An Image-space Approach to Interactive Point Cloud Rendering Including Shadows and Transparency

Point-based rendering methods have proven to be effective for the display of large point cloud surface models, basically replacing global surface reconstruction with local surface estimations, for example, via splats or implicit functions. Crucial to their performance in terms of rendering quality and speed is the representation of the local surface patches. We present an approach that avoids any object-space operations and computes high-quality renderings by only applying imagespace operations. The image-space operations apply a pipeline of filters to a point cloud after being projected to image space. Those filtering operations appropriately fill background pixels and occluded pixels and produce visually pleasing results using smoothing and antialiasing. For a realistic visualization of the models, transparency and shadows are essential features. We propose a method for point cloud rendering with transparency and shadows at interactive rates. Again, all passes are executed in image space and no pre-computation steps are required. The underlying technique for our approach is a depth peeling method for point cloud surface representations. Having detected a sorted sequence of surface layers, they can be blended front to back with given opacity values to obtain renderings with transparency. These computation steps achieve interactive frame rates. For renderings with shadows, we determine a point cloud shadow texture that stores for each point of a point cloud whether it is lit by a given light source. The extraction of the layer of lit points is obtained using the depth peeling technique, again. For the shadow texture computation, we also apply a Monte-Carlo integration method to approximate light from an area light source, leading to soft shadows. Shadow computations for point light sources are executed at interactive frame rates. Shadow computations for area light sources are performed at interactive or near-interactive frame rates depending on the approximation