This report describes the design and implementation of a controller that guides a ground vehicle from its current position to a predefined target. The controller is part of an Application Program Interface, API, together with lower level functions for controlling individual actuators and obtaining data from sensors, and some other, middle level controllers for various purposes. These functions are all accessible from applications based on various algorithms with the purpose of exhibiting autonomous behaviour. This particular controller observes position, velocity and course based on information obtained from a satellite navigation sensor, a GPS receiver. It uses other functions to control speed and steering on the platform, currently based on an electrically driven Radio-controlled car, about 0.5 m long. The controllers are executed on a one chip computer, PC-104 standard, Pentium-class PC running the Debian GNU/Linux operating system.