1. A non-transitory computer-readable storage medium storing instructions for marking a main carina and a trachea of a patient, the instructions, when executed by a processor, cause a computing device to: import slice images of a chest of a patient from an imaging device; generate a three-dimensional (3D) model based on the imported slice images; display the 3D model in a graphical user interface (GUI); display, via the GUI, two-dimensional (2D) images of the 3D model; receive a selection of the main carina in one of the 2D images of the 3D model; mark the main carina in one of the 2D images of the 3D model; adjust a view plane of the 3D model around a rotation axis defined by the marked location of the main carina to adjust the view plane from an axial orientation to a coronal orientation while keeping the main carina in the view plane to thereby display the entire trachea in the GUI; receive a selection of an upper end of the trachea in one of the 2D images of the 3D model; and mark the upper end of the trachea in one of the 2D images of the 3D model.