1. Types of measures

Although there are many different models of terrestrial laser scanners, the basic operating principle is the same for all of them:

• a motor for controlled rotation around the instrument's main axis (usually almost vertical);

• in parallel, a system of mirrors or prisms rotates about an axis perpendicular to the first ;

• a laser pump emits a beam which, using different techniques, provides distance information;

• we'll also store the intensity of the return signal.

It is possible to determine the three-dimensional position of the impact of the emitted beam in a reference frame local to the scanner position with the polar information shown in figure