GPS Control Network Surveys
LJA Engineering has been utilizing Global Positioning System (GPS) equipment to establish high order horizontal and vertical control since 1999. All work is performed in accordance with Geometric Geodetic Accuracy Standards and Specifications for Using GPS Relative Positioning Techniques as established by the Federal Geodetic Control Sub-Committee (FGCS), August 1989. All work to establish vertical elevations or benchmarks is performed in accordance with guidelines and procedures established by the National Geodetic Survey (NGS) as outlined in NOAA Technical Memorandum NOS NGS-58, Guidelines for Establishing GPS-Derived Ellipsoid Heights, Version 4.3.
LJA Engineering uses Trimble R8 dual frequency receivers capable of both static, fast static and real time kinematic (RTK) observation modes. Data is processed using Trimble Geomatic Office software along with Star*Net least squares adjustment software. To verify survey results, elevations are checked by running conventional level loops between known control points using a Leica NA3003 or Trimble DiNi digital level with bar coded level rod and turning shoe in accordance with FGCS standards and procedures.
In May of 2000, LJA Engineering established two A-Order primary control monuments to serve as the basis for the future development of a countywide benchmark network. Material and construction for the monuments were installed in accordance with the NGS guidelines. Company personnel worked closely with NGS to “blue book” these two monuments which are listed as Texas Height Modernization monuments.
These same rigid procedures are used by LJA Engineering field crews routinely in establishing horizontal and vertical control benchmarks for other projects such as the Washington Blvd. Street and Drainage Rehabilitation Project for the City of Beaumont in 2007 and numerous aerial mapping projects for the Texas Department of Transportation.
LJA Engineering installed a Trimble NetR5 Reference Station with Zephyr antenna as part of the Western Data Systems Texas RTK Virtual Reference System Network. This enables the rapid acquisition of accurate real world coordinates by one man field crews at a reduced cost.