Control Points
The Surveys tab allows you to edit or display the survey data attached to a block: Survey points and positioning constraints.
Control points are registered in 2D-images and correspond to a same physical point with known 3D-coordinate.
Control points can be added manually or can be imported from a columned file. See also Importing control points.
Usage
Adding control points to a block enables accurate geo-referencing and avoids long-range metric distortion.
A set of control points can be used by aerotriangulation if it consists of 3 or more control points, each of them with 2 or more image measurements.
See also Aerotriangulation.
Adding a control point
- Click on Add Survey Point.
- Define Name.
In the Survey Point dialog, select Type “Control Point”.
- Enter 3D Coordinates
Select the input coordinate system in the combo-box, and the known 3D coordinates.
"Local coordinate system" system can be used to enter non-georeferenced control points with arbitrary units or with known units.
- Click on Create
The new Control point appears in the list.
- You can set additional control point options (category, accuracy, check point, etc.) from the item properties (page 62).
- Place the survey point on
photos.
Select a photo displaying the survey point, define its position in the photo with the yellow marker and click Accept position (alternatively, use Shift+Click to set directly the position on the photo).
Repeat the sequence of operations above to set the position in several photos.