1. A method for determining the pose of a camera with respect to at least one object of a real environment for use in an authoring or augmented reality application, comprising: generating a first image comprising at least one image by a camera capturing a real object of a real environment; generating first orientation data describing a normal to a ground plane within a coordinate system from at least one orientation sensor associated with the camera or from an algorithm which analyses the first image to find and determine features which are indicative of an orientation of the camera; obtaining a virtual reference model within said coordinate system, wherein said virtual reference model represents a known sized object; displaying said virtual reference model superimposed with the real environment at a position in the first image and providing an initial distance from the camera to the virtual reference model; receiving user instructions to manipulate the virtual reference model by a user, then modifying the position or orientation of the virtual reference model resulting in at least a change in the position of the virtual reference model within the real environment, including at least one of moving the position of the virtual reference model within the first image on a plane, with the plane defined at least in part by the first orientation data, zooming the virtual reference model to alter the position, rotating the virtual reference model; calculating a distance of the camera to the real object of the real environment displayed in the first image according to the position of the virtual reference model based on said manipulating of the virtual reference model by the user, and generating distance data that is indicative of the distance; determining a pose of the camera with respect to said coordinate system associated with said virtual reference model and related to the real object of the real environment using the distance data and the first orientation data.