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Human Extrinsic Calibration


To enable animation capture in Genesis, you must first calibrate the system using either a checkerboard or a human subject. In this article, we’ll walk you through the human calibration process.

Recording a Human Calibration

  1. Start a recording.
  2. Stand in the centre of the capture area.
  3. Stand still in a Y pose for 2 seconds before starting the calibration sequence.
    1. Note: If you are not using a synchronised camera such as a Z Cam, you will need to clap three times above your head before performing the Y-pose. This will generate a distinct audio peak, which can then be used as a synchronisation point.
  4. Still holding the Y-pose, walk from the centre of the capture area toward each camera, stopping at the edge of the volume. Keep your face directed toward the camera throughout, pausing at the edge before walking naturally back to the centre.
  5. Ensure that you walk towards each camera, until you are as close as possible whilst still fully framed. This will ensure the area that you calibrate will represent the area that you will do your performance within.
  6. Repeat this motion walking to each camera, then backwards to the centre, before moving on to the next.
  7. If using less than 4 cameras, walk around the perimeter of the volume to ensure the system has an accurate understanding of the perimeter of the capture volume. (The perimeter you define, will be used to ensure only the desired actors are tracked during action takes)
  8. Now finish the recording.
    1. At this stage, we recommend measuring the height of your actor and noting it down, you'll need it later when you process the calibration! Their height should not include the footwear they are wearing.
    2. We always recommend doing an extra calibration at the end of your session, just in case a camera was moved during the session.

Here is an example

Note: This example action was taken using the Z-Cams. 

In this example, you would enter the following sequence times:

  • Sync method: Timecode
  • Y-pose sequence start time: 00:01
  • Y-pose sequence end time: 01:19

 

Essential Precautions

  • Make sure only the actor (i.e no other people) are in the capture volume, or holding a Y-pose during the calibration otherwise the system may track the wrong actor.
  • If the cameras are moved (even slightly) at any point during the shoot, a new calibration will be required for optimal results.

What is the purpose of the calibration?

The calibration process provides the system with a few crucial pieces of information:

  1. The positions and orientations of your cameras:
    • The system needs to determine this information about the cameras so that it can correctly interpret the location of the actors seen in the footage during the action takes.
  2. The scale of the 3D worldspace:
    • By knowing the height of the calibrating actor, the system can determine their position by triangulating their keypoints in the footage from each camera. Based on this, the system will be able to automatically determine the size and position of the actors seen in the action takes.
  3. The origin on the 3D worldspace:
    • When you process your calibration, you enter the start time of the Y-pose sequence. The system use the location and orientation of the actor at this time, to lock in the location and orientation of the origin. The animations for all action takes using this calibration will then be positioned with respect to this origin
  4. The perimeter of the capture volume (check out the below visualisation):
    • What The perimeter of the capture volume is used to determine who is tracked during your action takes. When you process an action take, you will enter the start and end time and the number of actors to be tracked. In the first frame of this window, the system will search for the given number of actors within the perimeter, to ensure that only the desired actors are tracked. If the desired actors are stood outside this perimeter at this time, they will not be tracked. If any actors enter this area after the start time, they will not be tracked.
    • How The perimeter is created automatically, determined by the furthest locations the actor moves from the origin. As the actor walks towards each camera, these locations will be logged and will be used to define the perimeter of a convex hull, otherwise known as the capture volume. If less than 4 cameras are used, we recommend walking around the perimeter of the volume after the usual sequence (still in a Y-pose), so that the perimeter has enough keypoints to ensure it doesn't cut off any corners of your capture volume.