Active Marker Tracking
Main Page → Active Marker Tracking
This page provides instructions on how to set up and use the OptiTrack active marker solution.
- This guide is for OptiTrack active markers only. Third-party IR LEDs will not work with instructions provided on this page.
- This solution is supported for Ethernet camera systems (Slim 13E or Prime series cameras) only. USB camera systems are not supported.
- Motive version 2.0 or above is required.
- This guide covers active component firmware versions 1.0 and above; this includes all active components that were shipped after September 2017.
- For active components that were shipped prior to September 2017, please see the compatibility notes page for more information about the firmware compatibility.
The OptiTrack Active Tracking solution allows synchronized tracking of active LED markers using an OptiTrack camera system. The active tracking solution mainly consists of the Base Station and the active markers. The active markers can either be active markers on the Tag and/or markers on the active puck which can act as a single rigid body.
The Base Station connects to the camera system and sends out RF signals to the Tags, or pucks, allowing precise synchronization between camera exposure and illumination of the LEDs. Together, they allow Motive to recognize individual active markers in the software, and with labeled markers, more stable rigid body tracking can be achieved. The active markers will never be mislabeled and unique marker placements are no longer be required for distinguishing multiple rigid bodies.
Wiring the Components
- Active tracking is supported only with the Ethernet camera system (Prime series or Slime 13E cameras). For instructions on how to set up a camera system see: Hardware Setup.
- Connects to one of the PoE switches within the camera network.
- For best performance, place the base station near the center of your tracking space, with unobstructed lines of sight to the areas where your Active Tags will be located during use. Although the wireless signal is capable of traveling through many types of obstructions, there still exists the possibility of reduced range as a result of interference, particularly from metal and other dense materials.
- Do not place external electromagnetic or radio frequency devices near the Base Station.
- When Base Station is working properly, the LED closest to the antenna should blink in green when Motive is running. For more information: Base Station LED Indicators.
- Connect two sets of active markers (4 LEDs in each set) into the Tag.
- Power the Tag. Use a micro USB cable to connect the Tag to a power source.
- The power requirement is between 3.1V - 5.5V; measured at 100mA @ 5V with all LEDs on for 2ms every frame at 180 Hz.
- Once powered, you should be able to see the illumination of IR LEDs from the 2D reference camera view.
- Press the power button for 1~2 seconds and release. The top-left LED will illuminate in orange while it initializes. Once it initializes the bottom LED will light up green if it has made a successful connection with the base station. Then the top-left LED will start blinking in green indicating that the sync packets are being received.
- For more information, please read through the Active Puck page.
In order for Motive to reconstruct 3D points from the active LEDs, the following setting must be configured under the reconstruction settings:
- Marker Labeling Mode: Active Markers OR Active and Passive Markers
- Utilize Active Labels: True
Marker Labeling Mode
- (Default: Passive) The Marker Labeling Mode setting determines whether the point cloud engine reconstructs passive markers, active markers, or both passive and active markers. When Motive is configured to one of the active marker tracking modes, it will be indicated on the perspective view pane.
Utilize Active Labels
- (Default: True) This should be set to true for stable active marker tracking. When enabled, the point cloud engine uses only the active marker centroids that have the matching active IDs to create a reconstruction. Even if the tracking rays intersect within the allowable residual offset, any centroids with mismatching IDs will be rejected and will not contribute to the reconstruction.
Active Patten Depth
- (Default: 12) This setting sets the complexity of the active illumination patterns. When tracking a high number of rigid body, this may need to be increased to allow for more combinations of the illumination patterns on each marker. When this value is set too low, duplicate active IDs will be produced. In most applications, the default value can be used.
Active Marker Color
- (Default: white) This setting is located under the view tab in the Application Settings pane. The color assigned to this setting will be used to indicate actively labeled markers in Motive.
For tracking of the active LED markers, the following camera settings may need to be adjusted for best tracking results:
- For tracking the active markers, set the camera exposures a bit higher compared to when tracking passive markers. This allows the cameras to better detect the active markers. The optimal value will vary depending on the camera system setups, but in general, you would want to set the camera exposure between 400 ~ 750, microseconds.
- When tracking only active markers, the cameras do not need to emit IR lights. In this case, you can disable the IR settings in the Devices pane.
Active Markers in Motive
Once the above settings have been configured, active markers will be reconstructed and tracked in Motive. From the unique illumination patterns, each active marker gets labeled individually, and a unique marker ID gets assigned to the corresponding reconstruction in Motive. These IDs can be monitored in the Live-reconstruction mode or in the 2D Mode. To check the marker IDs of respective reconstructions, enable the Marker Labels option under the visual aids (), and the IDs of selected markers will be displayed in the 3D viewport. The marker IDs assigned to active marker reconstructions are unique, and it can be used to point to a specific marker within many reconstructions in the scene.
Rigid body definitions that are created from actively labeled reconstructions will search for specific marker IDs along with the marker placements to track the rigid body. Further explained in the following section.
Duplicate active frame IDs
Labels in Recorded 3D Data
In recorded 3D data, the labels of the unlabeled active markers will still indicate that it is an active marker. As shown in the image below, there will be Active prefix assigned in addition to the active ID to indicate that it is an active marker. This applies only to individual active markers that are not auto-labeled. Markers that are auto-labeled using a trackable model will be assigned with a respective label.
When a trackable asset (e.g. rigid body) is defined using active markers, it's active ID information gets stored in the asset along with marker positions. When auto-labeling the markers in the space, the trackable asset will additionally search for reconstructions with matching active ID, in addition to the marker arrangements, to auto-label a set of markers. This can add additional guard to the auto-labeler and prevents and mis-labeling errors.
Rigid Body Definition
Rigid body definitions created from actively labeled reconstructions will search for respective marker IDs in order to solve the rigid body. This gives a huge benefit because the active markers can be placed in perfectly symmetrical marker arrangements among multiple rigid bodies and not run into labeling swaps. With active markers, only the 3D reconstructions with active IDs stored under the corresponding rigid body definition will contribute to the solve.
Rigid Body Properties
If a rigid body was created from actively labeled reconstructions, the corresponding Active ID gets saved under the corresponding rigid body properties. In order for the rigid body to be tracked, the reconstructions with matching marker IDs in addition to matching marker placements must be tracked in the volume. If the active ID is set to 0, it means no particular marker ID is given to the rigid body definition and any reconstructions can contribute to the solve.
- Active Puck
- Information for Assembling the Active Tags
- Rigid Body Skeleton Markerset
- Active Finger Markerset
- Using active components between two camera systems