Set initial transformation using only .pcd files

[FrederikPlahl]

Thanks for the great tool!
I'm trying to calibrate the pc from a LiDAR to the pc from a realsense camera. I started with using the whole pc from ROS bag files, but the calibration did not work correctly because one recorded the ceiling and one the floor resulting in overlaying both pcs at those points. That's why I moved on to cropped pcs stored in .pcd files. But here the calibration fails completely. With the error:

[multi_lidar_calibrator-1] Max core number: 0
[multi_lidar_calibrator-1] Num vertices: 2
[multi_lidar_calibrator-1] Max clique lower bound equals to zero. Abort.
[multi_lidar_calibrator-1] Max Clique of scale estimation inliers: 
[multi_lidar_calibrator-1] Clique size too small. Abort.
[multi_lidar_calibrator-1] Starting scale solver (only selecting inliers if scale estimation has been disabled).
[multi_lidar_calibrator-1] Scale estimation complete.
[multi_lidar_calibrator-1] Max core number: 0
[multi_lidar_calibrator-1] Num vertices: 2
[multi_lidar_calibrator-1] Max clique lower bound equals to zero. Abort.
[multi_lidar_calibrator-1] Max Clique of scale estimation inliers: 
[multi_lidar_calibrator-1] Clique size too small. Abort.
[multi_lidar_calibrator-1] [ERROR] [1725032869.040792930] [multi_lidar_calibration_node]: no calibration within given threshold possible, try reducing the thershold, make more overlap between the point clouds or provide more accurate initial transformation

How can I give an initial transformation without using TF from ROS?

For reference, here are the pcs that I want to match: