Knowledge and Heuristic-Based Modeling of Laser-Scanned Trees, Hui Xu, Nathan Gossett, and Baoquan Chen, ACM Transaction on Graphics, Volume 26, Number 4, October 2007
Abstract
We present a semi-automatic and efficient method for producing full polygonal models of range scanned trees, which are initially represented as sparse point clouds. First, a skeleton of the trunk and main branches of the tree is produced based on the scanned point clouds. Due to the unavoidable incompleteness of the point clouds produced by range scans of trees, steps are taken to synthesize additional branches to produce plausible support for the tree crown. Appropriate dimensions for each branch section are estimated using allometric theory. Using this information, a mesh is produced around the full skeleton. Finally, leaves are positioned, oriented and connected to nearby branches. Our process requires only minimal user interaction, and the full process including scanning and modeling can be completed within minutes.
[DOI]
Sketch-Based Segmentation of Scanned Outdoor Environment Models, Xiaoru Yuan, Hui Xu, Minh x. Nguyen, Amit Shesh, and Baoquan Chen, In Proceedings of the 2nd Eurographics Workshop on Sketch-Based Interfaces and Modeling (SBM'05). Trinity College Dublin, Ireland, Aug 28-29, 2005
Abstract
When modeling with scanned outdoor models, being able to select a subset of the points efficiently that collectively represent an object is an important and fundamental operation. Such segmentation problems have been extensively studied, and simple and efficient solutions exist in two dimensions. However, 3D segmentation, especially that of sparse point models obtained by scanning, remains a challenge because of inherent incompleteness and noise. We present a sketched-based interface that allows segmentation of general 3D point-based models. The user marks object and background regions by placing strokes using a stylus, and the tool segments out the marked object(s). To refine the results, the user simply moves the camera to a different location and repeats the process. Our method is based on graph cuts, a popular and well-tested paradigm for segmentation problems. We employ a two-pass process: we use the strokes to perform 2D image segmentation in the projection plane of the camera and use its results for the 3D scanned data segmentation. The advantages of our method are ease of use, speed and robustness. Our method works for general 3D point models and not just range images. Important applications include selection of objects when dealing with large, unorganized point models for refinement, remodeling, meshing, etc.
[pdf]
PointWorks: Abstraction and Rendering of Sparsely Scanned Outdoor Environments, Hui Xu, Nathan Gossett, and Baoquan Chen, Proceedings of the 2004 Eurographics Symposium on Rendering (EGSR'04). Norrköping, Sweden, Jun 21-23, 2004
Abstract
This paper describes a system, dubbed PointWorks, for rendering three-dimensionally digitized outdoor environments in non-photorealistic rendering styles. The challenge in rendering scanned outdoor environments is accommodating their inaccuracy, incompleteness, and large size to deliver a smooth animation without suggesting the underlying data deficiency. The key method discussed in this paper is employing artistic drawing techniques to illustrate features of varying importance and accuracy. We employ a point-based representation of the scanned environment and operate directly on point-based models for abstraction and rendering. We develop a framework for producing mainly two artistic styles: painterly and profile lines. Strategies have also been employed to leverage modern graphics hardware for achieving interactive rendering of large scenes.
Stylized Rendering of 3D Scanned Real World Environments, Hui Xu and Baoquan Chen, Proceedings of the 3rd International Symposium on Non-Photorealistic Animation and Rendering (NPAR'04). Annecy, France, Jun 7-9, 2004
Abstract
This paper presents an interactive non-photorealistic rendering (NPR) system that stylizes and renders outdoor scenes captured by 3D laser scanning. In order to deal with the large size, complexity and inherent incompleteness of data obtained from outdoor scans, our system represents outdoor scenes using points instead of traditional polygons. Algorithms are then developed to extract, stylize and render features from this point representation. In addition to conveying various NPR styles, our system also promises consistency in animation by maintaining stroke coherence and density. We achieve NPR of large data at interactive rates by designing novel data structures and algorithms as well as leveraging new features of commodity graphics hardware.
