Hi All,
There seems to be a lot of reliance on having the data cleaned before showing it. I understand that, but in my day job (making geological models) I tend to make the model I use "fit for purpose", meaning they serve one purpose. When the model is used for something outside the scope I designed it for, things can go wrong.
The mark that I posted a chart of earlier was not the main line mark I had planned to digitise, so I did a rough digitising effort with the aim of showing the data at a much broader scale, where small deviations are not shown as violent deviations in line speed. By posting at a scale that was not envisaged during digitising, people seem to have read more into the chart than they should have. Please look at the scales on a chart of velocity before jumping to conclusions about the data: a jump from 5.5 to 5.7 m/s looks huge when the scale has been enhanced. In reality, it's just noise.
To see what that actually means in Tracker, I've cleaned the data capture more carefully here, paying careful attention to both the chart and the line mark when I position the mark in tracker:
If I happen to miss the optimal position by
a single pixel, this is the result in the chart when the scale is fine. Zoom into the pic and see where the red mark is on the fly line and look at the affect that has on the chart near 3.3 seconds:
In addition to that, there is a LOT of chatter in the video from the iPhone's capture. Sometimes I can fix it, sometimes I can't. You can see where I've had to skip placing marks in Tracker due to that chatter. This video is okay in some parts of the cast, but there are certain parts where frames are all over the place.
I realise these charts are not ideal. At least we can start to measure physical objects in motion without spending tens of thousands of dollars on the hobby.
Cheers,
Graeme
(BTW, I'm still cleaning this data ...)