Multi-device setup
Multi-camera setups require two types of calibration: intrinsic parameters for each camera and extrinsic parameters for the scene.
- Intrinsic parameters: These are specific to the camera and remain the same as long as the resolution and zoom does not change. Intrinsic parameters can be reused across sessions.
- Extrinsic parameters: These define the relative positions of all devices for triangulating points between cameras. If any device’s position or rotation changes, recalibration is required. If the setup stays the same or you can match the positions exactly the calibration can be reused in future sessions. We perform extrinsic calibration for pairs of devices, so if there are more than two cameras used then finding all extrinsic parameters will be performed in multiple stages.
This software offers two methods to obtain both types of parameters:
- Charuco marker method: This method uses a printed sheet of Charuco markers. This is the preferred method - different setups may require different board sizes, see below.
- Measuring tape method: This method uses a measuring tape to measure the distances between devices and imaginary markers placed in the field view.
These methods can be used interchangeably. For instance, you can use the Charuco print method to obtain intrinsic parameters and the measuring tape method to obtain extrinsic parameters, or vice versa.
Resolution and framerate
Calibration is performed for a specific resolution and zoom level. This means that if you intend to record at various resolutions, you will need to perform calibration for each one separately.
AImation Studio can work with resolutions as low as 640x480. While it might seem that higher resolutions would always provide better results, this isn't always the case. Higher resolutions can create a zoom-in effect, increasing the area required (unless your device supports zoom functionality). However, improved image quality helps a lot in accurately estimating finger positions at a distance (if that's desired). Finding the right resolution may involve some trial and error to determine what best suits your needs.
In case of multi-device setup all devices must record at the same resolution and framerate.
When using Charuco method you’ll position a Charuco board in such a way that both cameras can see it at the same time. At the very least six frames need to be captured with both cameras being able to clearly see most of the markers.
One problem is that the further the devices are from each other, the farther back you’ll need to stand for the board to be visible in both camera views. As distance increases, the markers usually become less distinguishable and their detected position is less precise. For multi-camera calibration using this method, we recommend starting with at least an A3-sized print.
Note that intrinsic calibration does not have the same requirements since it involves calibrating the camera itself. You can bring the board closer to the device (or the device to the board) to capture images as needed.
This method typically requires at least two people, since it can be tricky to keep the measuring tape in place on the points being measured. You may find it useful to be able to mark objects in the field of view (for example some sticky notes or a masking tape).
Obtaining image for printing Generate charuco image ready for printing
Intrinsic calibration
Extrinsic calibration
