The classic perspective projection is mostly used when calibrating a camera. Although this approach is fairly developed and often suitable, it is not necessarily adequate to model any camera system like fish-eyes or catadioptrics. The perspective projection is not applicable when field of views reach 180° and beyond. In this case an appropriate model for a particular non perspective camera has to be used. Having an unknown camera system a generic camera model is required. This paper discusses a variety of parametric and generic camera models. These models will be validated subsequently using different camera systems. A unified approach of deriving initial parameter guesses for subsequent parameter optimisation is presented. Experimental results prove that generic camera models perform as accurate as a particular parametric model would do. Furthermore, there is no previous knowledge about the camera system needed.