Apology to huk finn and others

[Orient_Express]

Anyone have info on which states outlaw radar detectors? maybe a link/url.One more,,,, if a state allows them , can a town or city outlaw them within that state?

I'll be traveling from Ilinois to tennessee next week.

Firts of all, I need to aplogize to huk finn for hijacking his thread and taking it off the deep end. His question concerned only the legality of radar detectors - I expanded as I have a tendancy to do so Iggy got involved, and started a new thread here: https://www.fjrforum.com/forum//index.php?s...c=22655&hl=

It was the right thing to do as I was out of line... so I really need to apologize to both of you for that.

There is a genetic "mistake" in my family that makes me do those things and I can prove it - here's a pix of my brother Cletus. One look and you will understand.

My question is this: How accurate is GPS speed? From what I understand, most units refresh their coordinates at the rate of once per second? Is it accurate enough to keep you from getting tagged for speeding? I realize that there are ways to manipulate a GPS say anything...

 

[huk finn]

twas interesting reading/info. no offence takin here

 

[Orient_Express]

twas interesting reading/info. no offence takin here

Well.. thank you - I did not mean to mess up your post.

 

[Rogue]

My question is this: How accurate is GPS speed? From what I understand, most units refresh their coordinates at the rate of once per second? Is it accurate enough to keep you from getting tagged for speeding? I realize that there are ways to manipulate a GPS say anything...

Here is an example of what is recorded by a Garmin 276c:



Index/ Time/ Altitude/ Leg Length/ Leg Time/ Leg Speed/ Course/ Position

1 6/24/2006 1:17:17 PM 5264 ft 0.4 mi 0:00:18 83 mph 231° true N39 42 13.6 W112 12 54.1

2 6/24/2006 1:17:35 PM 5274 ft 0.4 mi 0:00:17 85 mph 231° true N39 41 59.9 W112 13 15.8

3 6/24/2006 1:17:52 PM 5252 ft 0.5 mi 0:00:21 92 mph 231° true N39 41 46.7 W112 13 36.9

4 6/24/2006 1:18:13 PM 5186 ft 0.6 mi 0:00:25 91 mph 231° true N39 41 28.9 W112 14 05.1

5 6/24/2006 1:18:38 PM 5135 ft 0.5 mi 0:00:18 93 mph 231° true N39 41 08.0 W112 14 38.0

6 6/24/2006 1:18:56 PM 5102 ft 0.6 mi 0:00:21 96 mph 230° true N39 40 52.7 W112 15 02.2

7 6/24/2006 1:19:17 PM 5092 ft 0.4 mi 0:00:17 93 mph 228° true N39 40 34.0 W112 15 31.2

8 6/24/2006 1:19:34 PM 5096 ft 0.6 mi 0:00:21 95 mph 227° true N39 40 18.6 W112 15 53.2

9 6/24/2006 1:19:55 PM 5088 ft 0.6 mi 0:00:22 96 mph 227° true N39 39 59.1 W112 16 20.8

10 6/24/2006 1:20:17 PM 5061 ft 0.5 mi 0:00:19 100 mph 227° true N39 39 38.6 W112 16 49.9

11 6/24/2006 1:20:36 PM 5034 ft 0.5 mi 0:00:20 99 mph 227° true N39 39 20.0 W112 17 16.2

12 6/24/2006 1:20:56 PM 5042 ft 0.3 mi 0:00:10 90 mph 227° true N39 39 00.7 W112 17 43.5

13 6/24/2006 1:21:06 PM 5056 ft 0.2 mi 0:00:08 82 mph 223° true N39 38 51.9 W112 17 55.9

14 6/24/2006 1:21:14 PM 5018 ft 0.2 mi 0:00:06 92 mph 210° true N39 38 44.9 W112 18 04.3

15 6/24/2006 1:21:20 PM 4990 ft 0.2 mi 0:00:08 102 mph 202° true N39 38 38.0 W112 18 09.6

16 6/24/2006 1:21:28 PM 4987 ft 0.7 mi 0:00:22 106 mph 202° true N39 38 27.0 W112 18 15.3

