Prior works on multi-projector displays have focused primarily on static rigid objects, some focusing on dynamic rigid objects. However, works on projection based displays on deformable dynamic objects have focused only on small scale single projector displays. Tracking a deformable dynamic surface and updating projections precisely in real time on it is a significantly challenging task, even for a single projector system. In this paper, we present the first end-to-end solution for achieving a real-time, seamless display on deformable surfaces using mutliple unsychronized projectors without requiring any prior knowledge of the surface or device parameters. The system first accurately calibrates multiple RGB-D cameras and projectors using the deformable display surface itself, and then using those calibrated devices, tracks the continuous changes in the surface shape. Based on the deformation and projector calibration, the system warps and blends the image content in real-time to create a seamless display on a surface that continuously changes shape. Using multiple projectors and RGB-D cameras, we provide the much desired aspect of scale to the displays on deformable surfaces. Most prior dynamic multi-projector systems assume rigid objects and depend critically on the constancy of surface normals and non-existence of local shape deformations. These assumptions break in deformable surfaces making prior techniques inapplicable. Point-based correspondences become inadequate for calibration, exacerbated with no synchronization between the projectors. A few works address non-rigid objects with several restrictions like targeting semi-deformable surfaces (e.g. human face), or using single coaxial (optically aligned) projector-camera pairs, or temporally synchronized cameras. We break loose from such restrictions and handle multiple projector systems for dynamic deformable fabric-like objects using temporally unsynchronized devices. We devise novel methods using ray and plane-based constraints imposed by the pinhole camera model to address these issues and design new blending methods dependent on 3D distances suitable for deformable surfaces. Finally, unlike all prior work with rigid dynamic surfaces that use a single RGB-D camera, we devise a method that involve all RGB-D cameras for tracking since the surface is not seen completely by a single camera. These methods enable a seamless display at scale in the presence of continuous movements and deformations. This work has tremendous applications on mobile and expeditionary systems where environmentals (e.g. wind, vibrations, suction) cannot be avoided. One can create large displays on tent walls in remote, austere military or emergency operations in minutes to support large scale command and control, mission rehearsal or training operations. It can be used to create displays on mobile and inflatable objects for tradeshows/events and touring edutainment applications.

In a spatially augmented reality system, multiple projectors are tiled on a complex shaped surface to create a seamless display on it. This has several applications in visualization, gaming, education and entertainment. The main challenges in creating seamless and undistorted imagery on such complex shaped surfaces are geometric registration and color correction. Prior methods that provide solutions for the spatial color variation in multi-projector displays assume rectangular overlap regions across the projectors that is possible only on flat surfaces with extremely constrained projector placement. In this article, we present a novel and fully automated method for removing color variations in a multi-projector display on arbitrary shaped smooth surfaces using a general color gamut morphing algorithm that can handle any arbitrarily shaped overlap between the projectors and assures imperceptible color variations across the display surface.

Abstract Segmentation of anatomical structures on 2D images of cardiac exams is necessary for performing 3D volumetric analysis, enabling the computation of parameters for diagnosing cardiovascular disease. In this work, we present robust algorithms to automatically segment cardiac imaging data and generate a volumetric anatomical reconstruction of a patient-specific heart model by propagating active contour output within a patient stack through a self-supervised learning model. Contour initializations are automatically generated, then output segmentations on sparse image slices are transferred and merged across a stack of images within the same heart data set during the segmentation process. We demonstrate whole-heart segmentation and compare the results with ground truth manual annotations. Additionally, we provide a framework to represent segmented heart data in the form of implicit surfaces, allowing interpolation operations to generate intermediary models of heart sections and volumes throughout the cardiac cycle and to estimate ejection fraction.

