Is there any relevant content on CBCT system calibration in RTK?

Recently, while studying CBCT calibration, I can only calculate the projection matrix from the position of the steel ball in one projection image and the mold. I can calculate a projection matrix for each projection image, but how can I combine multiple projection images to calculate?

Sorry but I do not fully understand the question. There should be one projection matrix (and image) per source position. RTK’s geometry object, rtk::ThreeDCircularProjectionGeometry can store all them, simply use AddProjection for each one. How would you like to combine them?