Control imports define the project’s coordinate system - so in this way they are like a multi-point transform, but they also affect the processing. Control points are carried in the optimization and can modify the shape of the 3D model. They can help solve single photo projects and projects with weak camera geometry. The project adjusts to match the positions of the marked control points, for example when taking points from a survey and using them to orient a project in the same coordinate system.
Control points are also used when solving for unknown cameras using Inverse Camera features (see Inverse Camera solves for).
To 'control' a project in this way, you will typically assign the imported point coordinates to existing 3D points in your model. PhotoModeler will use these imported coordinates to modify the model to fit the points to these positions. Control points are used for Single Photo Projects, for Inverse Camera projects, and for camera Orientation if model data is weak.