Dynamic projection mapping (DPM) is becoming increasingly popular, enabling viewers to visualize information on moving and deformable surfaces. Examples include large data visualization on the moving walls of tents deployed in austere remote locations during emergency management or defense operations. A DPM system typically comprises a RGB-D camera and a projector. In this paper, we present the first fully functional DPM system that auto-calibrates (without any physical props like planar checkerboard or rigid 3D objects) and creates a comprehensible display in the presence of large and fast movements by managing jitter and occlusion by passing objects.Prior DPM systems need specific calibration props, manual inputs and in order to deliver sub-pixel calibration accuracy. Recalibration in the face of movement or change in system setup becomes a time consuming process where the calibration prop needs to be brought back. When rendering content using DPM, errors in calibration are exacerbated and the noise in the depth camera leads to jitter, making the projection unreadable or incomprehensible. Occlusion may disrupt operations completely by jumbling up even the unoccluded parts of the display.In this paper we propose key hardware-agnostic methods for DPM calibration and rendering to make DPM systems easily deployable, stable and legible. First, we present a novel projector-camera calibration that does not need synchronization of the devices and leverages the moving surface itself, a counter-intuitive proposition. We project ArUCo markers on the moving surface and use corresponding detected features of these markers in the RGB and depth camera over multiple frames to accurately estimate the intrinsics and extrinsics of both the projector and the RGB-D camera. Second, we present a DPM rendering method that uses Kalman filtering models to reduce jitter and predict the surface shape in the presence of short term occlusions by other static objects. This results in the first DPM system, to the best of our knowledge, that can auto-calibrate in minutes and can render high resolution content like high-resolution text or images comprehensible even in the presence of fast movements, deformations and occlusions. We compare and evaluate the accuracy with prior methods and analyze the effect of surface movement on the calibration accuracy.

In recent years, medical research has made extensive use of Augmented Reality (AR) for visualization. These visualizations provide improved 3D understanding and depth perception for surgeons and medical staff during surgical planning, medical training, and procedures. Often, AR in medicine involves impractical and extensive instrumentation in order to provide the precision needed for clinical use. We propose a mobile AR 3D model registration system for use in a practical, non-instrumented hospital setting. Our registration system takes as input a patient-specific model and overlays it on the patient using an accurate pose registration technique that requires a single marker as a point of reference to initialize a point cloud-based pose refinement technique. Our method is automatic, easy to use, and runs in real-time on a mobile phone. We conduct quantitative and qualitative analysis of the registration. The results confirm that our AR pose registration system produces an accurate and visually correct overlay of the medical data in real-time.

In this article we present a completely automated and scalable multi-projector registration system that allows multiple uncalibrated projectors and cameras on arbitrary shape surfaces. Our method estimates the parameters of multiple uncalibrated tiled or superimposed projectors, the extrinsic parameters of the observing cameras (with known intrinsic parameters), the shape of the illuminated 3D geometry and geometrically registers the projectors on it. This is achieved without using any fiducials, even if part of the surface is visible to only one camera. The method uses a completely automatic approach for cross-correlation and cross-validation of the device parameters and the surface geometry resulting in an accurate registration on the arbitrary unknown geometry that does not need an accurate prior calibration of each of the uncalibrated devices using physical patterns or fiducials. Estimating projector parameters allows for quick recalibration of the system in the face of projector movements, by re-estimating only the parameters of the moved projector and not the entire system. Thus, our work can enable easy deployment of spatially augmented reality environments of different sizes (from small table top objects to large immersive environments), different shapes (inside-looking-out or outside-looking in), and different configurations (tiled or superimposed) using the same proposed method.

We present a new meshing algorithm called guided and augmented meshing, GAMesh, which uses a mesh prior to generate a surface for the output points of a point network. By projecting the output points onto this prior and simplifying the resulting mesh, GAMesh ensures a surface with the same topology as the mesh prior but whose geometric fidelity is controlled by the point network. This makes GAMesh independent of both the density and distribution of the output points, a common artifact in traditional surface reconstruction algorithms. We show that such a separation of geometry fi-om topology can have several advantages especially in single-view shape prediction, fair evaluation of point networks and reconstructing surfaces for networks which output sparse point clouds. We further show that by training point networks with GAMesh, we can directly optimize the vertex positions to generate adaptive meshes with arbitrary topologies. Code and data are available on the project webpage1.

