The High Definition Geomagnetic Model (HDGM) is a global, high resolution model (degree 720) of the Earth's geomagnetic main and crustal field, providing magnetic field values (total field, dip, and declination) at any point above or below the Earth's surface. An optional addition to HDGM is the HDGM-RT, which includes a model of Earth's magnetosphere which provides near real-time estimates of the external disturbance field due to the solar wind. It also contains a magnetic field model of the daily variations due to the ionospheric current systems.