The GPU allows for data from an avionics source to be converted into a typical HUD display format. The GPU is connected to aircraft avionics systems via Arinc-429 databus and/or RS-232 Serial channel(s). For full functionality the GPU requires Air Data and Heading Reference data (ADAHRS) along with GPS navigation data. Internal to the GPU, software converts data to graphics.
See the video below of HUD display graphics. Members of Epic Optix team have been both military and commercial pilots. As a result of those experiences, we have created what we consider to be the best of HUD displays to develop this simple output.