We present a method for dynamic projection mapping on deformable, stretchable and elastic materials (e.g. cloth) using a time of flight (ToF) depth camera (e.g. Azure Kinect or Pico-Flexx) that come equipped with an IR camera. We use Bezier surfaces to model the projection surface without explicitly modeling the deformation. We devise an efficient tracking method that tracks the boundary of the surface material using the IR-Depth camera. This achieves realistic mapping even in the interior of the surface, with simple markers (e.g. black dots or squares) or without markers entirely, such that the projection appears to be printed on the material. The surface representation is updated in real-time using GPU based computations. Further, we also show that the speed of these updates is limited by the camera frame rate and therefore can be adopted for higher speed cameras as well. This technique can be used to project on several stretchable moving materials to change their appearance.

Abstract This work presents a shape decomposition algorithm to partition a complex high genus surface into simple primitives, each of which is a torus. First, using a novel iterative algorithm, handle and tunnel fundamental cycles on the surface are progressively localized. Then, the problem of computing the splitting cycles that produce such a tori decomposition is posed as a min‐cut problem on the mesh's dual graph with earlier computed tunnels as source and target. The edge weights for the min‐cut problem are designed for the cut to be geometry‐aware. We present an implementation and demonstrate the results of our algorithm on numerous examples.

The collagen fiber organization plays an important role in controlling the mechanical strength of the extracellular matrix tissues and in the cornea is thought to control tissue shape and refractive power. In the case of the cornea, collagen fibers run in orthogonal directions, interweaving, branching and anastomosing, that can be imaged using second harmonic-generated signals. But the complexity of the structure makes it difficult for identifying tunnels using previous methods. In the proposed work, we apply an efficient graph based algorithm to find fundamental cycles, including both tunnels and non-tunnels. After tightening the cycle and decoupling composite cycles, we classify the resulting fundamental cycles based on their geometric properties and their relationship between each other. The utility of our tunnel computation and location algorithm is demonstrated on various example cornea structures from various animals.

Abstract Radiometric compensation methods remove the effect of the underlying spatially varying surface reflectance of the texture when projecting on textured surfaces. All prior work sample the surface reflectance dependent radiometric transfer function from the projector to the camera at every pixel that requires the camera to observe tens or hundreds of images projected by the projector. In this paper, we cast the radiometric compensation problem as a sampling and reconstruction of multi‐dimensional radiometric transfer function that models the color transfer function from the projector to an observing camera and the surface reflectance in a unified manner. Such a multi‐dimensional representation makes no assumption about linearity of the projector to camera color transfer function and can therefore handle projectors with non‐linear color transfer functions(e.g. DLP, LCOS, LED‐based or laser‐based). We show that with a well‐curated sampling of this multi‐dimensional function, achieved by exploiting the following key properties, is adequate for its accurate representation: (a) the spectral reflectance of most real‐world materials are smooth and can be well‐represented using a lower‐dimension function; (b) the reflectance properties of the underlying texture have strong redundancies – for example, multiple pixels or even regions can have similar surface reflectance; (c) the color transfer function from the projector to camera have strong input coherence. The proposed sampling allows us to reduce the number of projected images that needs to be observed by a camera by up to two orders of magnitude, the minimum being only two. We then present a new multi‐dimensional scattered data interpolation technique to reconstruct the radiometric transfer function at a high spatial density (i.e. at every pixel) to compute the compensation image. We show that the accuracy of our interpolation technique is higher than any existing methods.

In this work, we propose an original scheme for generic content-based retrieval of marker-based motion capture data. It works on motion capture data of arbitrary subject types and arbitrary marker attachment and labelling conventions. Specifically, we propose a novel motion signature to statistically describe both the high-level and the low-level morphological and kinematic characteristics of a motion capture sequence, and conduct the content-based retrieval by computing and ordering the motion signature distance between the query and every item in the database. The distance between two motion signatures is computed by a weighted sum of differences in separate features contained in them. For maximum retrieval performance, we propose a method to pre-learn an optimal set of weights for each type of motion in the database through biased discriminant analysis, and adaptively choose a good set of weights for any given query at the run time. Excellence of the proposed scheme is experimentally demonstrated on various data sets and performance metrics.

