17696206
P-quadtrees: a point and polygon hybrid multi-resolution rendering approach
Point and polygon representations have their respective merits in rendering objects. In this paper, we propose a novel hybrid multi-resolution approach, PQuadtrees, to efficiently render highly detailed objects. PQuadtrees are constructed from geometry images. Both point and polygon are tightly integrated into a uniform structure. While traversing the P-Quadtrees in rendering, the part of surface that face the viewer can be rendered by coarser quad mesh to reduce the numbers of rendering primitives. The shading details can be enhanced by hardware accelerated normal mapping. The view dependent LOD selects the finer hierarchy on silhouette, which is rendered by points. The rendering of large-scale model is greatly accelerated while the visual effect both at the surfaces and the silhouette is guaranteed.
34486970
Simulation of miscible binary mixtures based on lattice Boltzmann method
Miscible fluid mixtures, like pouring honey into water, Coca Cola into strong wine, are common phenomena in our daily life. While two miscible fluids are mixed together, their appearances in terms of colors and shapes will change due to their mixing interaction. The interaction between the mixture components could be regarded as a combination of the diffusing process and demixing process. If the former dominates the interaction, it is miscible; otherwise, it is immiscible. The complex microscopic interplay between the mixture components makes the simulation highly challenging. So far, there have been some dedicated research in computer graphics dealing with immiscible mixtures, but few works have been done focusing on miscible mixtures. In this paper, for the first time, we introduce a two-fluid lattice Boltzmann method (LBM), called TFLBM, applied to miscible binary mixtures. Different from other similar methods, the viscous and diffusing properties of the fluid in our work are considered separately, so that the physical insight is exposed more clearly and rationally. In addition, the operation of LBM is mostly a linear local computation, and graphics processing unit (GPU) has been utilized to achieve real-time simulation. Copyright © 2006 John Wiley & Sons, Ltd.
17132126
Recovery of material under complex illumination conditions
To calculate the inter-reflection between real objects and virtual ones in augmented reality, recovery of material for the real objects is necessary. In this paper, an approach is proposed to recover the material properties from a single high dynamic range image for a homogeneous object under complex illumination conditions. By the method, we first acquire a high dynamic range image for the object, and one or a few environment maps in high dynamic range as illumination of the object. Then a simulated annealing algorithm is employed to solve the inverse rendering problem. Finally, we obtain optimal parameter values for the reflection model in approximating the material of the object. In the course of optimization, image-based lighting and ray tracing techniques are used, and as a result the inter-reflection can be calculated in convenience. In addition, the transparent and translucent properties can be also recovered.
16235665
Real-time 3D fluid simulation on GPU with complex obstacles
In this paper, we solve the 3D fluid dynamics problem in a complex environment by taking advantage of the parallelism and programmability of GPU. In difference from other methods, innovation is made in two aspects. Firstly, more general boundary conditions could be processed on GPU in our method. By the method, we generate the boundary from a 3D scene with solid clipping, making the computation run on GPU despite of the complexity of the whole geometry scene. Then by grouping the voxels into different types according to their positions relative to the obstacles and locating the voxel that determines the value of the current voxel, we modify the values on the boundaries according to the boundary conditions. Secondly, more compact structure in data packing with flat 3D textures is designed at the fragment processing level to enhance parallelism and reduce execution passes. The scalar variables including density and temperature are packed into four channels of texels to accelerate the computation of 3D Navier-Stokes equations (NSEs). The test results prove the efficiency of our method, and as a result, it is feasible to run middle-scale problems of 3D fluid dynamics in an interactive speed for more general environment with complex geometry on PC platform.
39271056
A hybrid representation of environment models in image-based real time walkthrough
In this paper, a hybrid representation of environment models using a combination of points and polygons is proposed. Through the model, a real time walkthrough of a complex environment can be achieved. We start from multiple depth reference images and classify the pixels of images into two categories, corresponding respectively to planar and non-planar surfaces in 3D space, then all the redundant points are removed by a comparison algorithm of sampling rate. For pixels corresponding to nonplanar surfaces, the point representation is maintained, and a local reconstruction and resampling process is employed to re-sample a set of points that distribute more uniformly on the surfaces. The re-sampled points are organized by an OBB-tree according to their space coordinates and a multiresolution structure is built to improve the rendering efficiency. For pixels corresponding to planar surfaces, the plane coefficients are reconstructed and all their appearances in the reference images are merged to texture maps. Under this hybrid representation, texture mapping and point-based rendering are employed to render the novel views, to take full advantage of the acceleration utility of graphics hardware. The algorithm demonstrates the combined advantages of approaches in traditional computer graphics and PBR/IBR, texture mapping for plane surfaces and point-based rendering for high detail surfaces and shapes.
