Speedo Correction Is it possible

[phonebooth]

I might be a little lost here but why do people treat GPS speed as reliable for day to day driving? I can understand smashing it down a straight road, that would be pretty accurate. In normal driving conditions with the GPS having to plot your position and measure the time over distance to calculate your speed, I don't see how that can be accurate. In indicative figure, yeah. You'd be varying your speed for traffic, corners etc. Surely the GPS can't output an accurate figure if you're doing that.

Then again, I'm no GPS expert!

[Guest001]

I might be a little lost here but why do people treat GPS speed as reliable for day to day driving? I can understand smashing it down a straight road, that would be pretty accurate. In normal driving conditions with the GPS having to plot your position and measure the time over distance to calculate your speed, I don't see how that can be accurate. In indicative figure, yeah. You'd be varying your speed for traffic, corners etc. Surely the GPS can't output an accurate figure if you're doing that.

Then again, I'm no GPS expert!

Read this then and learn LOL

To calculate the Longitude, Latitude and Height position, a GPS receiver precisely measures the different speed of light (299,792 km/s) delays in the signals coming from 4 or more satellites. The distance to each satellite is calculated, and then using trilateration, the 3D position of the GPS antenna is calculated.


How GPS Receivers Work | HowStuffWorks

As far as how often it does it, its almost instant so as you slow your car so does the reading Its not like it updates ever 30 secs or something

[Guest001]

Have been looking through the modules in my OBDII and in the ECU I notice there is a long coding one called WHEEL CIRC.

I wonder if altering that will fool it into doing less impulses per KM.

I havent connected to the car to see what happens if I open it up

[Ozsko]

Read this then and learn LOL

To calculate the Longitude, Latitude and Height position, a GPS receiver precisely measures the different speed of light (299,792 km/s) delays in the signals coming from 4 or more satellites. The distance to each satellite is calculated, and then using trilateration, the 3D position of the GPS antenna is calculated.


How GPS Receivers Work | HowStuffWorks

As far as how often it does it, its almost instant so as you slow your car so does the reading Its not like it updates ever 30 secs or something

It is quite common in the southern parts of Oz not to lock onto four satellites, we encountered this many times when data logging race cars and the Tiguan never tells you how many satellites it has access to where we could see it against the data. GPS signals available to non military users works to a tolerance which varies when it gets manipulated by the US authorities so when that happens the accuracy wanders around. We used physical sensors and overlaid the data with GPS and the GPS ALWAYS lagged in both speed and other readings without fail. I have connections with a family company which designs and builds this stuff and believe me it ain't fool proof until you get into the military grade GPS which they do.

[phonebooth]

To answer your question, "Is it possible?" Probably. Should you do it? Probably not.

[dgp]

I think if it’s possible, hillbilly should go for it. Why not make the speedo as accurate as possible?
I will be interested if it can be done.

[Guest001]

It is quite common in the southern parts of Oz not to lock onto four satellites, we encountered this many times when data logging race cars and the Tiguan never tells you how many satellites it has access to where we could see it against the data. GPS signals available to non military users works to a tolerance which varies when it gets manipulated by the US authorities so when that happens the accuracy wanders around. We used physical sensors and overlaid the data with GPS and the GPS ALWAYS lagged in both speed and other readings without fail. I have connections with a family company which designs and builds this stuff and believe me it ain't fool proof until you get into the military grade GPS which they do.

Yeah well my wifes BF's son did most of the design work on the original Navmans in NZ . Sadly i wouldnt recommend one of them.

However they are accurate to a much closer distance than before the US military had them fudged up years ago and then they allowed it to be more accurate.. My Tomtom usually gets more than 4 (Most times) lol

[Ozsko]

Yeah well my wifes BF's son

A galaxy of relationships I don't want to even think about, is that like the bloke I know who's sons wife's brother can get me a deal on a car?. The US regularly changes the accuracy and you can see the GPS changing in a full day of data as it happens due to normal drift during the day. GPS is not the accurate thing that we all think it is, not by a long shot.

[Guest001]

, is that like the bloke I know who's sons wife's brother can get me a deal on a car?. .

No true story He did the original Navman and his wife who was also an engineer was one of the ones who developed the F& P dishdrawer

Quite a talented pair

I dont think we need to worry about all the nuances when just checking our cars speed really.

However I still would like to get mine a bit closer

[theresanothersteve]

Read this then and learn LOL

To calculate the Longitude, Latitude and Height position, a GPS receiver precisely measures the different speed of light (299,792 km/s) delays in the signals coming from 4 or more satellites. The distance to each satellite is calculated, and then using trilateration, the 3D position of the GPS antenna is calculated.


How GPS Receivers Work | HowStuffWorks

As far as how often it does it, its almost instant so as you slow your car so does the reading Its not like it updates ever 30 secs or something

The missing piece of the puzzle is bread crumbing. The GPS records your location as a 3d reference. Then it records the next. The distance between the points is calculated, along with the time elapsed between each point. This means when you are accelerating or decelerating the speed lags slightly behind the true speed.

At a constant, or near constant, speed the indicated speed is more reliable than that the speedo shows.