This tutorial shows how to use Geogebra to construct the canonical coordinate system for a particular configuration of a four-bar linkage.
It starts with a quadrilateral which is to be the configuration of the linkage at a particular instant. Then constructs the velocity pole and the instant center of the positions of the input and output cranks. Connecting these lines defines the collineation axis.
Bobillier’s theorem completes the construction by defining the tangent to the moving centrode.