10565448
Singularity analysis of the HALF parallel manipulator with revolute actuators
This paper concerns the singularity of the half parallel manipulator, a novel three degrees of freedom (DOFs) mechanism, with revolute actuators. The parallel manipulator, proposed previously, consists of a base plate, a movable platform, and three connecting legs. It has the advantages in terms of only single-DOF joints and high rotational capability. The parallel manipulator has wide application in the fields of industrial robots, simulators, parallel machine tools and any other manipulating devices that high rotational capability is required. The inverse kinematics problem and Jacobian matrices are recalled firstly. And then all possible singularities of the manipulator are analyzed in detail. The results of the paper are very useful for the apprehension and the application of the manipulator.
4392406
Synthesis and rendering of bidirectional texture functions on arbitrary surfaces
The bidirectional texture function (BTF) is a 6D function that describes the appearance of a real-world surface as a function of lighting and viewing directions. The BTF can model the fine-scale shadows, occlusions, and specularities caused by surface mesostructures. We present algorithms for efficient synthesis of BTFs on arbitrary surfaces and for hardware-accelerated rendering. For both synthesis and rendering, a main challenge is handling the large amount of data in a BTF sample. To addresses this challenge, we approximate the BTF sample by a small number of 4D point appearance functions (PAFs) multiplied by 2D geometry maps. The geometry maps and PAFs lead to efficient synthesis and fast rendering of BTFs on arbitrary surfaces. For synthesis, a surface BTF can be generated by applying a texton-based synthesis algorithm to a small set of 2D geometry maps while leaving the companion 4D PAFs untouched. As for rendering, a surface BTF synthesized using geometry maps is well-suited for leveraging the programmable vertex and pixel shaders on the graphics hardware. We present a real-time BTF rendering algorithm that runs at the speed of about 30 frames/second on a mid-level PC with an ATI Radeon 8500 graphics card. We demonstrate the effectiveness of our synthesis and rendering algorithms using both real and synthetic BTF samples.
6032766
A Novel Volume Constrained Smoothing Method for Meshes
In general, mesh smoothing is performed by minimizing the discrete energy function for the surface. One of the major problems in mesh smoothing is to prevent the mesh from shrinking. In this paper, we propose a novel volume constraint to address the shrinking problem in mesh smoothing. Our key observation is that the mesh can be efficiently smoothed patch by patch in a signal processing manner, and then a local volume preserving constraint can be easily imposed to the energy minimization problem associated with the small patch, called the smoothing stencil, so as to effectively avoid the mesh shrinkage. In our implementation, the smoothing stencil is the 1-ring neighboring region of an edge or a triangle. And the constrained minimization problem is solved by a 2-step approximation method for efficiency. A series of examples demonstrate that the proposed smoothing method can be applied to remove noise from a mesh or remove rough detail from an original mesh to generate a smooth model in object reconstruction and geometry modeling.
16397904
A suite of web-based programs to search for transcriptional regulatory motifs
The identification of regulatory motifs is important for the study of gene expression. Here we present a suite of programs that we have developed to search for regulatory sequence motifs: (i) BioProspector, a Gibbs-sampling-based program for predicting regulatory motifs from co-regulated genes in prokaryotes or lower eukaryotes; (ii) CompareProspector, an extension to BioProspector which incorporates comparative genomics features to be used for higher eukaryotes; (iii) MDscan, a program for finding protein-DNA interaction sites from ChIP-on-chip targets. All three programs examine a group of sequences that may share common regulatory motifs and output a list of putative motifs as position-specific probability matrices, the individual sites used to construct the motifs and the location of each site on the input sequences. The web servers and executables can be accessed at http://seqmotifs.stanford.edu.
2422545
Probe-level measurement error improves accuracy in detecting differential gene expression
MOTIVATION
Finding differentially expressed genes is a fundamental objective of a microarray experiment. Numerous methods have been proposed to perform this task. Existing methods are based on point estimates of gene expression level obtained from each microarray experiment. This approach discards potentially useful information about measurement error that can be obtained from an appropriate probe-level analysis. Probabilistic probe-level models can be used to measure gene expression and also provide a level of uncertainty in this measurement. This probe-level measurement error provides useful information which can help in the identification of differentially expressed genes.


RESULTS
We propose a Bayesian method to include probe-level measurement error into the detection of differentially expressed genes from replicated experiments. A variational approximation is used for efficient parameter estimation. We compare this approximation with MAP and MCMC parameter estimation in terms of computational efficiency and accuracy. The method is used to calculate the probability of positive log-ratio (PPLR) of expression levels between conditions. Using the measurements from a recently developed Affymetrix probe-level model, multi-mgMOS, we test PPLR on a spike-in dataset and a mouse time-course dataset. Results show that the inclusion of probe-level measurement error improves accuracy in detecting differential gene expression.


AVAILABILITY
The MAP approximation and variational inference described in this paper have been implemented in an R package pplr. The MCMC method is implemented in Matlab. Both software are available from http://umber.sbs.man.ac.uk/resources/puma.