A Visual Docking Guidance System is a system used to assist aircraft to dock at the exact position in front of respective gates.
Stand Guidance System - A Stand Guidance System is a system responsible for providing information to the pilot, when attempting to park an aircraft at an airport stand. The information is largely visual, and enables the aircraft to avoid potential obstructions.
Stand Entry Guidance System - Stand Entry Guidance (SEG) Systems have the same function as Stand Guidance Systems. They provide information to flight personnel and allow for precise parking at airport gates. Modern systems are capable of identifying the type of aircraft attempting to park, and alert the pilot that the guidance will be type-specific. Warnings are issued in case of an error, such as the aircraft going off track or entering the stand too fast.
Centerline and Docking Compliance Data - Centerline and Docking Compliance Data falls under the bracket of crucial aviation-oriented data that can be used to improve turnaround time. During docking and taxiing, pilots follow a centerline in order to avoid collisions with infrastructure, aircrafts, etc. The aircraft is also required to stop at the correct places, as aforementioned, following which they are assisted further by VDGS. Centerline and Docking compliance data provides pilots and flight crew with updates about how accurately the aircraft is following the apron markings.
This data is needed primarily for purposes of safety, and to monitor any violations in the docking process.
Advanced Visual Docking Guidance System - Advanced Visual Docking Guidance Systems or A-VDGS are the updated versions of VGDS, wherein a parking position for docking can be enabled with a maximum deviation of 10 cm. The advanced system is more precise, and allows the the boarding bridge for passengers to be aligned very closely with the final position. When it is time for docking, movements are limited to a minimum.