Ground control points (or GCPs for short) consist of a system of points for a given project area whose x, y, and z positions are known and referenced to a ground coordinate system, such as the North American Datum of 1983 (NAD 83), and whose images can be positively identified in corresponding imagery. Historically, such control was established by means of field surveys, until now. CompassData has a proven technology to provide extracted GCPs from remote sensing surveys, eliminating the need to have feet on the ground. Mr. Hayden Howard, Vice President at CompassData commented that “until recently, there has been no option for controlling an optical image in restricted areas such as China, Cuba and North Korea but with this technology we are now able to extract accurate coordinates for features that can be used to verify or control a satellite image or DEM.” CompassData’s technique has great advantages in remote and dangerous terrain. CompassData remotely sensed GCP (RSGSP) technique involves the extraction of accurate 3D RSGCPs from TerraSAR-X SpotLight and StripMap images.
They have evaluated the RSGCPs against Differential GPS control points and/or a highly accurate LiDAR DEM on varied test sites, all situated in challenging terrain and confirm accuracies to +/- <1m. Such control is ready for use in accurate georeferencing of airborne and spaceborne imagery and for the vertical and horizontal assessment of digital elevation data, to name two common applications of GCPs. Although GCPs collected by terrestrial means typically offer higher accuracies, this spaceborne approach is a significant milestone in control.