Rigid Frames


Rigid Frames are designed to be objects whose shape does not change, and as the name suggests "rigid", such as a set piece like a table or box. Rigid Frames must have at least 3 LEDs assigned in order for a solution to be created for the frame. There is no limit to the number of LEDs that can be assigned to a rigid frame. If at any point less than 3 LEDs are visible for the specific rigid frame, tracking will stop. This section outlines the creation of a rigid frame.

Creating a Rigid Frame

Create a rigid frame in the Body Frames widget. First, assign an ID to the frame.

To assign an ID to a frame.

  1. Enter a numerical ID for the frame in the Frame ID box (Beacon ID) at the bottom of the Body Frames widget.
  2. On the drop-down list, click Rigid Body.
  3. Click the green button.
  • Result: The Rigid Frame is created and added to the list in the widget.

Once the frame is created, you may double-click and type a new name on the default name cell, and press ENTER. By default, a Rigid Frame is given a name of 'RF(ID)'. 

Assigning LEDs to a Rigid Frame

Assign LEDs to a rigid frame by dragging individual beacons from the global Beacons widget to the Frame LEDs widget with a rigid frame selected in the Body Frames widget.

You must place the LEDs in the correct order on the object as well as in the Frame LEDs widget because the first three LEDs assigned to a rigid frame defines the orientation of the frame.

  • The first LED corresponds to the origin of the local coordinate system of the object.
  • The second LED corresponds to the positive x-axis.
  • The third LED is special because it can be placed anywhere, but it defines the location of the positive y-axis in the following way:
    • Placing the third LED somewhere in the same plane as LED 1 and LED 2, and taking the cross product of the vectors from the origin to LED 2, and the origin to LED 3 will define the positive z-direction of the local coordinate system of the rigid body. Use the right-hand rule to determine the cross-product.
    • To perform the right-hand rule:
      1. Place the side of the right hand, and place it along the line from the origin (LED 1) to the positive x-axis (LED 2).
      2. Curl the fingers of the right hand towards the line from the origin (LED 1) to LED 3.
      3. The direction where the thumb points is the positive z-axis.

Once the first three LEDs are placed, any further LEDs added to the rigid body can be placed anywhere and will be used as additional tracking points for the object, but are not required.


Constructing the Frame

Once the LEDs have been assigned, the frame can be initialized and the solution can be calculated. Click Construct Frame in the Rigid Frame Construction widget to initialize and calculate the solution. If the original solution of the rigid frame changes, BlackTrax will attempt to adjust the existing solution accordingly. This will change the status of all current frames with LEDs assigned to them from "Done" to a list of the LEDs that have not yet appeared (visible to the tracking system). Click the Apply Changes button to send all ready frames to the global Beacons widget(s), and allow them to be assigned to a trackable. Click the Reset All Frames button to remove the solution from all Frames, but not delete them. You must click Apply Changes.


Set Home

In most situations, it is necessary to align the Rigid Frame's orientation to an acceptable 'home' position. A home position is where the object will be 0,0,0 for the Roll, Pitch, and Yaw respectively. You can manually perform this action, but it is much easier to let BlackTrax determine this for you.

To use the set home function

  1. Align the real world object along the same plain as the world coordinate system (ensure your X, Y, and Z directions match where you set the ground plane. An example is to set the front face of the object facing -Y).
  2. Select your desired Frame.
  3. Click Set Home.

Result: Your object will now be orientated with Roll at 0, Pitch at 0, and Yaw at 0. The object will rotate in the same way that the real world coordinate system would rotate. 

Once the object is 'homed', it is easier to offset the centroid and orientation of the Rigid Frame (although you may do this before you home the object, if desired). Enter the required values into the X, Y, and Z fields for the centroid (in meters), and Roll, Pitch, and Yaw fields for Orientation (in degrees). These settings will be applied automatically, based off the time set under System Configuration>Frame Calibration>Updating offsets interval (seconds). By default, this is set to update 0.5 seconds after the values are updated.

Note: You do not need to click Apply Changes when doing centroid and orientation offsets or setting the home orientation.

Rigid Body