This system adopt automatically monitor method to monitor the dam surface displacement monitoring, the principle is: Each monitor station get the real-time GNSS data from the reference station, then through the network send the result to the control center, HC Monitor software will calculate the real differential data and list the 3D coordinates with the monitor station, check with the initial coordinates, through the analyze software to get the alarm service. 
GNSS surface displacement monitoring’s horizontal accuracy: ±2mm+1ppm,vertical accuracy: ±4mm+1ppm. 
Note: GNSS surface displacement point can calculate with local coordinate system, all monitor point coordinates can convert to local coordinates.