In one example, a system for real-time three-dimensional (3D) calibration includes a processor detecting mark corners at two-dimensional (2D) coordinates in an image coordinate system of an image of a specified pattern. The processor determines 3D coordinates of the mark corners in a world coordinate system based on the pattern. The 3D coordinates correspond to the 2D coordinates. The processor determines baseline depth values corresponding to original depth values for proper points on a mark plane, based on the 2D coordinates and the 3D coordinates. The processor generates a fitting model based on the baseline depth values.