Active Marker Tracking

Main Page → Active Marker Tracking

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Page Scope

This page provides instructions on how to set up and use the OptiTrack active marker solution. Note that this guide is specific only to the pre-programmed OptiTrack active LED marker kit.

Additional Note

• This guide is for OptiTrack active marker users 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.
• This guide covers active component firmware versions 1.0 and above.
• For active components that were shipped prior to September 2017, please see the compatibility notes page for more information about the firmware compatibility.
• Motive 2.0 or above is required.

Overview

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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 the unique illumination patterns and assign unique IDs to respective active markers in the software, and with individually labeled markers, more stable rigid body tracking can be achieved; the markers will never be mislabeled and unique marker placements are no longer be required for distinguishing multiple rigid bodies.

Hardware Setup

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Required Components

Name	Image
Base Station Sends out radio frequency signals for synchronizing the active markers. Powered via PoE. Must be connected to one of the switches in the camera network.
Tag Connects to a USB power source and illuminates the active LEDs. Receives RF signals from the Base Station and correspondingly synchronizes illumination of the connected active LED markers.
Active LEDs Emits 850 nm IR light. 4 active LEDs in each bundle and up to two bundles can be connected to each Tag. (8 Active LEDs (4(LEDs/set) x 2 set) per Tag) Size: 5 mm (T1 ¾) Plastic Package, half angle ±65°, typ. 12 mW/sr at 100mA
Active Pucks A standalone trackable object can provide 6 DoF tracking information for any object to which it is applied. Carries a factory installed Active Tag with 8 LEDs and a rechargeable battery with up to 10 hour run time on a single charge. The active pucks can also be attached to hands and feet of a player for rigid body skeleton tracking.

Wiring the Components

Camera System

• 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.

Base Station

• 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.

Tag Setup

• 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.

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  Base station setup.
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  Assembled Tags

Puck Setup

• 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.

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  Puck initializing. Top-left: Orange.
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  Connected to base station and receiving sync packets

Motive Settings

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Application Settings

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.

Camera Settings

For tracking of the active markers, the following camera settings may need to be adjusted.

Camera Exposure

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.

IR LEDs

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.

2D Filter: Grayscale Floor

For tracking active markers, set the grayscale floor in the camera 2D filter settings to 32. This allows cameras to better see the active markers.

2D Filter: Object Margin

Under the 2D filter settings, set the Object Margin to 2. This allows cameras to better detect markers that are close-by. This is beneficial especially for tracking active markers on the pucks.

Active Markers in Motive

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Active Labels

Unique marker IDs (289, 274, 265) assigned to the active markers

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 For the active label to properly work, it is important that each marker has a unique active IDs. When there are more than one markers sharing the same ID, there may be problems when reconstructing those active markers. In this case, the following notification message will show up. If you see this notification, please contact support to change the active IDs on the active markers.

Labels in Recorded 3D Data

Unlabeled Markers

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.

Auto-labeled Markers

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

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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.

Troubleshooting

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› Q : Active markers are flickering from both the 3D viewport in Motive.

A:

• Make sure Motive is set to tracking Active markers under the reconstruction settings. The Marker Labeling Mode must be set to either Active Markers Only or Active and Passive Markers.
• If flickering occurs on markers of a specific Tag only, try power cycling it. If it tracks fine afterward, the Tag is using v0.8 firmware.