Distortions due to perspective projection is often described under the umbrella term of foreshortening in computer graphics and are treated the same way. However, a large body of literature from artists, perceptual psychologists and perception scientists have shown that the perception of these distortions is different in different situations. While the distortions themselves depend on both the depth and the orientation of the object with respect to the camera image plane, the perception of these distortions depends on other depth cues present in the image. In the absence of any depth cue or prior knowledge about the objects in the scene, the visual system finds it hard to correct the foreshortening automatically and such images need user input and external algorithmic distortion correction.In this paper, we claim that the shape distortion is more perceptible than area distortion, and quantify such perceived foreshortening as the non-uniformity across the image, of the ratio e of the differential areas of an object in the scene and its projection. We also categorize foreshortening into uniform and non-uniform foreshortening. Uniform foreshortening is perceived by our visual system as a distortion, even if e is uniform across the image, only when comparative objects of known sizes are present in the image. Non-uniform foreshortening is perceived when there is no other depth cue in the scene that can help the brain to correct for the distortion. We present a unified solution to correct these distortions in one or more non-occluded foreground objects by applying object-specific segmentation and affine transformation of the segmented camera image plane. Our method also ensures that the background undergoes minimal distortion and preserves background features during this process. This is achieved efficiently by solving Laplace's equations with Dirichlet boundary conditions, assisted by a simple and intuitive user interface.

Abstract Many works focus on multi‐spectral capture and analysis, but multi‐spectral display still remains a challenge. Most prior works on multi‐primary displays use ad‐hoc narrow band primaries that assure a larger color gamut, but cannot assure a good spectral reproduction. Content‐dependent spectral analysis is the only way to produce good spectral reproduction, but cannot be applied to general data sets. Wide primaries are better suited for assuring good spectral reproduction due to greater coverage of the spectral range, but have not been explored much. In this paper we explore the use of wide band primaries for accurate spectral reproduction for the first time and present the first content‐independent multi‐spectral display achieved using superimposed projections with modified wide band primaries. We present a content‐independent primary selection method that selects a small set of n primaries from a large set of m candidate primaries where m > n. Our primary selection method chooses primaries with complete coverage of the range of visible wavelength (for good spectral reproduction accuracy), low interdependency (to limit the primaries to a small number) and higher light throughput (for higher light efficiency). Once the primaries are selected, the input values of the different primary channels to generate a desired spectrum are computed using an optimization method that minimizes spectral mismatch while maximizing visual quality. We implement a real prototype of multi‐spectral display consisting of 9‐primaries using three modified conventional 3‐primary projectors, and compare it with a conventional display to demonstrate its superior performance. Experiments show our display is capable of providing large gamut assuring a good visual appearance while displaying any multi‐spectral images at a high spectral accuracy.

Simultaneous modification and navigation of massive 3D models are difficult because repeated data edits affect the data layout and coherency on a secondary storage, which in turn affect the interactive out-of-core rendering performance. In this paper, we propose a novel approach for distributed data management for simultaneous interactive navigation and modification of massive 3D data using the readily available infrastructure of a tiled display. Tiled multi-displays, projection or LCD panel based, driven by a PC cluster, can be viewed as a cluster of storage-compute-display (SCD) nodes. Given a cluster of SCD node infrastructure, we first propose a distributed memory hierarchy for interactive rendering applications. Second, in order to further reduce the latency in such applications, we propose a new data partitioning approach for distributed storage among the SCD nodes that reduces the variance in the data load across the SCD nodes. Our data distribution method takes in a data set of any size, and reorganizes it into smaller partitions, and stores it across the multiple SCD nodes. These nodes store, manage, and coordinate data with other SCD nodes to simultaneously achieve interactive navigation and modification. Specifically, the data is not duplicated across these distributed secondary storage devices. In addition, coherency in data access, due to screen-space adjacency of adjacent displays in the tile, as well as object space adjacency of the data sets, is well leveraged in the design of the data management technique. Empirical evaluation on two large data sets, with different data density distribution, demonstrates that the proposed data management approach achieves superior performance over alternative state-of-the-art methods.

