallite is in , the vauge area the satilites will be in for the next week or so and some other stuff. It has a rather complex code that is sent in the signal to tell all that stuff and sync your reciever.


If you don't mind me adding some to that sAsLEX....

The signal the satellite sends is unique and and repeats over a pretty long time frame (think wallpaper with a really long repeat on the pattern). The receiver knows what the pattern is (ie has a wallpaper sample) and basically slides it up and down past the received signal to match it up (a process called "correlation") by this means the receiver can work out the time delay and therefore the distance to the satellite.

Distance from 3 Sats will give you 2D and 4 will give you 3D position...

[MisterD]

Apparently the European system Galileo will work indoors etc, as well as being more accurate... bet the americans love that :laugh:

It'll work indoors becuase they're trying to bump the power of the transmitted signals up, as for more accurate that's not particularly relevant as the two systems are mandated to be compatible so you'll have more accuracy because receivers will be using both systems at once and you'll always have more satellites in view.

GPS will work indoors if you've got a good enough timing reference in your receiver and a chipset that'll make use of it. SiRF Star III is the current standard setter if you want to not get lost on the way back from the lav...

The important thing is, can you store "Points of interest" ie speed cameras?

[sAsLEX]

If you don't mind me adding some to that sAsLEX....

The signal the satellite sends is unique and and repeats over a pretty long time frame (think wallpaper with a really long repeat on the pattern). The receiver knows what the pattern is (ie has a wallpaper sample) and basically slides it up and down past the received signal to match it up (a process called "correlation") by this means the receiver can work out the time delay and therefore the distance to the satellite.

Distance from 3 Sats will give you 2D and 4 will give you 3D position...



yeah the C/A code with a 1023 chip sequence and a period of 1ms and a chipping rate of 1.023MHz

the P code is similar and has a period of a week and is used for mainly military options

[sAsLEX]

The important thing is, can you store "Points of interest" ie speed cameras?

some of the top model radar detectors come with GPS and a database of all the known fixed speed cameras and give you advanced warning

[GR81]

And seller of flowers...but sshhhhh.... thats secret...
what was Maxwell Smart? a greeting card salesman or something?
bwhaha i loved that show!

[Biff]

If I was a copper I'd book you. Not for speeding, but for having a wanky widget.

Lucky git.