Instructions provided describe how to set ground control points (GCPs). GCPs are fixed features visible in Site Scan for ArcGIS source images, with accurate and precise, known positions. They are used to enhance the absolute accuracy of Site Scan outputs.
Without GCPs, Site Scan outputs are solely georeferenced using the drone’s GNSS receiver and inertial sensors. While the relative accuracy within the models is high, the absolute accuracy, or where the model is located on Earth, may shift between 2-8 feet.
Setting ground control points
Number of GCPs and layout
A minimum of three points is required. For optimal results, a minimum of five control points is recommended for a site of any size.
To maintain high accuracy throughout the processed outputs, Esri recommends using additional points for large or oddly shaped sites, or sites with many elevation changes.
For sites wider than 20 acres (eight hectares), Esri recommends adding one GCP for each subsequent 15 acres (six hectares).
To set the first five points, visualize the five faces of a dice. One point near each corner, but not on the very edge of the mapped area, and one near the center. Distribute other points evenly between the first five.
Sample GCP layouts
Active construction sites may have difficulty laying a control point near the center of the site, and it is acceptable to omit this point if unpractical. Esri recommends adding at least two additional points along the perimeter.
Measuring GCP position