The objective of our paper is to describe a method to determine the scanning strategy for a CAD known mechanical part by using a plane laser sensor. The Research Centre for Automatic control in Nancy (France) has initiated a project to create an automatic 3D digitising system. Our previous papers focused on the visibility determinations using spherical geometry in a 3 axis environment. This communication is dedicated to our path planning method, including the collision avoidance. The different algorithms presented were developed for a 5 degrees of freedom (DOF) but due to our digitising environment, we applied them to a 3 axis scanning cell that is composed of a plane laser sensor integrated onto a CMM by means of a mechanical system. Compared to a 5 axis system, we have to search the association between each indexed position and some parts of the piece that will be digitised from the sensor position. For each step of our methodology, we will illustrate algorithms by a case study.