Fig. 3
From: A novel method for robust markerless tracking of rodent paws in 3D
This figure shows the concept for 3D reconstruction using two cameras image planes (focal planes of cameras). O is a point located in a 3D object space having the X, Y, and Z coordinate system. I1 and I2 are the projected points in the image plane 1 of camera 1 and the image plane 2 of camera 2, respectively