This paper describes a method for online interactive building of piecewise planar environments for immediate use in augmented reality. This system combines user interaction from a camera-mouse and automated tracking / reconstruction methods to recover planar structures of the scene that are relevant for the augmentation task. An important contribution of our algorithm is that the process of tracking and reconstructing planar structures is decomposed into three steps - tracking, computation of the intersection lines of the planes, reconstruction - that can each be visually assessed by the user, making the interactive modeling procedure really robust and accurate with intuitive interaction. Videos illustrating our system both on synthetic and long real-size experiments are available at http://www.loria.fr/~gsimon/vc