OptiTrack FLEX:V100R2

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Fontys has an Optitrack motion tracking system with two sets of 6 cameras each. We have a license for Optitrack Arena version 1.7. Both sets of cameras can be used at the same time. Naturalpoint, the creators of the Optitrack system, have excellent tutorial videos available at [1]. Optitrack.png

Where the tracking system can be used

Due to the way the optical tracking system is built, it can’t be used everywhere. The cameras use infrared light and the reflection of this light on reflective markers to detect the position of these markers. This means that the system can’t be used outside, and that fluorescent light bulbs or tubes need to be used for lighting. An Optitrack system is very sensitive, and reflective or bright surfaces within the capturing room should be avoided at all costs. If these surfaces don’t move, they can be masked through software (at the cost of some precision of the entire system). If these surfaces move, though, it won’t be possible to mask them, and they will interfere with the precision of the system. This may cause glitches to occur.

Connecting the cameras

Every camera has a USB port and a sync port. Connect every camera to the USB hub via a USB cable. Note that the PC may not boot if a lot of cameras are connected to it via USB. You may need to disconnect the USB hubs from the PC before attempting to start it up.

Connect.png HUB.png

In order for the Optitrack system to work correctly, the cameras need to be synchronized. The synchronizing is achieved by placing all cameras in a chain using special synchronizing cables. The system has one master camera at the beginning of the sync-chain and a number of slave cameras (usually 5 or 11). The chain starts by connecting the OUT connector of one camera(Master) to the IN connector of another (the Slave camera). The next step is to connect that slave camera’s OUT connector to the next slave’s IN connector. Repeat this process until all cameras are connected. Do NOT connect the last slave OUT connector back to the Master camera’s IN connector. The sync chain is a chain, not a loop!


For more information, see the Optitrack tutorial video “Camera Connections” which can be found at [2]


When the cameras have been successfully connected to the PC, it is time to calibrate the system. To do this, start the Arena Software, click on -> Wizards -> Calibration... Click on Next and deselect the cameras that you don’t want to use. Click Next, then look at the cameras. Each camera will have a number being displayed on the LED display. Make sure that one camera has a ‘1’ displayed, and that all other cameras have different numbers displayed on the LED displays. The first camera in the sync chain will have a ‘1’ displayed, the second one will have a ‘2’ displayed, etc. In a properly working system, no camera will have a ‘0’ displayed. See the troubleshooting section if something seems wrong. Follow the instructions as displayed on the screen, or watch the “Blocking Bad Segments”, “Wanding & Solving” and “Setting the Ground Plane” tutorial videos at [3]

Tracking suit

To track a human body, we need to place markers on a human body. We have a suit which can be used to stick markers on. The Arena software has a skeleton wizard that will help you to set up the markers on the suit correctly. There are several different skeletons you can choose from. For the highest precision, choose the skeleton with the most markers. Note: to allow the Arena software to know the difference between a user’s left arm and right arm, the triangles on either arm have to be unique (and thus different) from each other! If you notice that your recordings are somewhat glitchy, you may want to adjust the position of your markers slightly. Also, keep in mind that parts of your body may hide markers from certain cameras. Keep this in mind, and try to place markers in such a way that they’ll be visible to a lot of cameras. For more information, see the “The skeleton wizard” and subsequent tutorial videos from Optitrack at [4]

Exporting data to MotionBuilder

Once you’ve made a recording and want to export it to MotionBuilder, there are a few steps you have to take: First of all, the 2d take needs to be trajectorized. On the left side of the screen, under “Takes - 2D data”, right click on your take and select trajectorize. In the new window that appears, hit OK, as the defaults should be okay. Next, you can export the trajectorized data to a format MotionBuilder understands. Rightclick on the trajectorized take under “Takes - Trajectories”, and select “Export FBX”. Save the file somewhere. In MotionBuilder, you can now open this FBX file!

For more information, see the “Trajectorizing”, “Exporting data” and “FBX Export” tutorial videos at [5] Working with MotionBuilder is outside the scope of this document. If you know a lot about MotionBuilder, feel free to add some information to this wiki. If you don’t know a lot about MotionBuilder, ask someone who does for assistance, or take a look at the MotionBuilder tutorial videos.


One of the cameras displays ‘0’ on the LED display or has a LED display that’s turned off when the other cameras have numbers displayed. Make sure that all USB and SyncCables are connected correctly, check for loose connections, make sure that the USB hubs are powered. If you can’t find a problem with the connections, try inserting the USB hubs into a different USB port on the PC. If that doesn’t work either, try inserting the camera’s USB cable into a different port on the USB hub.

“Missing hardware key Message” while starting the Arena software.

Make sure that all 12 cameras are connected to the PC. Make sure that the USB hubs are connected and are powered.

Results of the calibration are not what you had expected.

Make sure that the value of the Data Points is 150 and the minimum amount of the cameras is the total of cameras or total cameras -1. Try to increase the data points or decrease the amount of cameras. When decreasing the amount of cameras the accuracy of capturing will go down. You can also try to decrease the Wand Data Speed in the Wand capture Window to Medium. If none of this works, it’s probably best to restart the entire calibration process. Make sure that you move the wand slowly across the room, and try to keep the marker on the wand in the field of view of as many cameras as possible.

Cannot find a T-pose or markers of a body part

Make sure that the marker count is equal to the marker count of the template you had selected. When recording the T-pose make sure that the system is capturing all the markers and that you are standing in a T-pose. If this does not work try to restart the calibration process.

The body of my character in Arena is spazzing out!

Because Arena uses a previously captured frame to calculate the positions of the next frame, it can sometimes happen that your character in Arena is behaving oddly. To fix this, try ‘unsticking’ the character by standing in a T-pose, waving your arms around, and moving around the room. If this happens often, try recalibrating the system and recreating the skeleton.