North Central Texas Council of Government

Ellis and Henderson Counties, Texas

G&AI performed survey services for the 2017 NCTCOG orthoimagery and LiDAR project. The project required 116 ortho imagery PID points to support ASPRS Class I accuracy orthoimagery within the 13,866 square miles orthoimagery project area, 56 LiDAR control points, and 33 LiDAR checkpoints to support ASPRS Class I accuracy LiDAR data within the 1340 square mile LiDAR project area. Total points surveyed were 205 and all survey met the project accuracy specifications. The ground control accuracy satisfied a Local Network accuracy of 5-centimeters at the 95% confidence level.

Additionally, in 2015 G&AI provided ground control for the NCTCOG 0.5m aerial LiDAR project for TRWD, totaling 618 square miles. Scott Dunham (G&AI’s Lidar Services Technical Director) served as the prime firm’s project manager on this project prior to joining our firm. All LiDAR conformed to USGS v.1 specifications (NPS ≤ 0.500 m, or point density ≥ 4 points per m²) for first-return data. G&AI field crews collected the ground control and QA/QC check points using GPS-based real-time kinematic (RTK) survey techniques. For the RTK survey, the field crew used a roving unit to receive radio-relayed corrected positional coordinates for all ground points from a GPS base unit set up over survey control monuments. The roving unit recorded precise location measurements with an error of ≤ 1.5 cm (0.6 in). G&AI distributed the RTK ground checkpoints (GCPs) throughout the task order AOI.

This project was delivered on time and exceeded accuracy specifications.