Adding sectors programmatically - issues?

[dboyles]

I was autocrossing this weekend and put my DL1 through its virgin runs in my car and in a friend's. I'm doing analysis now, and I can't seem to get run times to make sense relative to the official times at the event.

I can get a pretty accurate "start of run" marker by looking at the longitudinal acceleration of the cars. Actually I'm creating a "staging" marker where the car is at rest before the start line, and then programmatically adding the "start of run" marker 2 meters after that. But when I try to add a "end of run" marker programmatically by doing it xx.xxx seconds after the "start of run" marker (where xx.xxx is the official time for the run), the times are off fairly significantly (~1 second), and not in any identifiable pattern. For example, I have two runs for my friend in his car, but the software is showing a difference of 0.27 seconds between those two runs, where his official times were about 0.7 seconds apart.

A question that may lead me to an answer: when a marker is added programmatically based on time (from a previous marker), on what run is that based?

[Applejack]

I used the same process you described this weekend with mostly good results. I'm getting the times to match to around a tenth of a second.

One thing you might try is to only load one run while you define your markers so you know which one it will base the time on. That's what I do after my first run while trying to look at each run throughout the heat.

The only problem that I see with the time being wrong is that your fastest run (on the region time sheet) isn't always the fastest as you found. This means that the time slip graph won't be based on your fastest run. You can still use those results to help you, but it just takes more thought.

[dboyles]

Thanks for the reply, Jason. I'll give that a shot (defining start/finish/sectors based on one run). However, one issue I've run into seems to be a common one - dealing with GPS drift over time. I'm finding that runs that are only an hour or so apart are several meters off on the start. It's bad enough that two runs with roughly the same path through a slalom look like a double helix, so comparing drivers in different heats is basically impossible.