Performance meter GPS software?

**96TransAm** · 09-19-2006, 02:42 PM

Is there any GPS software that can give you performance estimates? Like 0-60 time, 1/4th time, estimated horsepower from mile per hour in 1/4th of a mile (i.e. 115 miles an hour in 1/4th of a mile would be around 450hp at 3800lb race weight)

There are lots of non GPS units that due this, but they all have their flaws due to tire spin, and atmosphere conditions. So GPS would be perfect.

**evandude** · 09-19-2006, 02:57 PM

I'm not personally aware of any; but then again I've never looked. but the idea raises some issues such as update rate, and position accuracy. IIRC, GPS receivers for the PC only update once a second, and position accuracy seems to be on the order of several meters. Considering the amount of money some people spend to shave tenths of a second from their 1/4 mile time, an accuracy of only around 1 second doesn't seem real great.

**96TransAm** · 09-19-2006, 03:23 PM

Originally Posted by evandude

I'm not personally aware of any; but then again I've never looked. but the idea raises some issues such as update rate, and position accuracy. IIRC, GPS receivers for the PC only update once a second, and position accuracy seems to be on the order of several meters. Considering the amount of money some people spend to shave tenths of a second from their 1/4 mile time, an accuracy of only around 1 second doesn't seem real great.

That would be an issue. I guess that is why the GPS standalone units that do this cost thousands.

**v8 scimitar** · 09-19-2006, 03:56 PM

The stuff you are on about has a lot more than GPS in them, in fact they probably use GPS very little and use it more as a sales pitch than anything else. The main part is the accelerometer. If you know the weight, G pulled and the length of time along with engine RPM and a few other things you can work out just about anything. So far as I know GPS is GPS whether its domestic or military that's why smart weapons have a + or - 5 meter accuracy.

**96TransAm** · 09-19-2006, 04:04 PM

Originally Posted by v8 scimitar

The stuff you are on about has a lot more than GPS in them, in fact they probably use GPS very little and use it more as a sales pitch than anything else. The main part is the accelerometer. If you know the weight, G pulled and the length of time along with engine RPM and a few other things you can work out just about anything. So far as I know GPS is GPS whether its domestic or military that's why smart weapons have a + or - 5 meter accuracy.

The unit I'm tailing about is not a accelerometer, it has just a GPS unit that size of a tool box. A accelerometer would need to be set up a level surface and would have sensors, this thing was just a box with an antenna.

I read about it when car and driver did a test on a bunch of accelerometer performance meters against their GPS based unit.

Our sophisticated VBOX system doesn’t use accelerometers, precisely to avoid this problem. Instead, the VBOX relies on the global-positioning system (GPS) to measure a vehicle’s motion. To work, the VBOX must be in communication with at least four of 24 GPS satellites orbiting the earth. As a vehicle travels down the test venue, there’s a minuscule shift in the arrival time of the radio signals that travel between the satellites and the VBOX’s antenna. By measuring this shift, the VBOX calculates speed, acceleration, and distance. Racelogic, the company that makes the VBOX, asserts that its devices are accurate to within 0.06 mph.

They said it cost 30 grand..
http://www.caranddriver.com/features...ters-work.html

So it seems it compensates for the delay by using a mathematical algorithm of some sort. So, who do you need a 30 thousand dollar unit to do this? I would think software could do it just as well.

**wi77iam** · 09-20-2006, 06:46 PM

Originally Posted by v8 scimitar

So far as I know GPS is GPS whether its domestic or military that's why smart weapons have a + or - 5 meter accuracy.

Differential GPS and WAAS greatly increase the accuracy - probably down to a couple meters. Military GPS using L1 and L2 encrypted signals has accuracy much less than +/- 5 feet. How do you think they put those smart bombs through a particular window or down a ventilation shaft?

**god_of_cpu** · 09-20-2006, 07:20 PM

Originally Posted by 96TransAm

The unit I'm tailing about is not a accelerometer, it has just a GPS unit that size of a tool box. A accelerometer would need to be set up a level surface and would have sensors, this thing was just a box with an antenna.

I read about it when car and driver did a test on a bunch of accelerometer performance meters against their GPS based unit.

They said it cost 30 grand..
http://www.caranddriver.com/features...ters-work.html

So it seems it compensates for the delay by using a mathematical algorithm of some sort. So, who do you need a 30 thousand dollar unit to do this? I would think software could do it just as well.

It's not really a software issue. They must be using special hardware. A typical USB based GPS has an update rate of no more then 5 Hz, 1 Hz is probably typical. If you spend enough money, you can get special hardware that update alot faster like 30-50 Hz which is probably what they are using and why it costs 30 grand.

**96TransAm** · 09-21-2006, 09:08 AM

Interesting...So think we can start a GP on some?

**evandude** · 09-21-2006, 09:36 AM

In what little I've read about it, it seems one of the big limitations to accuracy and speed is the amount of number-crunching required. The GPS unit triangulates its position in 3 dimensions by doing a bunch of high-precision floating-point math on the signal strengths and directions from all the satellites.

an example of the amount of number-crunching power it takes:
http://www.dsprelated.com/showmessage/22833/1.php

The theoretical limit is down to the integration time for the receiver,
typically 1-10ms. If you want high dynamics, you need to update faster.
For car racing, it's probably closer to 1ms.

Most comercial receivers output 1 position per second because it takes
some number crunching to compute the satellite positions and solve for
the receiver position. This is purely a matter of computing power.

Given a fast enough processor, 1000 positions per second is possible.
I was running an automotive receiver IC (60MHz,32bit MIPS processor)
at about 10 fixes per second, getting close to 100% CPU.

based on a quick googling, it looks like a DSP chip of that speed is something like $25 in production quantities, and I would imagine a GPS system that used it would be a few hundred bucks at least, and for something in the range of 30-50Hz (3-5 times faster) I'd expect the price to rise exponentially, which seems to be the case based on the prices that have been tossed around.

**96TransAm** · 09-21-2006, 09:40 AM

Well then, a modern high end CPU would be able to do it easy you would think. The unit that cost them 30 grand is about 5 years old now, CPUs have come a long way.