How to initialize the reconstruction with GPS and IMU data?

[Vadim3D]

Hi,
What is the best way to initialize bundle adjustment with known camera positions and orientations (by known, I mean measured e.g by GPS and IMU)?

When using the import reference coordinates in the reference panel "Reference panel -> import -> import cameras positions and orientations from csv file" and then align, What does it do?

Is that initializes the alignment (initializes bundle adjustment)?
Or is that tries to put the reconstructed cameras close to the imported reference coordinates?

Many thanks,
Vadim