Motive assigning incorrect time stamps to data

[msb]

Hello,

I am using Motive 1.7.5 on a 64bit system. I have 3 Flex13 cameras and the OptiHub 2.

I want to externally trigger the OptiTrack cameras, and to do this I have an external signal generator which generates pulses of 3V at frequencies between 20 and 40 Hz. I connect the signal generator to the External Sync In on the OptiHub, set the Synchronisation within Motive to "Custom Synchronisation", the Source to "Sync in", and the Input Trigger to "Rising Edge". If I change the frequency of my signal generator I can see the FPS of the camera changing accordingly, as expected, also while recording.

Now, here are a number of strange behaviours, which all seem to be connected:
1) Using my signal generator at either 20 or 40 Hz, when I start recording, the increasing time in the Timeline pane is clearly not in real time - the "seconds" tick by much slower than a real second, and the "seconds" are different lengths for different frequencies (lower freq = longer seconds). If I switch to a "Free run" in the Synchronisation pane (i.e. not using the external trigger) the "seconds" are correct again. (note that I have also noticed that the milliseconds never seem to get to 1000, they only reach something just over 100, whether I am using the external trigger or not.)

2) If I export the tracking data then the time stamps seem to be correct: the final time is what I expect, as is the time between the stamps. The final time stamp is different to what I observe in the Timeline in Motive.

3) I am interested in changing the frequency of the motion tracking during a take. To test this I start a take using the external trigger with a frequency of 20Hz, after 5 seconds (real seconds measured by another clock) I change the frequency to 40 Hz, and after another 5 seconds (real seconds) I stop the take. Firstly, I can clearly see that the speed of the "seconds" in the Timeline speed up after I change the frequency. Secondly, I analyse the exported .csv file and find that the time stamps are all equally spaced throughout the data with 50ms between them (I had expected the first 5 seconds of data to have a period of 50ms and the second 5 seconds to have a period of 25ms). I can also see that the last time stamp is around 15 seconds (instead of 10 seconds, which is how long I recorded for).

4) I observe similar behaviour if I do not use the external trigger, and I manually change the camera FPS during the take. The displayed "seconds" in the Timeline are always 1 second long (which is a different behaviour to point (3) above), but the time stamps in the exported csv file are all the same, which is not correct.

This is very unfortunate behaviour. I had expected that the recorded time stamps are in real time, but they seem to be set according to the frequency at the beginning of the take.

Is this a bug, or a feature? Is it possible to tell Motive to use the real time relative to the start of the take, for each measurement, in the exported data file?

Many thanks!

[steven.andrews]

Hello msb,

Thank you for reaching out to us regarding your questions, and for providing such a detailed explanation of your testing and your issues.


I am not sure why the displayed time is not correct when you are providing a synchronization pulse for the cameras. A couple of issues have been fixed related to synchronization since 1.7.5, and it is possible that this was one of them. If you have access to newer versions of Motive, I would recommend you upgrade to the current Motive 1.9 Final for a number of reasons.

If you could select your Take in the Project Pane, and observe the reported duration and frequency in its properties at the bottom of the pane, you should check to see if these match the actual duration and frequency. In some instances, this version of Motive was not recording the information correctly, which would affect the data that is exported from Motive.


I can confirm that Motive does not record changes to the frame rate in realtime. This is a very uncommon workflow, and the frame rate is expected to be constant for the duration of a Take.


I hope this information helps with your troubleshooting. If there is anything else we can do to assist you, please feel free to open a support ticket with us at help.naturalpoint.com

Best,
--
Steven Andrews
OptiTrack | Customer Support Engineer

[msb]

Thank you for your prompt response.

I submitted a reply yesterday but for some reason it has not been posted.

I can confirm that for Motive 1.7.5 the take properties in the Properties pane are not being displayed correctly. The "Time Duration" is incorrect, but the "Frame rate" and "Total Frames" are correct. If I calculate (Total Frames)/(Frame rate) I get the expected (correct) time duration of the take.

I will be upgrading to 1.9.0 in the next few days and I will check whether this issue has been solved.