Garmin edge 305

[fandacious]

Also noticed that there is about a 10km diff between the speedometer on my car and that of the GPS. Should make for an interesting argument with the cops.

 

 

all cars speedo's underread

[jacostrydom]

The GPS will be the better indication of the two

[The Saint]

Ja but how exactly would we explain that to our traffic cop friends. Can you imagine just trying to get them to understand that you can get your speed reading from a thingie in the sky.

[NotSoBigBen]

But I would imagine that your 'GPRS' (as my m-i-l calls it but she also says things like M3P and DDV so ....) would be closer to the trefik kops gatsemeeter or whatever laser thing it is these days?

[The Saint]

Not so sure about that Ben. Got a fine the other day with a camera where my speedo was on around 130Km. The fine said 131Km but according to my GPS I was doing 119KM.

[mountain_lion]

 

Afstand met 'n GPS in 'n reguit lyn is baie akkuraat' date=' but the 305 takes a reading of position etc every few seconds and connect the dots mathematically with straight lines. Lots of curves (MTB) would make it more inaccurate. I would think that there is also a discrepency with regards to ascending and descending. I would think that any method to measure distance travelled on a bike that can come to within 5% is pretty dam good enough. (Most car manufacturers will not claim better than 10% - That is why they only trap from 10% over the speed limit)[/quote']

 

Korrek in teorie...

However in practice the difference is not noticeable under normal cycling conditions.

 

For ascending and descending to have an influence on the distance traveled, the slope needs to be very steep, much steeper than is normaly done by bicycle.

 

A 20% slope is steep enough that most people cannot cycle it for more than a very short distance. Go do the math and you will see that even for a 20% slope the 2D & 3D distance does not differ enough to matter.

 

The straight lines between track points only matter at very high speeds, faster than you normally travel by bicycle.

I am not sure what the max sample rate is for the Edge, but it is not less than a track point every 2 seconds.

In the auto mode, it uses a software algorithm to dynamically determine the sample rate. When moving in a straight line the sample rate is low, but when changing direction, the sample rate is high, thus optimizing the available storage memory.

 

I always use my Edge (and other GPS devices) in auto mode and have always found the accuracy to be high, even when traveling by car.

 

GPS devices are much more accurate than any wheel based measuring device.

 

 

[NotSoBigBen]

Not so sure about that Ben. Got a fine the other day with a camera where my speedo was on around 130Km. The fine said 131Km but according to my GPS I was doing 119KM.

 

Like I said 'I would imagine'

 

As you say how to argue that with the powers that be

[The Saint]

Yup that would be one for the Judge. Only thing is I am not so sure how well my explanation of the thingie in the sky would be understood by him either. 

[JasonW]

Yup that would be one for the Judge. Only thing is I am not so sure how well my explanation of the thingie in the sky would be understood by him either. 

 

You could call Mountain Lion as an expert witness

[mountain_lion]

Mux, was this a fixed speed camera or a mobile speed trap?

 

If mobile, it should have been maned and the officer manning it should be able to produce the calibration certificate for the device as well as proof that he has been trained to use said device. Worth stopping at these if you suspect that you have been fined and checking these.

 

For fixed installations, you can also ask for the calibration certificate if you want.

I guess that often these devices are not properly calibrated.

 

Your GPS should be more accurate, but I agree that using a GPS in court might not be easy...

 

 

 

[The Saint]

It was a mobile camera on the N3 placed in the dip just before Mulborro Rd Offramp....but ja the fine was 100 bucks so it probably is just better to pay it rather than risk having a stroke whilst trying to explain that the thingie in the sky is far better at calibrating speed than our Civil Servants who take half an hour to write down your ID Number. 

[Frosty]

Last time I checked, the only time you can question the validity of the calibration certificate is if your speed is less than 105% of the speed limit (i.e. <126 in a 120 zone, or <84 in a 80 zone, etc.).

 

 

 

 

[casspir]

I have had two experiences regarding the use of my own GPS data as opposed to an alleged traffic violation.  In both cases I responded in writing informing the relevant authorities that I do have an accurate GPS log of my travels and that my data differs from their information. 

Check the date and time of the alleged violation in respect of the place.  Sometimes their clocks are way out.  The traffic authorities tend to be quite vague as to the specific place of alleged violation.  This can be confirmed by your GPS data that you can see on software such as Mapsource. 

In both cases the relevant authorities withdrew their cases.  I don't know how long before this won't be possible anymore, but I will keep trying. 

I am not in favour of irresponsible driving etc, rather in favour of accurate reporting and accurate alleged violations. 

Regards,

casspir

 

[Jaco Steyn]

For more information regarding the accuracy of a GPS device such as the Edge 305, go to this forum for more information. It is on the Garmap website. http://www.garmap.co.za/Forum/forum_posts.asp?TID=2128&PN=1

steynja2008-04-23 11:32:42

[mountain_lion]

These 2 PDF documents from  http://www.speedtraps.co.za/info-page.php

might be of interest:

Guidelines_regarding_speed_measurement.pdf

Guidelines_regarding_laser_speed_measurement.pdf