The Builder pane is used for creating and editing trackable models, also called trackable assets, in Motive. In general, rigid body models are created for tracking rigid objects, and skeleton models are created for tracking human motions.
When created, trackable models store the positions of markers on the target object and use the information to auto-label the reconstructed markers in 3D space. During the auto-label process, a set of predefined labels gets assigned to 3D points using the labeling algorithms, and the labeled dataset is then used for calculating the position and orientation of the corresponding rigid bodies or skeleton segments.
The trackable models can be used to auto-label the 3D capture both in Live mode (real-time) and in the Edit mode (post-processing). Each created trackable models will have its own properties which can be viewed and changed under the Properties pane. If new skeletons or rigid bodies are created during post-processing, the Take will need to be auto-labeled again in order to apply the changes to the 3D data.
On the Builder pane, you can either create a new trackable asset or modify an existing one. Select either rigid body or skeleton at the bottom of the pane, and then select whether you wish to create or edit. Each feature will be explained in the sections below.
For creating rigid bodies, select the rigid body option at the bottom and access the Create tab at the top. Here, you can create rigid body asset and track any markered-objects in the volume. In addition to standard rigid body assets, you can also create rigid body models for head-mounted displays (HMDs) and measurement probes as well.
Step 1.
Select all associated rigid body markers in the 3D viewport.
Step 2.
On the Builder pane, confirm that the selected markers match the markers that you wish to define the rigid body from.
Step 3.
Click Create to define a rigid body asset from the selected markers.
Other ways to create a rigid body
You can also create a rigid body by doing the following actions while the markers are selected:
Prespective View (3D viewport): While the markers are selected, right-click on the perspective view to access the context menu. Under the Rigid Body section, click Create From Selected Markers.
Hotkey: While the markers are selected, use the create rigid body hotkey (Default: Ctrl +T).
Step 4.
Once the rigid body asset is created, the markers will be colored (labeled) and interconnected to each other. The newly created rigid body will be listed under the Assets pane.
If the rigid bodies, or skeletons, are created in the Edit mode, the corresponding Take needs to be auto-labeled. Only then, the rigid body markers will be labeled using the rigid body asset and positions and orientations will be computed for each frame.
This feature can be used only with HMDs that have the OptiTrack Active HMD clips mounted.
For using OptiTrack system for VR applications, it is important that the pivot point of HMD rigid body gets placed at the appropriate location, which is at the root of the nose in between the eyes. When using the HMD clips, you can utilize the HMD creation tools in the Builder pane to have Motive estimate this spot and place the pivot point accordingly. It utilizes known marker configurations on the clip to precisely positions the pivot point and sets the desired orientation.
Steps
First of all, make sure Motive is configured for tracking active markers.
Open the Builder pane under View tab and click Rigid Bodies.
Under the Type drop-down menu, select HMD. This will bring up the options for defining an HMD rigid body.
If the selected marker matches one of the Active clips, it will indicate which type of Active Clip is being used.
Under the Orientation drop-down menu, select the desired orientation of the HMD. The standard orientation used for streaming to Unity is +Z forward and Unreal Engine is +X forward, or you can also specify the expected orientation axis on the client plugin side. For use with the OpenVR driver, please set the HMD rigid body to Z-axis forward orientation.
Hold the HMD at the center of the tracking volume where all of the active markers are tracked well.
Select the 8 active markers in the 3D viewport.
Click Create. An HMD rigid body will be created from the selected markers and it will initiate the calibration process.
During calibration, slowly rotate the HMD to collect data samples in different orientations.
Once all necessary samples are collected, the calibrated HMD rigid body will be created.
For using OptiTrack system for VR applications, it is important that the pivot point of HMD rigid body gets placed at the appropriate location, which is at the root of the nose in between the eyes. When using the HMD clips, you can utilize the HMD creation tools in the Builder pane to have Motive estimate this spot and place the pivot point accordingly. It utilizes known marker configurations on the clip to precisely place the pivot point set the desired orientation.
