Data collection guide for Overlapping Camera Calibration (Multiple-Targets)

Display surface

• The surface used for displaying the charuco board should be completely flat, i.e. zero curve

• We should select a surface with zero/minimal edge, i.e. non display area

• There should be no distortion or changes made by the display to the charuco boards while displaying if using a digital display

• The brightness/ligth reflected from the surface should be balanced to have clear image. not too low or not too high.

Target

• The target should be generated to match perfectly fit the surface to maximize the target display and get the measurements precise.

• All the charuco boards should be of different dictionaries for better detection

• Use the targets in pdf form to avoid any scaling done by the display app if using a digital display

Surroundings and Setup

• The room should be lit in a balanced way such that the clarity of captured images is maximum

• The complex dictionary should be nearer for better detection. The order of preference is 7×7 > 6×6 > 5×5 > original.

• Place the camera such that to 1. Avoid including areas without charuco displayed. 2. The number of common detected points between the left and right camera is maximum

• The Angles between the targets should be such that it covers the complete field of view of both the cameras depending on the distance between the monitor and the cameras and size of the targets

• The cameras should be placed on a stable platform and image clicks should be triggered wireless/ with utmost care to avoid any disturbance that can change the setup's ground truth.

Beneath are examples of good Setup images:

Beneath are examples of bad data collection:

There is lot of gap which lessens the number of common corners detected. The lighting is not uniform which might not give the best corner detection. There is padding due to which you have to measure squares manually which might add error in the measurement.

Square Length Calculation when using monitors

These formulas are useful when the charuco board generated fits precisely to the display used both in length and width with no padding

$$SquareSize = \sqrt{(\dfrac {total display area}{total number of squares})}$$

$$TotalDisplay Area = {LengthOfMonitorArea} \times {WidthOfMonitorArea}$$

​If the manufacturer doesn't provide the length and width of the display but provides the diagonal length (dl) and the ratio of the length and width ( i.e L : W) then the total display area is

$$\dfrac{(L \times W\times {dl^2})}{({{L^2}+{W^2}})}$$

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