GPS got me in (and out) of trouble.

[+Ranz]

On a recent caching run http://www.geocaching.com/seek/cache_details.asp?ID=2935 I was too busy watching my target to pay full attention to my speed. The speed limit in the area was posted 30mph, while the road size, area, and conditions would imply that it should be 35-40mph. That's just an opinion and if I had been more observant it wouldn't have mattered. End result: I received a ticket for 42 in a 30. I was pretty sure I wasn't going that fast but how could I argue. As I said, I wasn't paying enough attention.

 

When I got home I realized that my trusty MeriGold had a complete record of that journey, from my house to the cache. I loaded the tracklog into GPSTrackMaker and ran the numbers. The program told me that my average speed on that section of road was 29.1mph. I did some additional math to factor acceleration to speed and deceleration to stop and my cruising speed on that road turned out to be just under 35mph. The speed I thought I was going in the first place.

 

Armed with this information and knowing that a ticket for 12 over the speed limit would report to my insurance company, I pled not guilty.

 

The pretrial hearing was today and the prosecutor called me in to disclose the evidence against me. I explained my position without going into detail. He was intrigued and said that if I gave him a little information he might be willing to bring the violation to under 10 over the limit.

 

Maybe I shouldn't have but I was not anxious to go to trial so I laid it all out for him. I showed him the actual tracklog from the GPS. I showed him an overlay of that log on a satellite image and I showed him a close-up of the area where I was pulled over. I was honest with him and told him what I thought my actual speed was, and I showed him the calculations that gave me that result.

 

He was absolutely blown away! He said that a part of him really wanted to take this to trial just to see how it turned out because nobody had ever taken this approach on a speeding offence before. But the evidence had convinced him that my case was valid and that if I would plead guilty to 35mph he would write everything down to the minimums. I agreed.

 

When we got in front of the judge he turned in my papers and told the judge that I was pleading to a lessor charge. He then spoke to the court telling everyone that this defendant is the first one not to dispute the radar evidence, his evidence is just better.

 

I guess if I had gone to trial I stood a good chance of getting off altogether, but I was in all likelihood going 35 and I should have been more attentive. So I got what I deserved but thanks to my GPS, only what I deserved. I also gave the prosecutor and the court a highlight in an otherwise grueling day.

 

America, What a Country.....

 

[halldorr]

Very very cool

[halldorr]

Very very cool

[+clatmandu]

Hey Ranz,

That is a cool story. Probably blew away the cop too! "How'd he get all that info?"(cop )

[+clatmandu]

Hey Ranz,

That is a cool story. Probably blew away the cop too! "How'd he get all that info?"(cop )

[Night Crawlers]

Check out the ">>FLITS<< aka Speed Trapped" you can log the fact you got a ticket and get a "find" for it also! The cache is located

here or http://www.geocaching.com/seek/cache_details.asp?ID=14548 . I hope you log this one, its a great story!

 

 

FGA - Florida Geocaching Assoc.

[+infosponge]

I leave my GPS running most of the time that I'm in the car and also have wondered what would happen if I were ever stopped and I had a GPS log of my trip to use as evidence if there were any discrepancies. Thanks for the info on your experience! I very rarely speed, but every one slips up now and again.

I've always been skeptical about the overall accuracy of hand-held radar guns, and would expect a car-mounted GPS to be able to offer a counter-argument to any reading from one. Of course, there must be a +/- to the indicated speed as well, and unless your tracklock also includes a record of the EPE for each point it would be hard to know exactly what that is.

[+infosponge]

I leave my GPS running most of the time that I'm in the car and also have wondered what would happen if I were ever stopped and I had a GPS log of my trip to use as evidence if there were any discrepancies. Thanks for the info on your experience! I very rarely speed, but every one slips up now and again.

I've always been skeptical about the overall accuracy of hand-held radar guns, and would expect a car-mounted GPS to be able to offer a counter-argument to any reading from one. Of course, there must be a +/- to the indicated speed as well, and unless your tracklock also includes a record of the EPE for each point it would be hard to know exactly what that is.

[White Rabbit]

Interesting. You got pretty lucky on that one.

 

Personally I think if your speed was an average of 35mph, you could do that many ways. If you're going 42mph for 4 minutes, and 28mph for 4 minutes, your GPS would average that out at around 35mph. Though the GPS doesn't know that when you actually got radared you WERE going 42mph. Just because your average speed was less than 42mph, doesn't mean that at the time you were radared you weren't going 42mph. So I think you got off lucky and I wouldn't rely on this happening again.

 

You can correct me if I'm wrong, because I don't know exactly how your GPS tracks stuff.

 

I am the Rabbit King, I can do anything

[+Crusso]

I guess in my case I better make sure I keep erasing my Tracklog!! I had to send my gps in for repairs when I first got it because it read my highest speed attained at 123 & I knew I never maxed at more than 112!

[Khan]

When I was living in Wisconsin, I used to go geocaching on my cycle. A nice fun toy(back before some thugs in New Orleans decided to steal it on Thanksgiving) well one day I noticed that my gps unit had a current mph reading on it. Soooooooooooo I decided to see how good it was. It seemed that no matter what the speed was it was always slower than the bike's spedometer. I had the cycle over 130 that day and the gps unit said I was only going 124 I just chalked it up to the time it took to read the signal from the satellite to the cycle and gps.

[Khan]

When I was living in Wisconsin, I used to go geocaching on my cycle. A nice fun toy(back before some thugs in New Orleans decided to steal it on Thanksgiving) well one day I noticed that my gps unit had a current mph reading on it. Soooooooooooo I decided to see how good it was. It seemed that no matter what the speed was it was always slower than the bike's spedometer. I had the cycle over 130 that day and the gps unit said I was only going 124 I just chalked it up to the time it took to read the signal from the satellite to the cycle and gps.