17 6/24/2006 1:21:50 PM 4987 ft 0.4 mi 0:00:13 104 mph 202° true N39 37 55.5 W112 18 31.5

18 6/24/2006 1:22:03 PM 4998 ft 0.6 mi 0:00:24 97 mph 202° true N39 37 37.4 W112 18 40.8

19 6/24/2006 1:22:27 PM 4995 ft 0.7 mi 0:00:26 97 mph 202° true N39 37 06.2 W112 18 56.8

20 6/24/2006 1:22:53 PM 4952 ft 0.5 mi 0:00:20 96 mph 202° true N39 36 32.4 W112 19 14.2

21 6/24/2006 1:23:13 PM 4921 ft 0.5 mi 0:00:18 97 mph 202° true N39 36 06.7 W112 19 27.5

22 6/24/2006 1:23:31 PM 4903 ft 0.4 mi 0:00:14 96 mph 203° true N39 35 43.3 W112 19 39.6

23 6/24/2006 1:23:45 PM 4892 ft 0.7 mi 0:00:25 96 mph 207° true N39 35 25.5 W112 19 49.4

24 6/24/2006 1:24:10 PM 4867 ft 0.4 mi 0:00:17 95 mph 207° true N39 34 54.6 W112 20 09.6

25 6/24/2006 1:24:27 PM 4853 ft 0.5 mi 0:00:19 100 mph 207° true N39 34 33.7 W112 20 23.3

26 6/24/2006 1:24:46 PM 4831 ft 0.7 mi 0:00:24 101 mph 207° true N39 34 09.2 W112 20 39.4

27 6/24/2006 1:25:10 PM 4810 ft 0.7 mi 0:00:26 103 mph 207° true N39 33 38.0 W112 20 59.8

28 6/24/2006 1:25:36 PM 4799 ft 0.6 mi 0:00:22 99 mph 207° true N39 33 03.5 W112 21 22.4

As you can see it recorded every 6 to 26 seconds on this section. I don't know if that is how often it samples or not.

 

[wfooshee]

I haven't used it on the bike yet, but I've used this in my car for years. I have DeLorme's Street Atlas on my iPAQ pocket PC with a Bluetooth GPS receiver that sits on the dash, and I treat its speed reading as more accurate than the speedometer in most vehicles I've used it with. Timing mile markers on the superslab gives a calculated speed right at the GPS readout. Most cars read higher than actual by 2 to even 5 miles per hour. The display for speed is updated constatly, maybe slightly more than once a second.

For the bike, I need a handlebar bracket for the iPAQ. The little GPS will velcro to anything, even sit in the tool tray under the seat. I also need a car charger wired in to keep the iPAQ alive long enough to be useful. The GPS charges through a USB-type port, just like a RAZR phone, so a RAZR charger would keep it alive forever, even though it stays up longer than the iPAQ anyway.

I'm guessing that the question comes from GPS positioning accuracy. If it only shows you within 50 feet, or 100 feet, whatever it is, how can it show you your speed with any accuracy? Well the position error stays fairly consistent from sample to sample. if you see the plot for a stretch of road, the whole plot may be 50 feet into the woods rather than on the actual road displayed. If the error was such that any point was within that circle of probability, you'd have a series of fairly disconnected points rather than a smooth, but maybe incorrect path. The error will drift with enough time, I suppose as satellites move in their orbits. Over several miles, that logged curve may cross the road a few times, or even be right on it for miles at a time.

My own unit, whether it's Street Atlas or the reveiver I can't tell, but elevation is far more prone to error than position. It seems to locate me on the world correctly, but gets my elevation badly wrong. I carried it in a plane once and was positioned the same as the on-board GPS, but at about half the altitude!

 

[Orient_Express]

Rogue,

Thanks for going to the trouble to record this and then post the info

That's some pretty good data - was your speedometer reading close to the GPS mph calculations?

