Calibration

Page Overview

Watch the Theia Tutorial on how to perform the calibration:

Lay the chessboard on the ground.

Note: The chessboard has to be fully in view in a minimum of three cameras, but try having it visible in as many views as possible. Your origin will be set where the two blue squares intercept, so be sure to align the intercept with your desired origin.
Leave the volume, and press record, having the first few seconds of the recording be just the chessboard with as few obstructions as possible.
Pick up the chessboard and start showing the chessboard to groupings of three cameras.

Note: Move slow and deliberately to avoid motion blur. A minimum of three cameras must see the board at all times, so think of showing the board to groupings of three, with an overlapping fourth camera during transitions. Vary the angle of the board while calibrating.
Once you have gone around and are confident every camera has seen the chessboard, set the chessboard back on the ground where you want your origin to be set.

Note: later on you will be able to choose what frame you want to use as your origin (either a starting frame when the board is flat on the ground or one at the end when you set it back down) so it’s not mandatory to line it back up with the origin at this step, but it is good practice so that there is a “backup” origin frame.

At least three cameras must see the calibration board at all times.
When the board is placed on the ground, the intercept of the two blue squares is where the origin will be.
Move slowly and deliberately, too fast of a movement will cause motion blur and may cause the calibration to fail.
Make sure the room is well lit.
Make sure there are no mirrors around (in view of the cameras).
Ensure only one chessboard is visible during a calibration. Any additional chessboard will cause a processing error in detecting a calibration.

To learn how to process the calibration in Theia, see Organizing and Processing Data

There are many reasons why a calibration may fail. A few of the most common reasons include:

Motion blur was caused by the calibration being performed too quickly.
The person perfoming the claibration did not show the board to groupings of three with an overlapping fourth camera during transitions.
The camera is too far from the calibration board.
There was too much glare on the board.
The volume was too dark and the chessboard could not be seen clearly.
In some angles/lighting, the blue squares may appear as black, adjust camera angles/lighting to make the blue look more blue.
When the board was on the floor, cameras we not angled such that three cameras have a good view of the board (sometimes a camera may need to be lifted slightly higher to get a better view of the board).
There was a mirror/highly reflective surface in view of camera(s).
There were multiple calibration boards detected within the recording.
The view of the calibration board was obstructed by something.
If the calibration goes through but the origin is tilted, check that your calibration board isn’t warped.
If the calibration goes through but the origin frame is different from the one you selected (oftentimes resulting in a tilted origin), this means that the chessboard was not detected by a minimum of three cameras in the frame that you chose.