Thread: GPS unit

Hi,
I would imagine that the hand held models would not suit your purpose with the speed display being so small.
I have both, and the Navigator Garmin Nuvi has a large speedo display screen just one click away from the main navigation display.
My son has an iphone that he can use as a head-up display. It shows a mirror image of the numerals that can be viewed in the reflective windscreen.
The LR may not have enough shelf space, nor windscreen curve for this to be usable though.
cheers

Thanks, I will check out the Navigator.
I can't see the sense in an I Fone at $60 bucks a month for a glorified speedo....
I could have another couple of series vehicles registered for that sort of gold.


Thanks again,
Mick

Originally Posted by mick88

<snip>The main reason I want it is for an accurate speedo</snip>

I think we put too much credence in a speed reading from a GPS.

I've got an iPad and an iPhone with an enhanced GPS receiver. Running the same software (Memory-Map on both or TomTom on both) they give different speed readings by several Km/h. This is on a straight road without tree cover with me trying to keep the speed as stable as possible. It's not consistent either - sometimes the iPad will read higher and at other times the iPhone will read higher. Sometimes I can get a (low) speed reading whilst parked. All I can put it down to in tolerances and inaccuracies inherent in satellite readings.

Whilst driving on winding roads the problem is worse as the GPS approximates the distance traveled with a series of straight lines (between readings).

Personally, my view is that a calibrated speedo is the most accurate measurement available.

Originally Posted by RVR110

I think we put too much credence in a speed reading from a GPS.

I've got an iPad and an iPhone with an enhanced GPS receiver. Running the same software (Memory-Map on both or TomTom on both) they give different speed readings by several Km/h. This is on a straight road without tree cover with me trying to keep the speed as stable as possible. It's not consistent either - sometimes the iPad will read higher and at other times the iPhone will read higher. Sometimes I can get a (low) speed reading whilst parked. All I can put it down to in tolerances and inaccuracies inherent in satellite readings.

Whilst driving on winding roads the problem is worse as the GPS approximates the distance traveled with a series of straight lines (between readings).

Personally, my view is that a calibrated speedo is the most accurate measurement available.

I find that the GPS speed from my Chinese GPS is accurate to the nearest 1kph at least 99% of the time, and just as accurate as a my speedo. Even on hills I find the GPS reads the same as my speedo (if you take into account the error caused by larger than standard tyres).
Perhaps there is a bit more interference in Sydney, or your signal strength is not good.

Mick,
A cheap $60 GPS from china plonked on your windscreen will do the job, you are after.

Originally Posted by biggin

Perhaps there is a bit more interference in Sydney, or your signal strength is not good.

It was "on a straight road without tree cover". It wasn't anywhere near Sydney or any other major city. But that's inconsequential - the overall point of what I was saying obviously wasn't adequately made. Oh well.

Originally Posted by RVR110

I think we put too much credence in a speed reading from a GPS.

I've got an iPad and an iPhone with an enhanced GPS receiver. Running the same software (Memory-Map on both or TomTom on both) they give different speed readings by several Km/h. This is on a straight road without tree cover with me trying to keep the speed as stable as possible. It's not consistent either - sometimes the iPad will read higher and at other times the iPhone will read higher. Sometimes I can get a (low) speed reading whilst parked. All I can put it down to in tolerances and inaccuracies inherent in satellite readings.

Whilst driving on winding roads the problem is worse as the GPS approximates the distance traveled with a series of straight lines (between readings).

Personally, my view is that a calibrated speedo is the most accurate measurement available.

Might be more to do with the app you are using.

Most receivers compute speed by a combination of movement per unit time and computing the doppler shift in the pseudo range signals from the satellites. The speed is smoothed and not instantaneous speed............................................. .................................Velocity measured by a GPS is inherently 3 dimension, but consumer GPS receivers only report 2D (horizontal) speed on their readout. Garmin's specifications quote 0.1mph accuracy but due to signal degredation problems noted above, perhaps 0.5mph accuracy in typical automobile applications would be what you can count on.

A speed when you are parked can be due to a number of things, poor satellite geometry, multipath signals, obstructed view etc. Ipads etc also use assisted GPS where cell data or wifi is used in conjunction with the GPS to speed up acquisition (don't know what effect that may have)

Originally Posted by Bushie

A speed when you are parked can be due to a number of things, poor satellite geometry, multipath signals, obstructed view etc.

I agree as this is exactly the point. Just because a device has a digital readout and is based on satellite telemetry does not make it "accurate". Every form of measurement has its inherent measurement uncertainty (aka error or inexactness).