A gnomon is a 3D symbol for an absolute XYZ coordinate system. It provides a reference to understand the orientation of objects in the view. You can create a custom gnomon to provide an additional, graphical reference. Define a gnomon from any model OL (*.ol) file. You can select a gnomon from a library of any number of custom gnomons. The gnomon is not saved to the C3DI (*.c3di) illustration file.