This purpose for this external geometry is to establish or modify the coordinate system of your 3D model, which involves translation, scale and rotation or some combination of these.
To define a coordinate system transformation in this way you will typically assign the imported point coordinates (or scales) to existing 3D points in your model. PhotoModeler will do its best to fit the model to the coordinates of the known external geometry data.
Defining the coordinate system differs from Control the Solution in that the assignment of the coordinates will transform the model without changing the shape of, nor warping the model. Using control points will modify the model based on the 3D positions of the control points. As well control points are used during, and affect processing – here they do not.