What is left film projection center photogrammetry?

The photography center of a photo is the position where the camera focus is at the moment when the photo is taken, that is, the four elements of X, Y, Z, Y and Z are on the outside of the image, and the connecting line between the photography center and the main point is perpendicular to the photo plane. The left film is easy to understand, right? Isn't there a left picture and a right picture for stereo image alignment? That's the photography center of the photo on the left! You can find a book called Photogrammetry, which should contain pictures of the projection principle. Understand at a glance!