Surveyors use Global Positioning System (GPS) technology to measure the precise location and elevation of points on Earth. In a recent survey, GPS receivers were used to determine the coordinates and elevations of two park monuments. The process involved careful mission planning, data collection, and correction to ensure accuracy. 

The survey began with mission planning to identify optimal satellite visibility and minimize Position Dilution of Precision (PDOP). A geodetic control point served as the base station, where a GPS receiver was set up and the antenna height recorded. Rover GPS receivers were placed above the monument markers, with obstructions cleared for clear satellite views. Data was collected at each site for 30 minutes using the static GPS method to ensure precision. PDOP values were monitored to maintain data quality.  

GPS data was recorded in the Earth-centered, Earth-fixed (ECEF) Cartesian coordinate system. This global system defines positions relative to Earth’s center of mass, ensuring compatibility with geodetic models. The ECEF coordinates are refined using correction software to eliminate ionospheric delays and multipath errors. The corrected coordinates were then converted into latitude, longitude, and ellipsoidal height, with geoid models applied for accurate elevations. Results were validated against control point data, with an accuracy of within 2 centimeters for horizontal positioning and 3 centimeters for elevation, ensuring reliable monument locations and heights.