Earlier work has explored enhancing the perceived resolution of a display by shifting multiple different low-resolution images by fractions of a pixel and overlaying them in a temporally multiplexed fashion. This increases the manufacturing cost and also sacrifices the temporal resolution that can compromise other capabilities like 3D active stereo. In this paper we propose a method to achieve the same goal in projectors by performing the pixel shift and superposition optically by introducing a simple and inexpensive optical ensemble of a set of lenses on the projector light path. This does not sacrifice the temporal resolution and is extremely easy to implement in practice. However, instead of overlaying different images, we overlay an image with one or more sub-pixel shifted copies of itself. Therefore, we seek a single n×n image which when shifted and overlaid with itself creates a perceptually closer to a higher resolution 2n × 2n target image. This changes the optimization formulation significantly and requires solving a system of sparse linear equations. We take advantage of this sparsity and design a parallel implementation of this optimization in GPUs for real-time computation of the input image critical for its practical implementation. But, since this system is more constrained that using multiple overlaid images, the enhancement of resolution is compromised. However, since the optical design is very simple and inexpensive, it can be deployed on a variety of low-cost projectors and still offer a significant image quality benefit.

The use of wide angle lens on commodity cameras are becoming increasingly popular. However, this leads to image distortions due to the large difference in relative orientation of the different foreground objects with respect to the camera's image plane. More importantly, these distortions are different in different parts of the image since it depends entirely on the position and orientation of the foreground object with respect to the image plane. Such distortions often manifest themselves as objects in the foreground appearing fatter than they are supposed to be or parts thereof (e.g. hands or head of people) looking disproportionately larger than the rest of them. Though there are earlier works addressing other common distortions in cameras like radial distortions, little attention has been given to this problem. In this paper, we present an effective method to remove such distortions in foreground objects minimally distorting the background. This is achieved efficiently using a mesh-based pixel displacement technique assisted by a simple and intuitive user interface design.

Digital projection technology has improved significantly in recent years. But, the relationship of cost with respect to available resolution in projectors is still super-linear. In this paper, we present a method that uses projector light modulator panels (e.g. LCD or DMD panels) of resolution n X n to create a perceptually close match to a target higher resolution cn X cn image, where c is a small integer greater than 1. This is achieved by enhancing the resolution using smaller pixels at specific regions of interest like edges. A target high resolution image ( cn X cn ) is first decomposed into (a) a high resolution ( cn X cn ) but sparse edge image , and (b) a complementary lower resolution ( n X n ) non-edge image . These images are then projected in a time sequential manner at a high frame rate to create an edge-enhanced image -- an image where the pixel density is not uniform but changes spatially. In 3D ready projectors with readily available refresh rate of 120Hz, such a temporal multiplexing is imperceptible to the user and the edge-enhanced image is perceptually almost identical to the target high resolution image. To create the higher resolution edge image, we introduce the concept of optical pixel sharing . This reduces the projected pixel size by a factor of 1/ c 2 while increasing the pixel density by c 2 at the edges enabling true higher resolution edges. Due to the sparsity of the edge pixels in an image we are able to choose a sufficiently large subset of these to be displayed at the higher resolution using perceptual parameters. We present a statistical analysis quantifying the expected number of pixels that will be reproduced at the higher resolution and verify it for different types of images.

Analysis of Confocal Laser Scanning Microscopy (CLSM) images is gaining popularity in developmental biology for understanding growth dynamics. The automated analysis of such images is highly desirable for efficiency and accuracy. The first step in this process is segmentation and tracking leading to computation of cell lineages. In this paper, we present efficient, accurate, and robust segmentation and tracking algorithms for cells and detection of cell divisions in a 4D spatio-temporal image stack of a growing plant meristem. We show how to optimally choose the parameters in the watershed algorithm for high quality segmentation results. This yields high quality tracking results using cell correspondence evaluation functions. We show segmentation and tracking results on Confocal laser scanning microscopy data captured for 72 hours at every 3 hour intervals. Compared to recent results in this area, the proposed algorithms provide significantly longer cell lineages and more comprehensive identification of cell divisions.