For more information: Measurement Probe Kit Guide
Steps: Probe Calibration
Open the Builder pane under View tab and click Rigid Bodies.
Bring the probe out into the tracking volume and create a rigid body from the markers.
Under the Type drop-down menu, select Probe. This will bring up the options for defining a rigid body for the measurement probe.
Select the rigid body created in step 2.
Place and fit the tip of the probe in one of the slots on the provided calibration block.
Note that there will be two steps in the calibration process: refining rigid body definition and calibration of the pivot point. Click Create button to initiate the probe refinement process.
Slowly move the probe in a circular pattern while keeping the tip fitted in the slot; making a cone shape overall. Gently rotate the probe to collect additional samples.
After the refinement, it will automatically proceed to the next step; the pivot point calibration.
Repeat the same movement to collect additional sample data for precisely calculating the location of the pivot or the probe tip.
When sufficient samples are collected, the pivot point will be positioned at the tip of the probe and the Mean Tip Error will be displayed. If the probe calibration was unsuccessful, just repeat the calibration again from step 4.
Once the probe is calibrated successfully, a probe asset will be displayed over the rigid body in Motive, and live x/y/z position data will be displayed under the Real-time Measurement section in the Measurements pane.
Steps: Sample Collection
Under the Tools tab, open the Measurements pane.
Place the probe tip on the point that you wish to collect.
Click Take Sample on the Measurement pane.
A virtual reconstruction will be created at the point, and the corresponding information will be displayed over the measurement pane. The sampled points will also be saved in the exported onto the project directory.
Collecting additional samples will provide distance and angles between collected samples.
Sampling 3D points using the measurement probe.
Using the Builder pane, you can also modify existing rigid body assets. For editing rigid bodies, select the rigid body option at the bottom of the Builder pane and access the Edit tab at the top. This will bring up the options for editing a rigid body.
Using the Rigid Body Refinement tool for improving asset definitions.
This feature is supported in Live Mode only.
Rigid body refinement tool improves the accuracy of rigid body calculation in Motive. When a rigid body asset is initially created, Motive references only a single frame for defining the rigid body definition. The rigid body refinement tool allows Motive to collect additional samples in the live mode for achieving more accurate tracking results. More specifically, this feature improves the calculation of expected marker locations of the rigid body as well as position and orientation of the rigid body itself.
Steps
Under View tab, open the Builder pane.
Select the Rigid Bodies option at the bottom of the pane and go to the Edit tab.
In Live mode, select an existing rigid body asset that you wish to refine.
Hold the selected rigid body at the center of the capture volume so that as many cameras as possible can clearly capture the markers on the rigid body.
Press Start Refine in the Builder pane and the
Slowly rotate the rigid body to collect samples at different orientations.
Once all necessary samples are collected, the refinement results will be displayed.
The Probe Calibration feature under the rigid body edit options can be used to re-calibrate a pivot point of a measurement probe or a custom rigid body. This step is also completed as one of the calibration steps when first creating a measurement probe, but you can re-calibrate it under the Edit tab.
Steps
In Motive, select the rigid body or a measurement probe.
Bring out the probe into the tracking volume where all of its markers are well-tracked.
Place and fit the tip of the probe in one of the slots on the provided calibration block.
Click Start
Once it starts collecting the samples, slowly move the probe in a circular pattern while keeping the tip fitted in the slot; making a cone shape overall. Gently rotate the probe to collect additional samples.
When sufficient samples are collected, the mean error of the calibrated pivot point will be displayed.
Click Apply to use the calibrated definition or click Cancel to calibrate again.
Options for translating and rotating the rigid body pivot point.
The Edit tab is used to apply translation or rotation to the pivot point of a selected rigid body. A pivot point of a rigid body represents both position (x, y, z) and orientation (pitch, roll, yaw) of the corresponding asset.
You can also use the Gizmo tools to quickly make modify the pivot point of a rigid body
Location
Use this tool to translate a pivot point in x/y/z axis (in mm). You can also reset the translation to set the pivot point back at the geometrical center of the rigid body.
