Topic: Trajectory calculation kinovea 0.8.24

Following a trajectory in kinovea 0.8.24 does not work. In version 0.8.15 its done marking the cross and after digitizing position right button "Follow trajectory". Then 2 boxes for semiautomatic digitization appear. In this version the option "Follow trajectory" exists but the program do not follow it.
This also affects to the velocity calculus.

Re: Trajectory calculation kinovea 0.8.24

Hi,
In recent versions there are two different concepts for tracking.
Trajectory tracking is done by directly right clicking the video. This corresponds to the behavior in previous versions. Kinematics are only available in this mode.

There is also drawing tracking, where the points comprising the drawing (marker, line, angle, etc.) are tracked independently. This is done by right clicking the drawing. If you first add a marker and then right click it and "follow trajectory" you will be in this mode.
With this type of tracking the boxes are not visible. The marker should be attached to the imaged object though and if you move the playhead it should follow whatever is beneath it.

Please give more details as to which tracking type does not work.

Re: Trajectory calculation kinovea 0.8.24

Thanks,

I've tried what you say, and works smile
The only thing is that when you ask to show measure it shows position and displacement values, but for velocity, acceleration and their components it appear ### instead of numbers.

Another thing, that in my opinion could be improved is the icon that appear when clicking the hand function and you want to move an extreme of a line. The white hand that moves during left button mouse clicked do not allow position the line on to the articular centre, it diminish digitizing precision. A cross or a transparent hand would be better.

Thank you

Re: Trajectory calculation kinovea 0.8.24

coxisambo wrote:

The only thing is that when you ask to show measure it shows position and displacement values, but for velocity, acceleration and their components it appear ### instead of numbers.

This usually happens when there aren't enough data points to compute the value. Since velocity and acceleration are derivatives and the data is filtered to remove noise, there is a minimum number of points that needs to be present before and after the position of interest in order to calculate the kinematic quantity at that point.

coxisambo wrote:

The white hand that moves during left button mouse clicked do not allow position the line on to the articular centre, it diminish digitizing precision. A cross or a transparent hand would be better.

Yes, fair point. Note that you can zoom in 600% with CTRL+mouse scroll, which should provide sub-pixel accuracy.

Re: Trajectory calculation kinovea 0.8.24

Then how many points are needed to be digitized?
With the version 0.8.15 you could calculate velocity between two contiguous frames (to achieve "instant" velocity).
I've tried to digitize a full trajectory with 10 frames or more with a conventional camera (25Hz) and a high speed velocity camera (300Hz) and ### appear in both cases.
With the 300Hz cam, when you go back frame by frame appear also a velocity number, always 0 but with pixel/s units, and the video is already calibrated.

Re: Trajectory calculation kinovea 0.8.24

Ok, that is strange and sounds like a bug. You should be able to see velocity as soon as a trajectory point has two neighbors, before and after, and acceleration as soon as it has four neighbors. So only the first and last points should be "###".

What happens when you display "Position" instead? Do you get anything?
Can you save to a KVA file and send it by mail please? (joan at kinovea dot org), thanks.
Can you right click the trajectory and go into "Data analysis" dialog. Do you get the position over time and other plots there?

Re: Trajectory calculation kinovea 0.8.24

I've been working with the version 0.8.24 the way you told me to calculate trajectories and its fine. the ### appears in the last photogram digitized. I was wrong
Thank you