Solid state drives (SSDs) are emerging as an alternative storage medium to HDDs. SSDs have performance characteristics (e.g., fast random reads) that are very different from those of HDDs. Because of the high performance of SSDs, there are increasingly more research efforts to redesign the established techniques that are optimized for HDDs, to work well with SSDs. In this paper we focus on computing cache-coherent layouts of large-scale models for SSDs. It has been demonstrated that cache-oblivious layouts perform well for various applications running on HDDs. However, computing cache-oblivious layouts for large-models is known to be very expensive. Also these layouts cannot be maintained efficiently for dynamically changing models. Utilizing the properties of SSDs we propose an efficient layout computation method that produces a page-based cache-aware layout for SSDs. We show that the performance of our layout can be maintained under dynamic changes on the model and is similar to the cache-oblivious layout optimized for static models. We demonstrate the benefits of our method for large-scale walkthrough scene editing and rendering, and collision detection.

Large scale and structurally complex volume datasets from high-resolution 3D imaging devices or computational simulations pose a number of technical challenges for interactive visual analysis. In this paper, we present the first integration of a multiscale volume representation based on tensor approximation within a GPU-accelerated out-of-core multiresolution rendering framework. Specific contributions include (a) a hierarchical brick-tensor decomposition approach for pre-processing large volume data, (b) a GPU accelerated tensor reconstruction implementation exploiting CUDA capabilities, and (c) an effective tensor-specific quantization strategy for reducing data transfer bandwidth and out-of-core memory footprint. Our multiscale representation allows for the extraction, analysis and display of structural features at variable spatial scales, while adaptive level-of-detail rendering methods make it possible to interactively explore large datasets within a constrained memory footprint. The quality and performance of our prototype system is evaluated on large structurally complex datasets, including gigabyte-sized micro-tomographic volumes.

Abstract A feature‐oriented generic progressive lossless mesh coder (FOLProM) is proposed to encode triangular meshes with arbitrarily complex geometry and topology. In this work, a sequence of levels of detail (LODs) are generated through iterative vertex set split and bounding volume subdivision. The incremental geometry and connectivity updates associated with each vertex set split and/or bounding volume subdivision are entropy coded. Due to the visual importance of sharp geometric features, the whole geometry coding process is optimized for a better presentation of geometric features, especially at low coding bitrates. Feature‐oriented optimization in FOLProM is performed in hierarchy control and adaptive quantization. Efficient coordinate representation and prediction schemes are employed to reduce the entropy of data significantly. Furthermore, a simple yet efficient connectivity coding scheme is proposed. It is shown that FOLProM offers a significant rate‐distortion (R‐D) gain over the prior art, which is especially obvious at low bitrates.

Given a data layout of a large walkthrough scene, we present a novel and simple spatial hierarchy on the disk-pages of the layout that has notable advantages over a conventional spatial hierarchy on the scene geometry. Assume that each disk-page consists of a set of triangles whose bounding boxes are computed. A spatial hierarchy of the walkthrough space is constructed, not with the given scene, but with the bounding boxes of disk-pages. The leaf nodes of the spatial-hierarchy refer directly to the page numbers of the pages of the bounding box it contains. We call this hierarchy on the pages as the disk-page hierarchy. We also propose a self-contained disk-page format that would suit this data structure well. Further, we present a new cache-oblivious graph-based data layout algorithm called the 2-factor layout that would preserve the proximity and orientation properties of the primitives in the layout. Walkthrough experiments have been conducted on a city scene consisting of over 110M triangles. Our system renders this scene on a laptop within a one pixel projection error at over 20 fps with simple texture substitution based simplification of distant objects, and with no explicit data/cache management.

Shape simplification and re-sampling of underlying point-sampled surfaces under user-defined error bounds is an important and challenging issue. Based on the regular triangulation of the Gaussian sphere and the surface normals mapping onto the Gaussian sphere, a Gaussian sphere based re-sampling scheme is presented that generates a non-uniformly curvature-aware simplification of the given point-sampled model. Owing to the theoretical analysis of shape isophotic error metric for did that Gaussian sphere based sampling, the proposed simplification scheme provides a convenient way to control the re-sampling results under a user-specified error metric bound. The novel algorithm has been implemented and demonstrated on several examples.

