2 seconds OBD data delay in video

[Falc09]

Thank you for your help!

I attached the exported .csv file and additionally created an Excel file with "Text in Spalten" option. I am not sure where and what to look for so I need a little more input.

[gplracerx]

You're not going to fix your problem by changing delays. The problem is that the data aren't very good. The delays are actually about right. It's hard to tell whether it's the GPS or the OBDII data. I'm betting it's both. The yaw calibration on the accelerometer was way off. I'll have to fix that before I can compare accelerometer data to the GPS and OBDII data.

That's something you can fix using the g-g chart, by the way. There are little icons you can touch to rotate the g-g plot. The plot should look something like a half circle with the flat top parallel to the lateral acceleration axis. I'll show you a before and after when I'm finished.

[gplracerx]

G-G plot before and after rotation of 22 degrees. Notice how you can see straight line braking and acceleration clustered along the lineal axis in the rotated data.



Speed vs time plot, GPS and OBDII. The GPS speed is suspect, in my opinion, because there are places where the speed isn't changing as much as it ought to.



Lineal acceleration vs time plot. Accelerometer (corrected), calculated from GPS and calculated from OBDII. The OBDII calculated acceleration agrees fairly well with the corrected accelerometer data. The GPS, not so much.



Here's the spreadsheet I used to generate the plots:https://dl.dropboxusercontent.com/u/915 ... alc09.xlsx

Try an overlay using OBDII speed instead of GPS speed.

This is also why you might consider the purchase of a higher data rate GPS accessory if you're serious. I like the XGPS160. Higher GPS rate, in my experience, will make the OBDII data look better too.

[Falc09]

Again, thank you for your help! Now I am a little bit more aware of the underlying issues.

So it all comes down to one thing: purchasing high quality hardware first, in my case: at least the recomended GPS and OBD devices.

On the other hand I am not trying to become a racedriver. It's all about having some fun due to luckily living and working less than one hour away from a track that offers regular track days for petrol heads like me

Assuming I try to keep things simple and proceed with the onboard GPS of the S4 and my old and cheap OBD Stick:

Is it possible to use the delay option in laptimer to fix the horizontal 1 second distance between the red and blue line in your speed over time chart? In other words: move the red line one second to the right ... 'delay it by one second'?

That's my last question ... for sure!

[gplracerx]

It's worth a try. I think that might put the OBD data closer to the accelerometer timing as well, the green and blue lines in the last chart.

The GPS fix data, the course map, doesn't look too bad for the lap I looked at. It may just be a problem with how the device calculates speed. I can calculate speed and heading directly from the fix data to see how that goes.

[gplracerx]

I've updated the speed chart with a plot of speed calculated directly from GPS fix data. Sometimes it agrees better with the GPS speed and sometimes better with the OBD speed. If you don't want to spend any more money, you're going to have to live with the ambiguity.