When rendering a new frame using a hybrid ray tracing process, a graphics processor transforms vertex position data for models representing objects in the new frame into camera space for use in a rasterisation process of the hybrid ray tracing process irrespective of whether the object has moved between frames or whether the geometry of the model representing object has changed, but only transforms vertex position data for a model for an object into world space for use in a ray tracing process of the hybrid ray tracing process when the object has moved between frames or where the geometry of the model representing the object has changed.