Questions about Camera XYZ coordinates and world coordinates

[an198317]

Hi all,

The more I used Agisoft PhotoScan Pro, the less I feel like I know. So my question is what's the unit of the world coordinate system of one 3D model if I don't have GPS/georeference information? Does the world coordinate system is related image pixel? If so, what's the converter factor between those two.

And also when I export the camera information, is the XYZ values are for the principal points or focal points?

Thanks in advance,
Nan