[+Jamie Z]

Khan,

 

I'm sure the speedo on the bike was wrong. Not uncommon. The accuracy of the GPS speed is quite good.

 

Jamie

[hgmonaro]

cycle=motorcycle? (I hope.. otherwise you sure can pedal fast!!!) Car speedos are usually optimistic, maybe motorbike ones are too.

 

here in Oz, speeding is a major topic, with many handheld, mobile and fixed 'speed cameras' in use. They used to be set something like the speed limit +10% + 3kph before you got a ticket (say 69 in a 60 zone, 113 in a 100 zone), but recently they did away with the 10% bit which means their new tolerance is in fact less than the speedo accuracy required by the design rules governing vehicle manufacture. As you could gather, people are not happy!

 

Anyway, the other night on a 'current affairs' type of program, the story was about speedo inaccuracy and the story 'expert' was checking speedo's with a handheld GPS. Wonder if he geocaches on weekends!

[hgmonaro]

cycle=motorcycle? (I hope.. otherwise you sure can pedal fast!!!) Car speedos are usually optimistic, maybe motorbike ones are too.

 

here in Oz, speeding is a major topic, with many handheld, mobile and fixed 'speed cameras' in use. They used to be set something like the speed limit +10% + 3kph before you got a ticket (say 69 in a 60 zone, 113 in a 100 zone), but recently they did away with the 10% bit which means their new tolerance is in fact less than the speedo accuracy required by the design rules governing vehicle manufacture. As you could gather, people are not happy!

 

Anyway, the other night on a 'current affairs' type of program, the story was about speedo inaccuracy and the story 'expert' was checking speedo's with a handheld GPS. Wonder if he geocaches on weekends!

[+Crusso]

It just occured to me that it's way to easy to fake a tracklog for this to be admissable evidence in court. All you would have to do after getting a ticket is go back to the scene on another day, go into setup and change the date on your GPS to the date you recvd the ticket. Then run the entire route again making sure to stay under the speed limit, even pulling over where you were pulled over to make the log accurate. Then save the traclog, change the date back, take it to court and Voila.... "Your honor, look I have proof I wasn't speeding..."

[Team Dragon]

quote:

---

It seemed that no matter what the speed was it was always slower than the bike's spedometer. I had the cycle over 130 that day and the gps unit said I was only going 124 I just chalked it up to the time it took to read the signal from the satellite to the cycle and gps.

---

 

Every so often, I'll compare the GPS to the speedometer and a radar sign "You are going XX miles per hour". My yellow etrex is dead on with every sign I've seen and the car is just a hair off.

 

I'd assume the bike was off before assuming the GPS was. Propagation time is built into the algorithms used.

[peter]

quote:

---

Originally posted by Crusso:

It just occured to me that it's way to easy to fake a tracklog for this to be admissable evidence in court. All you would have to do after getting a ticket is go back to the scene on another day, go into setup and change the date on your GPS to the date you recvd the ticket...

---

 

It's not all that easy, at least not with Garmin receivers (I'm less familiar with the details of the tracklog on other brands). The date and time stamp is based on information direct from the satellites and is unaffected by anything you do in the setup menu. The times are recorded based on UTM, so changing the timezone or offset also has no effect on the recorded track data. The timestamps are only kept on the 'active log' and cannot be uploaded into the GPS rcvr., so you can't change the data on your PC and then upload an altered track.

 

There are only two ways I can think of to corrupt the active log data in the receiver:

1) hack Garmin's internal protocols to allow you to modify the active log data. I think this would be difficult given how unsuccessful people have been at creating their own maps that can be loaded into the receivers. Garmin made the active tracklog particularly secure so that it can be used to verify performance in some contests.

2) use a GPS satellite constellation simulator that sends false signals to the unit that appear to come from multiple satellites and make your GPS rcvr. seem to be travelling at a legal speed at the place and time in question. While possible, it would be very difficult and expensive to build such a simulator and program it to generate the right track log.

 

Of course if you use either of these methods in court and are discovered, then you'll be facing perjury charges instead of just a speeding ticket.

[+ClayJar]

quote:

---

Originally posted by peter:

The times are recorded based on UTM,

---

Um, not to be nit-picky or anything, but before any neocachers get confused, that was UTC, not UTM for time, right? "Universal Coordinated Time" references time, as opposed to "Universal Transverse Mercator", which references position.

 

(Of course, knowing the standard nit-picking style, I've probably made a mistake somewhere in this post, eh? )

[+ClayJar]

quote:

---

Originally posted by peter:

The times are recorded based on UTM,

---

Um, not to be nit-picky or anything, but before any neocachers get confused, that was UTC, not UTM for time, right? "Universal Coordinated Time" references time, as opposed to "Universal Transverse Mercator", which references position.

 

(Of course, knowing the standard nit-picking style, I've probably made a mistake somewhere in this post, eh? )

[CacheAndCary]

Ranz -

Resourceful use of your GPS, and an equitable settlement (though I do appreciate your temptation to go for broke.) Well done.

[+mrcpu]

I got a 93km/h in a 60km/h zone ticket and went to the "First Appearance" meeting with the procecuter. There were about 20 of us there and we each went in one at a time. When it was my turn she aske me if I was speeding. I smiled and shyly answered that I didn't think it would be wise to answer a question like that! She said "off the record" so I said that I wasn't exactly doing 60km/h!

 

She smiled and said, "How's 15 over?" (No points and a $50 ticket compared to $150) So I said SURE!!!

 

When I went into the next room there were all the other people and we all went in one at a time and plead guilty to 15 over!!!!

 

I had thought about the GPS but it would have made my position worse, not better!!!

 

Rob

Mobile Cache Command