Abstract We present a graph algorithm to find fundamental cycles aligned with the principal curvature directions of a surface. Specifically, we use the tree‐cotree decomposition of graphs embedded in manifolds, guided with edge weights, in order to produce these cycles. Our algorithm is very quick compared to existing methods, with a worst case running time ofO(nlogn+gn) wherenis the number of faces andgis the surface genus. Further, its flexibility to accommodate different weighting functions and to handle boundaries may be used to produce cycles suitable for a variety of applications and models.

Multi-projector displays show significant spatial variation in 3D color gamut due to variation in the chromaticity gamuts across the projectors, vignetting effect of each projector and also overlap across adjacent projectors. In this paper we present a new constrained gamut morphing algorithm that removes all these variations and results in true color seamlessness across tiled multiprojector displays. Our color morphing algorithm adjusts the intensities of light from each pixel of each projector precisely to achieve a smooth morphing from one projector's gamut to the other's through the overlap region. This morphing is achieved by imposing precise constraints on the perceptual difference between the gamuts of two adjacent pixels. In addition, our gamut morphing assures a C1 continuity yielding visually pleasing appearance across the entire display.We demonstrate our method successfully on a planar and a curved display using both low and high-end projectors. Our approach is completely scalable, efficient and automatic. We also demonstrate the real-time performance of our image correction algorithm on GPUs for interactive applications. To the best of our knowledge, this is the first work that presents a scalable method with a strong foundation in perception and realizes, for the first time, a truly seamless display where the number of projectors cannot be deciphered.

In this paper, we propose a generic point cloud encoder that provides a unified framework for compressing different attributes of point samples corresponding to 3D objects with arbitrary topology. In the proposed scheme, the coding process is led by an iterative octree cell subdivision of the object space. At each level of subdivision, positions of point samples are approximated by the geometry centers of all tree-front cells while normals and colors are approximated by their statistical average within each of tree-front cells. With this framework, we employ attribute-dependent encoding techniques to exploit different characteristics of various attributes. All of these have led to significant improvement in the rate-distortion (R-D) performance and a computational advantage over the state of the art. Furthermore, given sufficient levels of octree expansion, normal space partitioning and resolution of color quantization, the proposed point cloud encoder can be potentially used for lossless coding of 3D point clouds.

Representing a triangulated two manifold using a single triangle strip is an NP-complete problem. By introducing a few Steiner vertices, recent works find such a single-strip and hence a linear ordering of edge-connected triangles of the entire triangulation. In this paper, we highlight and exploit this linear order in efficient triangle-strip management for high-performance rendering. We present new algorithms to generate weighted single-strip representations that respect different constraint-based clustering of triangles. These functional constraints can be application dependent; for example, normal-based constraints for efficient visibility culling or spatial constraints for highly coherent vertex-caching. We also present a hierarchical single-strip-management strategy for high-performance interactive 3D rendering.

In this paper we explore the algorithmic space in which stripification, simplification and geometric compression of triangulated 2-manifolds overlap. Edge-collapse/uncollapse based geometric simplification algorithms develop a hierarchy of collapses such that during uncollapse the reverse order has to be maintained. We show that restricting the simplification and refinement operations only to, what we call, the collapsible edges creates hierarchyless simplification in which the operations on one edge can be performed independent of those on another. Although only a restricted set of edges is used for simplification operations, we prove topological results to show that, with minor retriangulation, any triangulated 2-manifold can be reduced to either a single vertex or a single edge using the hierarchyless simplification, resulting in extreme simplification. The set of collapsible edges helps us analyze and relate the similarities between simplification, stripification and geometric compression algorithms. We show that the maximal set of collapsible edges implicitly describes a triangle strip representation of the original model. Further, these strips can be effortlessly maintained on multiresolution models obtained through any sequence of hierarchyless simplifications on these collapsible edges. Due to natural relationship between stripification and geometric compression, these multi-resolution models can also be efficiently compressed using traditional compression algorithms. We present algorithms to find the maximal set of collapsible edges and to reorganize these edges to get the minimum number of connected components of these edges. An order-independent simplification and refinement of these edges is achieved by our novel data structure and we show the results of our implementation of view-dependent, dynamic, hierarchyless simplification. We maintain a single triangle strip across all multi-resolution models created by the view-dependent simplification process. We present a new algorithm to compress the models using the triangle strips implicitly defined by the collapsible edges.

