The Surveys tab allows you to edit or display the survey data attached to a block: Survey points and positioning constraints.

Control points can be added manually or can be imported from a columned file. See also Importing control points (on page 60).

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.

1. Click on Add Survey Point.
   
2. Define name.
   

   In the Survey Point dialog, select Type "Control Point".

3. 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.
4. Click on Create. The new Control point appears in the list.
5. You can set additional control point options (category, accuracy, check point, etc.) from the item properties (page 62).
6. 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).
   

   Defining positions on photos

   Repeat the sequence of operations above to set the position in several photos.