GPS readings, true or false!

[Fluid]

Every single GPS reading I have taken while running the traps at SAW events has been within 4 mph of the trap speed. Most were much closer. That is about 50 data points. Perhaps I just got lucky and acquired plenty of satellites each run.

IME radar is very poor for obtaining reliable speeds. The main reason is the angle on the item being tracked. Unless the angle is pretty close to head-on, the readings will be inaccurate. Again confirmed during SAW events. But the biggest discrepancy I saw was the year Joerg set the FE record at 120 mph. A highway patrol officer was positioned at the very end of the course and was reading parallel to the vector of travel. He read 142+ mph. Was that wrong? Maybe not, since the traps record the average speed, while the radar records the maximum speed. Joerg's rigger was clearly accelerating through the traps, so it is possible he did reach 140 long before he actually set the official record at that speed.

There is a reason why records are set - boats, cars, models and full scale - by running the vehicle through timing traps. No other method has the accuracy level to use to determine a world record.


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[Jeepers]

by running the vehicle through timing traps. No other method has the accuracy level to use to determine a world record.
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I wonder if you can use that argument to get out of a speeding ticket.

sorry officer but your radar gun just is not accurate enough, If you want I could go back and you can set up a timing trap and measure my average speed!!

[Jeff Wohlt]

When we started seeing cf boats at the shoot out the radars had issues getting speeds so they put red reflectors on the boat so the radar could lock on..miss bud was the first cf we saw there

[Fluid]

I wonder if you can use that argument to get out of a speeding ticket. sorry officer but your radar gun just is not accurate enough

Laugh all you want, but plenty of attorneys in Texas get their clients off with exactly that argument. In other states they argue that speed traps only give an average speed and rely on the officer hitting the stopwatch at the right time, so they are not accurate. This all has much more to do with revenue generation than with speed measurement, it has no relevance to this thread.



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[NativePaul]

May well be able to it, was successfully argued over here many years ago and radar traps are no longer admissible evidence here and havent been for many a year, certainly since I started driving, in our speed traps the radar just triggers the trap which takes 2 photos a set time apart and graduated markings at the side of the road show how far you went during that time, like a SAWS trap in reverse.

[Brushless55]

Any GPS readings I post are confirmed with at least 3 runs. Plus the GPS is usually on in the car on the drive to the pond so I can see if its close to my car's speedo.

The purists will say that unless its a formal SAW type of set up for recording speeds, GPS's can't be relied on, but for me, its close enough as a few MPH here or there is pretty minor.

runing 2 to 4 runs just to make sure is how I do it

That's why I use both gps and radar for backup confirmation

I got my Bushnel this week!

[jingalls007]

That's why I use both gps and radar for backup confirmation

Good, then bring it to the lake tomorrow cause I'm finished with the H&M M-1... It hauls a$$ Chris..

[LiPo Power]

Going arround small pond high speed will also read wrong speed. Runs have to be straight and long for gps to reas correctly, if possible. I know this may be very challenging for some of us but all this funky GPS systems are not accurate for a reason....
Get on the bike with GPS and do circles on the parking lot fast you will see your reading will go off the wack...
just my 3 canadian cents...

[H2OCamel]

Good, then bring it to the lake tomorrow cause I'm finished with the H&M M-1... It hauls a$$ Chris..

You Got it mate! I'll bring video and still camera too! I hope the weather is good.

[Jeepers]

Laugh all you want, but plenty of attorneys in Texas get their clients off with exactly that argument. In other states they argue that speed traps only give an average speed and rely on the officer hitting the stopwatch at the right time, so they are not accurate. This all has much more to do with revenue generation than with speed measurement, it has no relevance to this thread.

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Dude, it was a joke and a lame one at that......... In my younger days I have had my share of attorneys and tickets, I know the revenue game. street racing will do that to person..... lot of trouble real fast, empty wallet even faster.

Jay you have already posted the best way to measure speed, timing traps..



IME running GPS in model boats, the longer the run the more accurate they seem, I have seen some very misleading readings as well, thats why I know longer post GPS speeds at all.

a couple of years ago a friend and I went to a indoor RC dirt track, his GPS took us there as it should, the next time we went we could not remember the route, his GPS kept wanting us to make a U turn in the middle of an intersection a few miles from the track, it said on the screen it was tracking 7 satellites, his unit apparently had a glitch.

its a tool, it works or it don't

[Travis]

I'm no expert on GPS but here's my take on it.

Accuracy has less to do with the receiver and more to do with tolerance programmed into the system. A GPS in a fishing boat only has the ability to put you with-in X metres of the mark.

It is largely a defence based system and the accuracy provided is depended on potential security threats at the time, I understand this does change.

I think any speed reading is based on a grid or coordinate calculation. If for example the grids are 10 foot square, and you travelled across 3 grids, the system doesn't actually know if you've covered 30 feet or 21 feet, depending on what point of the first and last grid you started or stopped. Hence the further you travel, the more actuate the reading and why testing it in your car may give you and accurate reading.

Like I said, no expert and happy to be proven wrong but results I seen in boats sometime have been hard to believe.

Cheers!

[pda75]

Hi

I agree. You need 3 or 4 runs with similar speed in order to be sure

For fun, I used to measure my speed while skiing. Here is one of the result : 622 km/h eg 390 mph !

This happened a day I have pushed my arm to the left, having a beer. The GPS was in my skiing suit.

Regards

Pierre

[martin]

Hi

I agree. You need 3 or 4 runs with similar speed in order to be sure

For fun, I used to measure my speed while skiing. Here is one of the result : 622 km/h eg 390 mph !

This happened a day I have pushed my arm to the left, having a beer. The GPS was in my skiing suit.

Regards

Pierre

I have some friends that im sure can drink a beer that quick. Martin.

[pda75]

I have some friends that im sure can drink a beer that quick. Martin.

Show me the picture of the GPS

[martin]

That going by how much they can drink . Martin.