In late 2021 and early 2022, Baseline | DCCM performed accurate horizontal and vertical GPS control surveying to update the existing City of League City GPS Survey Control Monument System. The existing 36 control monuments were recovered and reobserved, and observed or missing monuments were reset. Multiple redundant RTK GPS observations using the Hexagon (Leica) HxGN SmartNET Real-Time Network were performed on each point, using a minimum of three different satellite constellations were performed on each point.

The disturbed and missing points were reset with ¾-inch aluminum, deep sectional rods in 6-inch PVC sleeves in concrete. The rods were driven to refusal or a maximum depth of 27 feet.

Steel access covers marked the League City survey control point, and point designation (point number/identifier) was installed on each new point. The updated and new data obtained on each existing and new point consisted of the following:

• Horizontal datum: NAD 83, CORS adjustment (2011), EPOCH 2010.00 in U.S. survey feet Texas Coordinate System, South Central Zone 4204. North and east coordinates were reported in grid values and latitude/longitude. Mapping angle, scale factor, and combined scale factor were also provided.
• Vertical datum: NAVD 88 CORS adjustment with GEOID Model 18. Elevations were reported in U.S. survey feet.

A detailed survey report was provided, which included:

• Detailed summary with background information (monument history) and survey methodology used
• Overall project vicinity maps showing the location of points
• SmarNet CORS information sheets
• Final coordinate list
• New survey control data sheets