The technique hinges upon the use of a set of numbered controls that 1) appear in the structure from motion point cloud model and 2) are mapped by a survey instrument (high accuracy GPS or accurately coordinated total station). Using the Helmert transformation, the arbitrary coordinates of the modeled targets are transformed into the real world coordinate system of the mapped reference targets. With the exception of Microsoft Excel (which could probably be replaced by OpenOffice), the entire work flow employs free software.