PhotoMesh provides three types of control points:
- Ground control points (GCP) – Improve the accuracy of the model’s position by associating real-world X, Y, Z coordinates (generally obtained through surveying or sampling methods) with corresponding locations (in pixels) in photos. In order to enable your control points to be fully utilized in the AT process, it is recommended to add at least 3-5 control points per AT tile. When only two control points are provided, simple vertical adjustment, scaling and rotation are performed. When only one control point is provided, only vertical adjustment is performed.
- Check points – Ground control points that do not affect the AT calculation and are only used to sample the AT accuracy in the result. The point is included in the build report and shows calculated errors for accuracy validation purposes.
- Tie points – Establish a correspondence between project photos and improve aerotriangulation results through identification of the same physical point in three or more photos. The XYZ position of the physical point is not necessarily known. Generally, it is recommended to run an initial aerotriangulation to identify photos that either weren’t calculated in AT or that have high median errors, as well as areas of insufficient matches between groups of photos.
Control points are marked in photos using the Control Point Editor. In addition to the ribbon, the Control Point Editor includes a photo viewing window, a photos panel, a control point table, and a sampled photos panel - that gradually becomes populated with photo thumbnails as you mark the control point in photos. The photos panel displays the photos from which to select the photos for marking control points, either as thumbnails or in table format with relevant photo information.
To learn more about using ground control points, click here.