Synchronize data manually at import
Aim
To synchronize the tracking data and the external data if it was not possible to connect the EthoVision XT computer and the external DAQ system.
You can manually synchronize external and tracking data during import of external data into EthoVision XT:
▪Shift the offset. This means that the complete external Data Set is shifted in time. The duration of the external Data Set remains unchanged. Shifting is done by changing the Start Date/Time of a Data Set.
▪Stretch or shrink the external data set. This means that the duration of the external data set is changed to match the duration of an acquired Trial. Stretching the external data set is done by changing the Start Date/Time and/or the Stop Date/Time. This way you can either stretch or shrink the duration of the data set.
Manual synchronization of external data and tracking data is accurate to within one millisecond. However, note that the sample rate of EthoVision XT, and therefore the resolution of the derived data, can never be higher than the video frame rate.
When do I need to Shift the offset?
For example, you started acquisition on your DAQ system 10 seconds after you started acquisition in EthoVision XT. During import, shift your external data set 10 seconds to match the offset of the Trial.
When do I need to Stretch/Shrink?
You need stretching/shrinking in the scenario that you carry out acquisition during a prolonged period of time during which the clocks of the EthoVision XT computer and the DAQ computer start running 'out of sync' (you started with synchronized clocks (see below how to synchronize computer clocks).
example You carry out tracking for 24 hours and after this period you notice that the DAQ computer is 10 seconds ahead of the EthoVision XT computer. This means you need to shrink the external data set by changing the Stop Time of the data set to 10 seconds earlier.
To facilitate manual synchronization
You can facilitate manual synchronization by synchronizing the clock of the EthoVision computer and the computer on which the external DAQ system is running, before acquisition. You can use one of the following methods:
▪If the computers are situated next to each other, double-click the clock in the taskbar at the bottom of the screen on both computers. In the Date & Time tab, set both clocks to the same time.
▪In all cases: use an online clock, when connected to the Internet, to set both clocks to the same time (see description above); or use NetTime, a simple Network Time Protocol (SNTP).
If, for some reason, it is not possible to synchronize the computer clocks there is a more advanced method to facilitate manual synchronization. This method only works when the external data file contains information about date and time of acquisition.
1.Acquire tracking data in EthoVision XT and external data on the DAQ system and make sure on both systems a synchronization event is recorded.
For example, you can use a relay to create a peak on your DAQ system and simultaneously switch on a light which is visible in the video.
2.Import the external data into EthoVision XT.
3.Visualize the data by choosing Analysis > Results > Plot Integrated Data. Go to the position in the video where the swiping action occurs. Note down the time stamp.
4.In the external data window, move the hairline to the position where the peak, caused by the swiping action, occurs. Note down the corresponding time.
example The swiping action in the video occurred at 1.01. The corresponding peak in the external data occurred at 0.85 in the external data plot, so 16 seconds earlier.
5.In the Trial list, remove the external data. To do so, select the columns that contain the external data sets, right-click and select Delete Variable.
6.Change the start time of the external data file by doing one of the following:
▪Open the external data file (for example, with Notepad) and change the start time.
▪Import the external data file. In the Import External Data window, you can change the start time of the external data set (see below).
example The difference in offset was 16 seconds (with the external data starting earlier than the tracking data). This means that the start time of the external data set should be set to 16 seconds later.
7.If you have edited the external data file, re-import it into EthoVision XT.
Manual synchronization of tracking data and external data is accurate to within one millisecond.
1.Import the external data that was simultaneously acquired during live tracking into EthoVision XT.
2.In the Import External Data window, double-click the Start Date/Time cell of the external data set you want to shift.
3.In this cell, click the year, month, day, hours, minutes, seconds or milliseconds and change them by using the arrow-up/arrow-down on your keyboard, the up/down arrow at the right side of the cell or just type in the desired value.
When you change the Start Date/Time of a Data Set, the Stop Date/Time also changes. As a result the duration remains the same.
4.Finish import.
To stretch/shrink an external data set
Stretching or shrinking can be used in the unlikely case that during acquisition the clock of the external DAQ system starts running out of sync with the clock of the EthoVision computer. This probably only occurs when live tracking is performed for a prolonged period of time. For example, in EthoVision XT, the clock time is determined by the camera frame rate. If the camera frame rate is not accurate, for example when a low-end consumer model is used, the time stamps in EthoVision gradually become out of sync with the DAQ computer clock. Then you need to manually increase or decrease the duration of the external data set.
1.Import the external data that was simultaneously acquired during live tracking into EthoVision XT.
Shift the external data set if necessary (see above).
2.To stretch the Import External Data window, double-click the Stop Date/Time cell of the external data set you want to stretch.
3.In this cell, click the year, month, day, hours, minutes, seconds or milliseconds and change them by using the arrow-up on your keyboard or the up-arrow at the right of the cell.
You can shorten the external data set, by changing the Stop Date/Time to earlier.
4.Finish import.