Ground Control

Ground control forms the reference cornerstone for virtually all data collection activities. OTH Geomatics deploys levels, totalstation and RTK GPS in the collection of control points referenced to first and second-order control.

For airborne lidar, we meet or exceed NDEP guidelines for the collection of ground control for digital elevation data as adopted by USGS-NGP-Draft13, even when delivering data outside the U.S. This protocol includes the collection of 20-30 checkpoints across up to 7 major land cover categories representative of the area. As each checkpoint must be visible in the dataset, it is not uncommon to collect several hundred individual GCPs for a project.

For terrestrial mobile lidar, a combination of primary control (base station), secondary control (route pegs) and supplemental Ground Control Points are generally used. However, the exact ground control methodology varies - depending on required accuracy and the actual project conditions encountered. Factors that degrade GPS lock such as tree canopy and urban canyon effects as well as the overall performance of the system during the time of deployment all have an impact on the chosen method and the number of GCPs that are established along the route.