 

[Orient_Express]

I haven't used it on the bike yet, but I've used this in my car for years. I have DeLorme's Street Atlas on my iPAQ pocket PC with a Bluetooth GPS receiver that sits on the dash, and I treat its speed reading as more accurate than the speedometer in most vehicles I've used it with. Timing mile markers on the superslab gives a calculated speed right at the GPS readout. Most cars read higher than actual by 2 to even 5 miles per hour. The display for speed is updated constatly, maybe slightly more than once a second.
For the bike, I need a handlebar bracket for the iPAQ. The little GPS will velcro to anything, even sit in the tool tray under the seat. I also need a car charger wired in to keep the iPAQ alive long enough to be useful. The GPS charges through a USB-type port, just like a RAZR phone, so a RAZR charger would keep it alive forever, even though it stays up longer than the iPAQ anyway.

wfooshee,

My truck is running about 4.5 mph slower that the GPS indicates, but your experience seems to be the opposite. Hmmmmm.

Just my thought, but like you, I would trust the GPS over a vehicle speedometer.

Thanks for the info...

 

[Rogue]

Rogue,Thanks for going to the trouble to record this and then post the info

That's some pretty good data - was your speedometer reading close to the GPS mph calculations?

Not a problem, that was from an old file I had uploaded from my GPS. I just had to cut & paste. My 04' speedo is usually a max of 3mph slow compaired to the GPS.

 

[Indian Scout]

Rogue,Thanks for going to the trouble to record this and then post the info

That's some pretty good data - was your speedometer reading close to the GPS mph calculations?

I have been told and it makes sense, if you were driving straight up or down a hill (if you could) your speedo would record how fast you were going. Now the question is, what would your GPS read as it is getting it's measurment from the satalite. Wouldn't it be zero?

If thats the case any upward or downward slant of the road would effect the truth of the GPS reading.

 

[Rogue]

Rogue,Thanks for going to the trouble to record this and then post the info

That's some pretty good data - was your speedometer reading close to the GPS mph calculations?

I have been told and it makes sense, if you were driving straight up or down a hill (if you could) your speedo would record how fast you were going. Now the question is, what would your GPS read as it is getting it's measurment from the satalite. Wouldn't it be zero?

If thats the case any upward or downward slant of the road would effect the truth of the GPS reading.

It also reads altitude, if you look at my post you can see the altitudes I was at. I can also show rate of altitude change.

 

[Indian Scout]

Rogue,Thanks for going to the trouble to record this and then post the info

That's some pretty good data - was your speedometer reading close to the GPS mph calculations?

I have been told and it makes sense, if you were driving straight up or down a hill (if you could) your speedo would record how fast you were going. Now the question is, what would your GPS read as it is getting it's measurment from the satalite. Wouldn't it be zero?

If thats the case any upward or downward slant of the road would effect the truth of the GPS reading.

It also reads altitude, if you look at my post you can see the altitudes I was at. I can also show rate of altitude change.

On my 2610 it reads MPH. Are you telling me that it calculates off both distance and altitude to get the correct speed?

 

[HaulinAshe]

You can see a noticeable difference in the updates on the Zumo, based on how much map detail you have selected. With map resolution set to LOW, it updates almost as fast as a digital cager speedo. But at HIGH, it can be 20 seconds or more between speedo updates. I can make a BIG change in speed inside of 20 seconds on the FEEJ.

 

[Rogue]

On my 2610 it reads MPH. Are you telling me that it calculates off both distance and altitude to get the correct speed?

I have no idea.

On the 276c three of the available displays on the trip computer page are (this taken from the on line manual https://www8.garmin.com/manuals/GPSMAP276C_OwnersManual.pdf . page 117):

Elevation-the altitude (height) above or below mean sea level (MSL).

Speed-your current vehicle speed can be measured in miles per hour, kilometers per hour or knots.

Vertical Speed- the rate of climb or descent.

 

[wfooshee]

Any two adjascent points are 3D coordinates, with a known distance between them. The time elapsed between them is also known. Speed calc is basic arithmetic, and slope is irrelevant.

That said, the speed display on mine is more of a moving average, I think. Grab some brake, it takes the device a couple of seconds to get down to my actual speed.

edit: Of course I'm making an assumption here, that the 3D coordinates are used and not the 2D for speed calc. Even so, the error would be minimal except for hillclimbs and trials, and I don't think Feejers do that. I'll get my trig tables out and see. Someday.