Harry's GPS Suite Forum

This clearly shows there is OBD data. Really curious. Prerequisites are just LapTimer Petrolhead or GrandPrix, the OBD overlay setting set to Standard or Extended, and the availability of OBD data in your lap's recording. The only remaining thing I can offer is you send me an export of one single lap you can reproduce the problem for and send it to me. Use .HLPTRL as format and Harry@gps-laptimer.de as e-mail address. Please send a Contact mail (gray button in LapTimer's startup screen) in addition, so I can try to reproduce this with exactly your settings.

- Harry

I may have found the culprit for this issue. I tried creating a single lap video with data overlay and it worked fine, if I ignore data synchronization issues. Then I attempted to recreate the original video of four consecutive laps, and the data overlay was gone again. Upon close inspection of data for all four laps - what I found is that all data, including OBD, is present for three out of those four laps, and it is missing for the fourth one. I suspect this is the reason why no OBD data is shown when four laps are exported into a single video - one missing piece prevents all four from being exported properly. It is also a mystery why the OBD data is missing for that one lap only (which happened to be the last lap of the day) - it is present for all prior laps and for the next one, which is the first lap of the first session the day after.
I will send you the info for all consecutive four laps.

Speaking about data synchronization issues - I already mentioned in my forum post that I am seeing significant (3-4 seconds) delay between the reality recorded by the external camera and the data displayed on my iPhone screen while driving and capturing the data. Everything on the screen of the Laptimer is happening with the delay, and I am observing similar delays in my data which makes it difficult to synchronize various pieces - timing is way off compared to actual GPS / on track position, OBD pedal inputs are off compared to acceleration sensor data and actual up/downshifts/engine soud in the video, etc. If I manually move the start/end points of the video to synchronize timing with the recorded Laptimer screen display, everything else is off, sometimes beyond the available adjustment range for timing of OBD / acceleration data. Any suggestions?

Thanks for providing the data and analysis.

I had a look into the overlaying code to check OBD handling. In fact, if any of the laps overlaid misses OBD (or TPMS) channels, the full session is done without that overlay.
Actually I thought it is the other way around (one lap with OBD ‣ full session gets overlay). For the OBD selection the test is in fact that if any lap has OBD, selection between None, Standard, Extended is enabled. I will unify this ahead of the v24 release, currently it is inconsistent and misleading.

When synchronizing data and video there are actually two steps:
#1 during recording, LapTimer will fuse incoming data from GPS, IMU, OBD, TPMS; as only GPS is coming in with a timestamp of the measurement, LapTimer needs to make assumptions on how "old" incoming data is. This assumptions are the so called sensor delays. As a sample, IMU / acceleration will have a very small delay between an event in reality and the time is arrives for processing while OBD can be quite late due to low update rates and processing / bandwidth effects. It is important to understand that this synchronization is done during recording. Once fused, it cannot be changed by changing the delay parameters. So if IMU and OBD are off, the next chance is the next track day. The good this is that this part is almost always fine or hard to recognize. Usually one will get the best experience when OBD and video are in sync (rpm / sound is crucial).
#2 during overlay, LapTimer fused video and the pre-synced data; again, LapTimer needs to make an assumption about the delay between a real world event and the time its video frame arrives. This delay can be adjusted in Expert Settings too. The good this is, that this delay is applied during overlaying (Export or Play). Furthermore, the delay can be adjusted on a by lap level using the Sync Dialog.

This is to allow you to fix the problem step by step. In case you find the current IMU/OBD sync not acceptable, you will need to do some test runs with changed sensor delays. Once you make your peace with data level, you can adjust the video sync.

By the way - there can be another sync problem not mentioned so far - in particular when using external footage. Especially video conversion can lead to slightly wrong time stamps due to rounding effects. This will make the video faster or slower than reality. LapTimer will always be off here after a while.

- Harry

Thank you Harry, really appreciate your time working on and clarifying this issue!
With regard to video overlays - not sure why it has to be all or nothing choice. If video export mode simply used the available data to produce an overlay (and drop it for a particular lap if/when data isn't there) the result in this case would have been self explanatory. Similar to how the data parts are cut in and out in the beginning Intro / Extro parts, they can be cut in and out on a "per lap" basis. If I got a video combining four laps, and three of them had OBD data present while the fourth one didn't - it would've probably given me an immediate hint to check that particular lap data and recognize that my OBD sensor had likely lost its Bluetooth connection (I suspect this is what happened on that lap).

Regarding synchronization of different data channels - I think the whole Laptimer community (and those of us in particular who attempt to use Laptimer as a learning tool) would benefit from a dedicated post that explains the "best practices" of getting the data from multiple sources synchronized - not just for the video output (which is nice and a good learning tool for post-track review) but also for making the data charts more accurate and trustworthy. One absolute benefit of using Laptimer data acquisition tools is the ability to review the charts right after the driving session is over - all the useful bits and pieces of information are right there on your smartphone (literally at your fingertips), without the need and demand for extra time to download and review the data on a PC, as other more expensive tools such as AIM require. The data can be easily analyzed to determine what & how things may need to be adjusted for the next session. This would be an extremely useful learning tool - the lack of sync between different channels makes it less useful. How can I learn what to adjust if e.g. my speed chart and throttle application / RPM charts for a particular corner tell two different stories?

So, to sum it up - I am a very dedicated user of the app and very much admire your efforts and the progress in its development! I am not giving up on Harry's Laptimer anytime soon, but I definitely see the need and opportunities for improvements, to make it a stellar data acquisition and learning tool.