Ground Control Collection

Ground control forms the reference cornerstone for virtually all activities. OTH Geomatics' ground control methodology is specifically tailored for individual mission requirements, and executed using the highest industry standards, referenced to first and second-order control.

Before project kick-off, the requirements and methodology for gathering GCPs are fully delineated and approved by the client. This ensures all project stakeholders are in agreement with regards to overall accuracy requirements, and a general consensus is reached that the GCP strategy is adequate to compensate for accuracy degradations given the projected PDOP and anticipated GPS outage specific to each deployment. This allows potential trouble-spots to be identified early on and GCP sampling frequency adjusted to suit.

We meet or exceed NDEP guidelines for the collection of ground control for digital elevation data as defined by USGS-NGP-Draft13, even for projects outside the U.S. This protocol includes the collection of 20-30 checkpoints across (up to) 7 major land cover categories representative of the study area. As each checkpoint must be visible in the dataset, for airborne lidar each checkpoint is typically comprised of several individual observations. It is not uncommon to collect several hundred individual GCPs for such a project.

Actual survey practices for establishing GPS-derived ellipsoidal heights conform to NOAA NOS NGS-58. This ensures the highest standard ground control product, with checkpoints at least three times more accurate than the elevation datasets being tested.

By adopting this approach, we have found that site re-visits to capture supplemental data are greatly reduced, keeping project schedules on-track.