About Control Points
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.
When a control point is added, a control point symbol is displayed in the 3D Window in the place where it was added. When selected, the control point turns to purple.
Control Point Symbol
Do any of the following:
§ Create control points:
§ Mark a control point in photos
§ Export control point data to a tab delimited .gcp (text format) file
§ Import control point data in a tab delimited .gcp (text format) file
§ Use control point as a check point to sample the AT accuracy in the result
The capabilities listed above (except for the export of control point data) are available from the Control Point contextual tab and also from the control point shortcut menu. See “Control Point Menu” in the “Using the Project Tree and Item List” chapter for more information. Control point data is exported from the Control Points command on the Home tab.