calibration; how to use known intrinsics and what is the origin of the coordinate system?

[MaudvdBogaart]

Good afternoon,
I have two questions regarding calibration via anipose;

1. Is it possible to retrieve the extrinsics (via the anipose calibrate command) when providing the intrinsics? We already have the correct intrinsics of the camera, so we would like to determine the extrinsics of every camera (using the correct intrinsics, which we already have and which should not be determined by anipose).

Could this be 'solved' by using a calibration.toml file with the correct intrinsics and name it 'calibration_init.toml'? And add the calibration_init variable to the config.toml like this? ;
[calibration]
calibration_init = "calibration_init.toml"

2. what is taking as the origin of the coordinate system? Is this a specific corner on the calibration pattern in the first frame of the calibration video of the first camera?

Any help or suggestions are welcome! Thanks in advance!