# Real Time Shadow Mapping for Augmented Reality Photorealistic Rendering
## 2 State of the Art  
To ensure a realistic experience in AR and Virtual Reality (VR), several requirements must be met, for example a correct and stable pose of the objects with respect to the user's view, an intuitive interaction with the holograms and a high frame rate to ensure fluidity to the stream. In recent years, most research has been done to improve tracking system for AR applications [2; 3; 4] and also the calculating power of AR devices has increased. Due to these achievements, visual quality of the augmented objects began to gain importance in the realism of the AR simulations: in fact, even if the augmented 3D models are posed with extreme precision and tracked with high frame rate, their visual quality reveals they are artificial. This happens because the simulation of environment lighting is poor and weak. There are of course many cases where this realism is not necessary, but could make the job more immersive [5; 6]. In VR applications, the principal requirement is the sense of presence, the power for the graphics user believe he is in an environment that does not exist. Lighting has the big task of making that happen. Instead, for AR application, lighting has the task of seamlessly inserting synthetic model in the scene. To do this, virtual lighting of 3D objects has to match the lighting of the surrounding environment in order to create the illusion of real objects. Moreover, this process must be as rapid and automated as possible, in order to be performed by not skilled users and to ensure a high frame rate. Available techniques for realistic real-time rendering of objects are usually characterized by long setting time and they are not always successful. Generally, the set-up is manually made and pre-calculated. This way, the position, color and intensity of virtual light sources are different in any environment and an automated standalone application cannot be used. Another technique consists in using a photo of a reference object, for example a grey sphere, previously taken in the environment, and use its appearance to manually set up the lightning conditions. Nevertheless, the problem of manually configuring the lightning environment remains. [PERSON] [7] firstly proposed to use a set of photographs of a reflective sphere with different exposures in order to reconstruct the lighting scheme of the environment. This method has effective results but requires a physical support and a great computational effort, not suitable for real-time rendering. In [8], the authors proposed a real-time lighting acquisition procedure that computes the lights pose using a diffuse sphere, a ping pong ball, and it is rapid enough to guarantee real-time renderings. However, this method also requires a physical support. In [9], the authors developed a pipeline for rendering and lighting augmented objects over planar surfaces. The process does not manage environment lighting changes, thus it is not suitable for real-time application. In [10], the authors proposed the use of HDR images to deduce environment radiance values and to project them onto a 3D geometry reconstruction of surrounding environment. This process is totally probeless, since is based on HDR images but requires a server-client data exchange. Moreover, the environment geometry and objects materials of the scene are manually reconstructed, thus this process is tedious and time-consuming. In addition, in [11], the authors proposed the use of a probe in order to reconstruct the environment map and estimate light source direction as well as focused on the algorithm of shadows creation. Our method instead is probeless, as mentioned above, and we did not concentrate on the shadow creation algorithm, because we rely on the Unity built-in shadow method, while we faced the problem of creating the shadow onto a transparent screen. Moreover, the proposed method does not require calculating the light source position every frame, but only once at the beginning of the AR session or, if necessary, when the environment lighting scheme is drastically changed.