Multi-device setup
Multi camera setups require two types of calibrations, intrinsic parameters of each camera and extrinsic parameters of the setup.
With intrinsic parameters we have it quite easy, as long as the resolution of the device does not change, we do not need to recalibrate the device and as long as we have the file on disk, we can later re-use it.
With extrinsic parameters the situation is slightly different, this type of calibration has to be performed whenever one of the devices changes its position OR orientation in the daisy chain. We use this data to perform triangulation of points between each camera for better motion capture results.
If the devices are stationary or you've marked the positions and orientation they're supposed to be in, the calibration file can be re-used, meaning it's good to take pictures of your setup or physically mark where the devices are supposed to be.
This software offers two methods of obtaining both parameters:
- Using a sheet of paper that has charuco markers printed on it, print can be used for both intrinsic and extrinsic calibration but has different requirements.
- Using measuring tape and measuring distances between each device and distances to imaginary marker for extrinsic and measuring distances between two points and camera for intrinsic calibration. In some cases this might require 2 people, extra person to hold one end of the tape.
Methods can be used interchangeably, we can use charuco print to obtain intrinsic parameters and use a measuring tape method to obtain extrinsic parameters of the system and vice versa.
Print method and board requirements
When using Charuco print for extrinsic calibration, it's important to consider the distance between devices and the size of the print. The calibration process requires us to capture a pair of images at various angles, with the calibration board occupying most of the view in both devices. A greater distance between devices means we have to stand further away from the cameras, which can make the squares and markers more difficult to detect, requiring a larger board with larger markers. Typically, when devices are about 40cm apart, an A4-sized format becomes too small for devices recording at a resolution of 640x480; however, this threshold varies with the image quality, resolution used, and camera settings. Additionally during recording the print should be rigid which also becomes a problem with bigger boards.
When calibrating intrinsic parameters, the size of the board does not matter as much; we can simply move closer to the board and maneuver the device around it.
Recommended way to calibrate is to use charuco print method when possible.
A4 format for distances between devices up to 40cm,
A3 format for distances between 40cm - 1m
Anything above we recommend performing measuring tape calibration for extrinsic
When placing the devices, the minimum distance apart required is roughly 5cm.
Generate charuco image ready for printing
Intrinsic calibration
Extrinsic calibration
Loading calibration files into devices
- Click wrench button under camera icon in Recording tab
- Load extrinsic calibration into system
