[WestonP22]

I couldn't resist my curiosity and downloaded G-Tac Pro last night... I've only played with the lap timing on the street in my truck so far, but from what I've seen it's a really simple and easy to use app. The only problem I ran into was getting the iPhone to get a strong GPS signal inside my truck, but it does compensate for that somewhat... the output data indicates the precision level of each GPS sample, and it only writes GPS info when it is able to, so sometimes you see GPS samples that are a few seconds apart, and other times you see 1 or 2 per second. The really good news is that the accelerometer data appears to be sampling at 30Hz, which fairly high.

The app records the data, shows you your Max G's and speed, and plots it all along with the map of where you were. It does not give you much for doing analysis, but I wouldn't expect that from an iPhone app either. The big deal here is that it can export it's raw data. The output data is a raw CSV dump that you e-mail to yourself from the iPhone, and it consists of two separate sections... GPS data and accelerometer data. I am now tempted to put together a simple program that combines the two sections, uses the accelerometer data to interpolate the GPS data (this is what most big name dataloggers do), maybe does some simple analysis, and exports a nice CSV file that can be overlaid onto video using RaceRender, TrackVision, or Dashware. That would make this a much more feasible datalogging solution.

Here is a quick sample of what the data export looks like...

Description:
Date: Mar 22, 2009 12:41 AM
Elapsed Time: N/A
Top Speed (GPS): 26mph
Max Accel. G: 0.33
Max Brake G: -0.34
Max Left G: 0.52
Max Right G: 0.27
Notes:
Enter Notes

========= GPS Data =========
time (sec),Latitude,Longitude,Accuracy (m),Speed (m/s),Course (deg from N)
0.00,39.996253,-105.086782,17,0.000000,90.000000
2.19,39.996243,-105.086696,17,0.000000,90.000000
3.38,39.996232,-105.086610,17,8.025333,94.000000
4.28,39.996221,-105.086524,17,7.510889,94.000000
4.87,39.996221,-105.086460,9,8.951333,92.000000
5.78,39.996221,-105.086331,9,10.906222,90.000000
6.26,39.996221,-105.086288,9,10.288889,90.000000
6.87,39.996221,-105.086160,9,10.649000,90.000000
7.56,39.996221,-105.086074,9,10.186000,90.000000
8.38,39.996210,-105.085967,9,10.803333,90.000000
...

======= End GPS Data =======

==== Accelerometer Data ====
time (sec),RPM,Longitudinal Gs,Lateral Gs
0.00,0,0.000,0.000
0.01,0,0.102,0.000
0.06,0,0.128,-0.002
0.10,0,0.155,-0.001
0.13,0,0.179,-0.001
0.17,0,0.202,-0.001
0.20,0,0.225,0.003
0.23,0,0.246,0.003
0.27,0,0.263,0.005
0.30,0,0.278,0.003
0.33,0,0.292,0.001
0.37,0,0.301,0.008
0.40,0,0.312,0.011
0.44,0,0.318,0.016
0.48,0,0.323,0.017
0.51,0,0.322,0.017
0.55,0,0.326,0.017
0.58,0,0.325,0.016
0.62,0,0.325,0.012
0.65,0,0.324,0.009
0.68,0,0.324,0.008
0.72,0,0.323,0.005
0.76,0,0.325,0.003
0.80,0,0.323,0.002
0.83,0,0.321,-0.000
0.87,0,0.324,-0.002
0.91,0,0.321,0.001
0.94,0,0.315,0.005
0.98,0,0.316,0.010
1.02,0,0.318,0.015
...

== End Accelerometer Data ==