Electromagnetic Radiation from the Geometrical Point of View

The article describes the relationship between the solutions of Maxwell's equations which can be considered at least locally as plane waves and the curvilinear coordinates of geometrical optics. We introduce phase-ray coordinate system for any electromagnetic field if vectors E and H are orthogonal to each other and their directions do not change with time t, but may vary from point to point in the domain G. © The Authors, published by EDP Sciences, 2018.