Point-Based Graphics

Point-based geometry representations allow to process and visualize 3D models without the need for costly surface reconstruction or triangulation. They are therefore a flexible and efficient alternative to traditional spline-based or mesh-based surface representations [3]. For instance, point-based representations allow for simple and efficient level-of-detail rendering and progressive transmission [1].

**Figure 1:** Point-based rendering allows for easy and efficient level-of-detail rendering, since no mesh connecticity has to be updated. The image shows progressive transmission of the David model with 5%, 15%, 50%, and 100% of the data [1].

A crucial component for any interactive application using point-based representation is the visualization. Due to the lack of hardware support for point primitives, early point-based rendering techniques were pure software implementations [1], and hence were too slow for real-time visualization of highly complex data sets. However, the increasing programmability of current graphics hardware (GPU) allows for hardware-accelerated point rendering [2,4], using so-called surface splatting, where each point sample is equipped with a normal vector and a radius, and therefore represents a small circle or ellipse in object space.

**Figure 2:** A model that representated by elliptical splats (left), rendered using flat shading (center left), Gouraud shading (center right), and Phong shading (right) [5].

High visual quality is and flexible rendering is achieved using multi-pass deferred shading achieved by the inherent anti-aliasing of surface splatting, as well as by per-pixel Phong shading and shadow mapping [5,6]. A systematic description of several rendering approaches is given in the book [8].

**Figure 3:** Phong shading can be implemented efficiently using deferred shading, based on the depicted three rendering passes [6].

**Figure 4:** Using a deferred shading framework, other shading modes, such as the depicted non-photorealistic rendering and shadow mapping, can be implemented easily and efficiently [6].

The point-based rendering metaphor, where elliptical splats are generated from simple OpenGL points, has also been successfully applied in scientific visualization. For instance, in molecular visualization, individual atoms and their connections can be represented by sphere and cylinders, respectively, which are generated and rasterized completely on the GPU [7]. Thanks to the high rendering performance, even dynamic (pre-computed) MD simulations of large membrane patches can be visualized in realtime, which we exploited for an interactive “atom-level magnifier tool” in a combined mesoscopic and molecular visualization [9].

**Figure 5:** The principles of point-based rendering carry over to molecule visualization, by rasterizing spheres, ellipsoids, and cylinders on the GPU [7].

**Figure 6:** Point-based molecule rendering allows for interactive magnifier tool that bridges the gap between cell visualization of the mesoscopic (left) and molecular scale (right) [9].

[1]	Efficient high quality rendering of point sampled geometry Mario Botsch, Andreas Wiratanaya, Leif Kobbelt Eurographics Workshop on Rendering 2002, pp. 53-64. Paper
[2]	High-Quality Point-Based Rendering on Modern GPUs Mario Botsch, Leif Kobbelt Pacific Graphics 2003, pp. 335-343. Paper
[3]	Phong Splatting Mario Botsch, Michael Spernat, Leif Kobbelt Eurographics Symp. on Point-Based Graphics 2004, pp. 25-32. Paper
[4]	A Survey of Point-Based Techniques in Computer Graphics Leif Kobbelt, Mario Botsch Computers & Graphics 28(6), 2004, pp. 801-814. Paper
[5]	Perspective Accurate Splatting M. Zwicker, J. Räsänen, M. Botsch, C. Dachsbacher, M. Pauly Graphics Interface 2004, pp. 247-254. Paper
[6]	High-Quality Surface Splatting on Today's GPUs Mario Botsch, Alexander Hornung, Matthias Zwicker, Leif Kobbelt Eurographics Symp. on Point-Based Graphics 2005, pp. 17-24. Paper Presentation
[7]	GPU-Based Ray-Casting of Quadratic Surfaces Christian Sigg, Tim Weyrich, Mario Botsch, Markus Gross Eurographics Symp. on Point-Based Graphics 2006, pp. 59-65. Paper Video Erratum
[8]	GPU Splatting Mario Botsch, Leif Kobbelt Chapter in Point Based Graphics, Markus Gross, Hanspeter Pfister (Editors) Elsevier / Morgan Kaufmann, ISBN 0123706041, 2007.
[9]	Membrane Mapping: Combining Mesoscopic and Molecular Cell Visualization Thomas Waltemate, Björn Sommer, Mario Botsch Proceedings of Eurographics Workshop on Visual Computing for Biology and Medicine, 2014, pp. 89-96. Paper Video

Point-Based Graphics

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