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Easy SCX Stereo Camera Calibration

Note that all below instructions assume that you are using CP version 10.0.9.7 or higher

available as of 04/01.2024

Please note: Other than scaling, calibration is only really intended for fine tuning.

If you are experiencing major ball carry discrepancies, then the cause most probably lies elsewhere.

What is stereo camera calibration?

As each individual camera installation will be slightly different,

(i.e. cameras are mounted at different heights, different spacing, off-line and slightly skewed)

the main objective is to correct the factory set default calibration tables so that they match the particular users camera installation.

This page is mainly concerned with Disparity to ball height conversion.

Camera alignment instructions are dealt with on another page

Click above button to read more...

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Easy SCX Stereo Camera Calibration Steps

Step 1

This sets the ball to ground zero with near zero disparity

Step 2

Check to see that the ball is at or very close to ground zero

Step 3

The calibration table is used to convert stereo disparity values to real ball height off the ground

Step 4

Note: when raising the ball on the mat, use a dark non-reflective object to place the ball on

so that only the ball is detected.

You can use books covered with a dark material to elevate the ball to the desired height.

A black mouse pad is good to cover the books so that only the ball appears bright.

Note that ball height is measured from the bottom of the ball to the floor.

Ensure you click on the Soft Trigger in both the left and right cameras for every height and disparity reading

Step 5

Step 6

The stereo calibration table has 150 disparity entries that are split into 6 pages.

Each page has its own page height adjust value.

You can also adjust each disparity height value individually but this rarely required

Step 7

As the SCX camera ball height detection will effectively never go over 27 cm,

there is no requirement to adjust more than the first 3 pages of the table.

Done!

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Stereo camera Disparity explained

The above diagram explains the basic stereoscopic principles.

If the two 2 stereo cameras are aimed precisely at the center line and a ball is placed at floor level, the images of the will appear on top of each other.

The disparity of the ball is then zero (or near zero) and this is known as the "Converging point"

When the ball is elevated, the images of the ball in the camera frames will start to separate. The distance the ball images are apart is the "Disparity".

Using a "disparity to ball height" table, the exact height of the ball can be determined.

Knowing where the ball was before ball strike the ball LA and path can be determined.

Ball path is simply derived from the divergence the center of the disparity distance is from the center line.

i.e. a perfectly straight shot would show that the 2 ball images are the exact same distance from the center line.