trajectory length

[OpenPTVuser]

Hello Yosef and Alex,
Thank you for the valuable package you provided.
I am using flowtracks for Lagrangian studies and I have two questions I hope you can help me with those:

1. I get the length of each trajectory by using following line:
   traj.pos()[-1,0]-traj.pos()[0,0]
   the maximum length I get is 0.16 but when I plot traj positions I see the maximum length of the trajectories is equal to the length of the observation volume (0.3 m).
   my guess is that the plot function just join small trajectories and make a longer one or so. If yes, based on what criteria it does that? Please correct me if I am wrong.
   2)is there any class for Lyapunov exponent calculation in flowtracks?
   Thank you for all the help,

[alexlib]

Hi @OpenPTVuser - (it would be nice to know your in person :))

I'm not sure about "1. I see the maximum length" - let's get a small sample here (h5 file) and we'll take a look. Maybe it only looks visually longer. Note that here you refer to the 'x' direction - maybe you see the 'y' direction longer? what does it say: traj.pos()[-1,1] - traj.pos()[0,1]

2. Not yet, I think we'll need to think if it's a common request and maybe add it in the future. If you have some time and make some progress, please share it .

[OpenPTVuser]

Hi,
Sorry for my delayed reply. So I checked and it turns out the length of the trajectory in plot is equal to the calculated one so the problem solved. But I see some of the trajectories start from minus x. I wonder why the start point of each trajectory is not x=0?
Also I noticed I trajectories are seen only on one side of the flow, How do you think I can check the reasons for this?(attached file)
about the finite time Lyapunov exponent, I am trying to apply one the previous works in mechnical engineering. I will let you know any progress.
thanks,
Nikki,

[alexlib]

Hi,
I do not see the attached file, so please share it again.
regarding the negative 'x' - it's absolutely normal and it depends on the coordinate system that was defined by your calibration.
good luck with the Lyapunov exponents.

[OpenPTVuser]

[OpenPTVuser]

Please find the attached. The observation area is 30*30 cm.

[alexlib]

Looks very good. what is the problem, please @OpenPTVuser ?

[OpenPTVuser]

The question is that what could be the possible reasons that I do not get the trajectories on the other side of the flow?
Is the code sensitive to the mean velocity? because the mean velocity of the other side is quiet higher.
Thanks,

[alexlib]

could be, also calibration can be another reason.