Interactive Silhouette Rendering for Point-Based Models, Hui Xu, Minh X. Nguyen, Xiaoru Yuan and Baoquan Chen, Proceedings of the 2004 Eurographics Symposium on Point-Based Graphics (SPBG'04). ETH Zurich, Switzerland, Jun 2-4, 2004
Abstract
We present a new method for rendering silhouettes of point-based models. Due to the lack of connectivity information, most existing polygon-based silhouette generation algorithms cannot be applied to point-based models. Our method not only bypasses this connectivity requirement, but also accommodates point-based models with sparse non-uniform sampling and inaccurate/no normal information. Like conventional point-based rendering, we render a model in two passes. The points are rendered as enlarged opaque disks in the first pass to obtain a visibility mask, while being rendered as regular size splats/disks in the second pass. In this way, edges are automatically depicted at depth discontinuities, usually at the silhouette boundaries. The silhouette color is the disk color used in the first pass rendering. The silhouette thickness can be controlled by changing the disk size difference between two passes.
We demonstrate our method on different types of point-based models from various sources. The simplicity of our method allows it to be easily integrated with other rendering techniques to cater to many applications. Our method is capable of rendering large scenes of millions of points at interactive rates using modern graphics hardware.
INSPIRE: An Interactive Image Assisted Non-Photorealistic Rendering System, M. Nguyen, H. Xu, X. Yuan and B. Chen, , Proceedings of Pacific Conference on Computer Graphics and Applications (PG'03). Canmore, Canada, Oct 8-10, 2003
Abstract
We present a GPU supported interactive non-photorealistic rendering system, INSPIRE, which performs feature extraction in both image space (on intermediately rendered images) and object space (on models of various representations, e.g., point, polygon, or hybrid models) without the need of connectivity information. INSPIRE offers interactive non-photorealistic rendering with most styles that are in the existing NPR systems, and provides more flexibility on model representations.
[pdf] 2.92MB
ActivePoints: Acquisition, Processing and Navigation of Large Outdoor Environments, Hui Xu and Baoquan Chen, Technical Report, University of Minnesota TR.03.02, 2003
Abstract
We describe a system, dubbed ActivePoints (now known as PointWorks), for acquiring large outdoor environments by employing a long-range 3D scanner: Riegl's LMS Z-360 3D image sensor. We have designed and developed algorithms and rendering tools to create efficient 3D representations for scanned data and render the data in real-time. Although ActivePoints shares a common scanning pipeline with most existing scanning systems, it has the following new features. First, ActivePoints aims to generate a hierarchical point-based model as the final representation. Second, ActivePoints employs an interactive segmentation and object organization tool to build the hierarchy. Finally, ActivePoints utilizes modern graphics hardware to achieve efficient and high quality point-based rendering. ActivePoints has been proved to be an efficient system for continuing exploration.
[pdf] 3.6MB
Hybrid Forward Resampling and Volume Rendering, Xiaoru Yuan, Minh X. Nguyen, Hui Xu and Baoquan Chen, , Proceedings of the 2003 Eurographics/IEEE TVCG Workshop on Volume graphics (VG'03), pages 119-127. Tokyo, Japan, June 7-8, 2003
Abstract
The transforming and rendering of discrete objects, such as traditional images (with or without depths) and volumes, can be considered as resampling problem – objects are reconstructed, transformed, filtered, and finally sampled on the screen grids. In resampling practices, discrete samples (pixels, voxels) can be considered either as infinitesimal sample points (simply called points) or samples of a certain size (splats). Resampling can also be done either forwards or backwards in either the source domain or the target domain. In this paper, we present a framework that features hybrid forward resampling for discrete rendering. Specifically, we apply this framework to enhance volumetric splatting. In this approach, minified voxels are taken simply as points filtered in screen space; while magnified voxels are taken as spherical splats. In addition, we develop two techniques for performing accurate and efficient perspective splatting. The first one is to efficiently compute the 2D elliptical geometry of perspectively projected splats; the second one is to achieve accurate perspective reconstruction filter. The results of our experiments demonstrate both the effectiveness of antialiasing and the efficiency of rendering using this approach.