Introduction
This document discusses the definition of a tracking system and its use for virtual production.
What is a Tracking System and What is it Used for?
Tracking Systems are a combination of hardware and software used to determine the position (usually the position and rotation) of a given element (usually a tracking device) in space.
In Virtual Production, these systems are mostly attached to studio cameras to determine their position and rotation. This information (once the tracking system is calibrated) is extremely valuable for modeling dynamic, moving studio shots in the virtual environment.
The measuring of the tracking device's position and rotation happens relative to
- either external
- or internal reference points.
The measured data is then processed by
- a designated computer (part of the tracking system),
- a software (that can be installed on any computer),
- or in special cases by the "tracking device" (e.g. PTZ cameras that measure and process their rotation).
Difference of External and Internal Reference Points
External Reference Points
External reference points can be
- Active: the external reference points/devices measure the position and rotation of the tracking device.
- Passive: the tracking device uses the external points to measure its position and rotation.
Advantages:
- The precision of measurements can often be increased by adding more reference points.
- The use of external reference points can allow for covering bigger areas. Tracking at higher distances can be precise enough to hide imperfections.
- The tracking device can move freely in the tracking area (possibility of 6 Degrees of Freedom).
Disadvantages:
- They require a higher number of hardware to operate (increased installing time)
- They are more prone to receive noise from their environment, which can interfere with the precision of measurement (e.g., people blocking the view of reference points, reference points moving when installed on less-than-stable tripods, etc).
Internal Reference Points
Internal reference points are within the tracking device itself. This solution measures the movement of the internal hardware components, such as the movements of cogwheels. These can be
- manually moved (the system can only measure the movement but cannot execute it)
- robotized (e.g., servo engines)
- or a combination of both (e.g,. rocker arms, where the panning and tilting of the arm happens manually, but the panning and tilting of the head is robotized)
Advantages:
- Although the system internally may be more complex (higher number of moving parts), it usually packages the components better (lower number of individual hardware), thus, the hardware setup time can be shorter.
- It is not sensitive to changes in the environment (the measurement happens inside the hardware, in a shielded area)
- Usually processes the measured data internally (no need for dedicated computers/dedicated computers are built-in)
Disadvantages:
- The precision of the measurements depends on the system's intrinsic limitations, it cannot be improved.
- The tracking device only has a limited range of movements (6 Degrees of Freedom is only partially available, if available at all).
- In some cases at higher distances, the measurements' imperfection can become increasingly noticeable.
- In some cases, bigger ranges of movement will result in bigger tracking systems.
What is a Lens Encoder and What Is It Used for?
Lens encoders measure the position of the camera lens's rings. Most camera lenses have two or three rings to control their lens parameters. These are:
- Zoom ring (only present on zoom lenses, adjusts the focal length),
- Focus ring (adjusts the focus distance),
- Aperture ring (adjusts the amount of light that passes through the lens).
Using lens encoders, we can extend the capabilities of a tracking system to track the changes in the camera lens settings. This can allow for the modeling of zooming, focusing, and aperture changes in the virtual environment.
NOTE: Many modern tracking systems have already incorporated these devices.
NOTE: Aximmetry allows for the combined use of tracking systems (without lens encoders) with third-party lens encoders.
Notable Mentions
You can learn more about the tracking systems supported by Aximmetry by referring to the following document:
Tracking Systems
