Keyboard shortcuts for pop-out interactive viewer

A minimal pop-up interactive viewer can be created by running .view() on any Image, Dose, ROI or StructureSet from python outside of a Jupyter notebook. The controls are:

• scroll: move 1 slice

• left/right keys: move 1 slice

• up/down keys: move 5 slices

• v: toggle orientation between axial, sagittal, and coronal

• d: toggle dose field opacity (if viewing dose field overlaid on image)

• c: toggle ROI plotting type between contour, filled, and mask (if viewing ROIs)

• j: jump between ROIs (if viewing a StructureSet)