Carl Erikson

View-dependent simplification of arbitrary polygonal environments

This dissertation describes hierarchical dynamic simplification (HDS), a new approach to the problem of simplifying arbitrary polygonal environments. HDS is dynamic, retessellating the scene continually as the users viewing position shifts, and global, processing the entire database without first decomposing the environment into individual objects. The resulting system enables real-time display of very complex polygonal CAD models consisting of thousands of parts and millions of polygons. HDS supports various preprocessing algorithms and various run-time criteria, providing a general framework for dynamic view-dependent simplification. Briefly, HDS works by clustering vertices together in a hierarchical fashion. The simplification process continually queries this hierarchy to generate a scene containing only those polygons that are important from the current viewpoint. When the volume of space associated with a vertex cluster occupies less than a user-specified amount of the screen, all vertices within that cluster are collapsed together and degenerate polygons filtered out. HDS maintains an active list of visible polygons for rendering. Since frame-to-frame movements typically involve small changes in viewpoint, and therefore modify this list by only a few polygons, the method takes advantage of temporal coherence for greater speed.

MMR: an interactive massive model rendering system using geometric and image-based acceleration

We present a system for rendering very complex 3D models at interactive rates. We select a subset of the model as preferred viewpoints and partition the space into virtual cells. Each cell contains near geometry, rendered using levels of detail and visibility culling, and far geometry, rendered as a textured depth mesh. Our system automatically balances the screen-space errors resulting from geometric simplification with those from textureddepth-mesh distortion. We describe our prefetching and data management schemes, both crucial for models significantly larger than available system memory. We have successfully used our system to accelerate walkthroughs of a 13 million triangle model of a large coal-fired power plant and of a 1.7 million triangle architectural model. We demonstrate the walkthrough of a 1.3 GB power plant model with a 140 MB cache footprint.

HLODs for faster display of large static and dynamic environments

We present an algorithm and a system for accelerated display of massive static and dynamic environments using hierarchical simplification. Given a geometric dataset, we represent it using a scene graph and compute levels of detail (LODs) for each node in the graph. We augment the LODs with automatically-generated hierarchical levels of detail (HLODs) that serve as higher fidelity drastic simplifications of entire branches of the scene graph. We extend the algorithm to handle a class of dynamic environments by incrementally recomputing a subset of the HLODs on the fly when objects move. We leverage the properties of the HLOD scene graph in our system, using them to render the environment in a specified image quality or target frame rate mode. The resulting algorithms have been implemented as part of a system named SHAPE. We demonstrate its performance on complex CAD environments composed of tens of millions of polygons. Overall, SHAPE is able to achieve considerable speedups in frame rate with little loss in image quality.

GAPS: general and automatic polygonal simplification

We present a new approach for simplifying polygonal objects. Our method is general in that it accepts models that contain both non-manifold geometry and surface attributes. It is automatic since it requires no user input to execute and returns approximate error bounds used to calculate switching distances between levels of detail, or LODs. Our algorithm, called General and Automatic Polygonal Simplification, or GAPS for short, uses an adaptive distance threshold and surface area preservation along with a quadric error metr ic to join unconnected regions of an object. Its name comes from this ability to “fill in the gaps” of an object. Our algorithm combines approximations of geometric and surface attribute error to produce a unified object space error metric. GAPS can efficiently produce high quality and drastic approximations of a wide variety of objects, including complicated pipe structures. This ability to perform drastic simplification allows us to create levels of detail to accelerate the rendering of large polygonal environments, consisting of hundreds of objects. When viewing these models with LODs created by GAPS, we achieve a 3.5 to 5 times average speedup with little loss in image quality.