A known point measured or surveyed on the ground (opposed to a camera station position that could be anywhere in 3D space). These points are often provided by a surveyor and used in UAS projects to tie the project into a known coordinate system or known geographic coordinate system. A control point in PhotoModeler modifies the optimization and can improve (or degrade) accuracy and calibration. Compare to a multi-point transform point which is also external data but does not modify processing – it is used to fit a project, post processing, into a coordinate system without warping.