Orientation
Use this tool to apply rotation to the local coordinate system of a selected rigid body. You can also reset the orientation to align the rigid body coordinate axis and the global axis.When resetting the orientation, the rigid body must be tracked in the scene.
The OptiTrack Clip Tool basically recalibrates HMDs with OptiTrack HMD Clips to position its pivot point at an appropriate location. The steps are basically the same as when first creating the HMD rigid body.
This feature is useful when tracking a spherical object (e.g. ball). It will assume that all of the markers on the selected rigid body are placed on a surface of a spherical object, and the pivot point will be calculated and re-positioned accordingly. Simply select a rigid body in Motive, open the Builder pane to edit rigid body definitions, and then click Apply to place the pivot point at the center of the spherical object.
To create skeletons in Motive, you need to select the skeleton option at the bottom of the Builder pane and access the Create tab at the top. Here, you select which Skeleton Marker Set to use, choose the calibration post, and create the skeleton model.
Defining skeleton from a skeleton Marker Set.
Step 1.
From the skeleton creation options on the Builder pane, select a skeleton marker set from the Marker Set drop-down menu. This will bring up a skeleton avatar displaying where the markers need to be placed on the subject.
Step 2.
Refer to the avatar and place the markers on the subject accordingly. For accurate placements, ask the subject to stand in the calibration pose while placing the markers. It is important that these markers get placed at the right spots on the subject's body for the best skeleton tracking. Thus, extra attention is needed when placing the skeleton markers.
The magenta markers indicate the segment markers that can be placed at a slightly different position within the same segment.
Step 3.
Double-check the marker counts and their placements. It may be easier to use the 3D viewport in Motive to do this. The system should be tracking the attached markers at this point.
Step 4.
In the Builder pane, make sure the numbers under the Markers Needed and Markers Detected sections are matching. If the skeleton markers are not automatically detected, manually select the skeleton markers from the 3D perspective view.
Step 5.
Select a desired set of marker labels under the Labels section. Here, you can just use the Default labels to assign labels that are defined by the markerset template. Or, you can also assign custom labels by loading previously prepared marker-name XML files in the label section.
Step 6.
Next step is to select the skeleton creation pose settings. Under the Pose section drop-down menu, select the desired calibration post you want to use for defining the skeleton. This is set to the T-pose by default.
Step 7.
Ask the subject to stand in the selected calibration pose. Here, standing in a proper calibration posture is important because the pose of the created skeleton will be calibrated from it. For more details, read the calibration poses section.
Step 8.
Click Create to create the skeleton. Once the skeleton model has been defined, confirm all skeleton segments and assigned markers are located at expected locations. If any of the skeleton segment seems to be misaligned, delete and create the skeleton again after adjusting the marker placements and the calibration pose.
In Edit Mode
If you are creating a skeleton in the post-processing of captured data, you will have to auto-label the Take to see the skeleton modeled and tracked in Motive.
Virtual Reality Marker Sets
Skeleton Marker Set for VR applications have slightly different setup steps. See: Rigid Body Skeleton Marker Set.
To create skeletons in Motive, you need to select the skeleton option at the bottom of the Builder pane and access the Edit tab at the top.
Existing skeleton assets can be recalibrated using the existing skeleton information. Basically, the recalibration recreates the selected skeleton using the same skeleton markerset. This feature recalibrates the skeleton asset and refreshes expected marker locations on the assets.
To recalibrate skeletons, select all of the associated skeleton markers from the perspective view along with the corresponding skeleton model. Open the Builder pane, and open the Edit tab while Skeleton option is selected at the bottom. Make sure the selected skeleton is in a calibration pose, and click Recalibrate. You can also recalibrate from the context menu in the Assets pane or in the 3D Viewport.
Skeleton recalibration do not work with skeleton templates with added markers.
Assets pane: While the markers are selected in Motive, click on the add button in the Assets pane.
