A stand guidance system, Visual Docking Guidance System (VDGS) or Advanced Visual Docking Guidance System (A-VDGS) is a system that assists pilots to park an aircraft in an airport stand.
Most large international airports have already installed A-VDGS systems in most of their airport stands. These systems are largely aimed at replacing airport marshalls. Although airport marshalls are now being replaced by VDGS systems, small airports still use marshalls regularly to guide aircraft into the gate.
VDGS
VDGS systems usually consist of an Azimuth Guidance for Nose-in Stands (AGNIS) along with Parallax Aircraft Parking Aid (PAPA).
The light bars on the AGNIS display one of the following signals:
- There are two bars
- If both are green, they indicate correct alignment
- If one is red, they need to steer away from the side that has turned green
Credit: Wikimedia
A-VDGS
ADVGS systems use more sophisticated electronic systems to determine the location of the aircraft and use electronic screens to better inform and assist the pilot.
There are a variety of stand guidance systems that are categorized as AVDGS. Here are some of the examples:
RLG
The RLG GIS-206 is an AVDGS system that uses lasers to determine the position of the aircraft, subsequently displaying the distance the aircraft must go as well as showing an Azimuth guidance.
The top screen displays the aircraft type, the second displays the distance in meters and in the bottom left, there is a Azimuth guidance system. (Pilots are supposed to move away from the red side)
APIS by FMT
The Aircraft Positioning and Information System is an AVDGS system that utilizes lasers to guide the aircraft in. The laser calculates the distance it needs to stop, which it displays on the bottom right screen.
Additionally, the APIS uses an azimuth guidance that is based on the Moire Pattern. Learn more about the Inogon marker (the bottom left) in this article here.
By Nicholas.innigo.evans – Own work, CC BY-SA 3.0 
By Nicholas.innigo.evans – Own work, CC BY-SA 3.0 
By Nicholas.innigo.evans – Own work, CC BY-SA 3.0
Safedock by ADB Safegate
ADB Safegate’s Safedock line has multiple A-DVGS stand guidance products. Here are some examples of Safedock products.
Safedock T-Series
Safedock T1
Image Credit: ADB Safegate
Safedock T2
Image Credit: ADB Safegate
Safedock T3
Image Credit: ADB Safegate
Safedock X
The Safedock X is a new series of A-VDGS systems that includes integration with Advanced Surface Movement Guidance and Control System (A-SMGCS).
Credit: ADB Safegate 
Credit: ADB Safegate