Abstract The concept of tiled displays can be successful only if such displays are made to look like a single display perceptually. The two issues that need to be solved to achieve this goal are geometric correction and color seamlessness of images spanning across tiles. Geometric correction algorithms borrow pin‐hole camera models to model projector display geometry. In this paper, we introduce an abstract modeling function that describes the color seen by a viewer when displayed by a display device. Though this function can be used to model color displayed by any common display device, in this paper, we use it to model color in multiprojector display systems. We use the model to explain the reasons for different types of color variations in a multiprojector display, to compare different color correction algorithms, and to derive such algorithms directly from the model.

This video illustrates a new method for subdividing the surface of a triangulated 3d polyhedron, without changing the geometry of the model, so that the triangles of the subdivided mesh can be ordered into a single triangle strip. Our method guarantees that the subdivided mesh has at most 3/2 the original number of triangles, and in practice performs much better. Our strips can be used not only for efficient rendering, but also for other applications including the generation of space filling curves.

In this paper, we introduce a method to represent a given triangular model using a single triangle strip. Since this problem is NP-complete, we break the limitation by splitting adjacent triangles when necessary. The common edge is split at the mid-point, and the newly formed triangles are coplanar with their parent triangles. Hence, the resulting geometry of the model is visually and topologically identical to the original triangular model. Our method can develop any edge-connected oriented 2-manifold of arbitrary topology, with or without boundary, into a single strip. Our stripification method can be controlled to start and end at triangles incident on specific vertices. Further, an acyclic set of edges of the input model can be marked as "constraint edges" and our method can generate a single strip that does not cross over these edges, but still cover the whole model.

Abstract Triangle strips have been widely used for efficient rendering. It is NP‐complete to test whether a given triangulated model can be represented as a single triangle strip, so many heuristics have been proposed to partition models into few long strips. In this paper, we present a new algorithm for creating a single triangle loop or strip from a triangulated model. Our method applies a dual graph matching algorithm to partition the mesh into cycles, and then merges pairs of cycles by splitting adjacent triangles when necessary. New vertices are introduced at midpoints of edges and the new triangles thus formed are coplanar with their parent triangles, hence the visual fidelity of the geometry is not changed. We prove that the increase in the number of triangles due to this splitting is 50% in the worst case, however for all models we tested the increase was less than 2%. We also prove tight bounds on the number of triangles needed for a single‐strip representation of a model with holes on its boundary. Our strips can be used not only for efficient rendering, but also for other applications including the generation of space filling curves on a manifold of any arbitrary topology. Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Geometric algorithms, Triangulation, Stripification. G.2.2 [Graph algorithms]: Hamiltonian Path, Hamiltonian Cycle, Perfect Matching.

We present a fast, memory efficient algorithm that generates a manifold triangular mesh S passing through a set of unorganized points P R 3. Nothing is assumed about the geometry, topology or presence of boundaries in the data set except that P is sampled from a real manifold surface. The speed of our algorithm is derived from a projection‐based approach we use to determine the incident faces on a point. We define our sampling criteria to sample the surface and guarantee a topologically correct mesh after surface reconstruction for such a sampled surface. We also present a new algorithm to find the normal at a vertex, when the surface is sampled according our given criteria. We also present results of our surface reconstruction using our algorithm on unorganized point clouds of various models.

This paper presents a new algorithm for immersive teleconferencing, which addresses the problem of registering and blending multiple images together to create a single seamless panorama. In the immersive teleconference paradigm, one frame of the teleconference is a panorama that is constructed from a compound-image sensing device. These frames are rendered at the remote site on a projection surface that surrounds the user, creating an immersive feeling of presence and participation in the teleconference. Our algorithm efficiently creates panoramic frames for a teleconference session that are both geometrically registered and intensity blended. We demonstrate a prototype that is able to capture images from a compound-image sensor, register them into a seamless panoramic frame, and render those panoramic frames on a projection surface at 30 frames per second.

We present a new approach for simplifying models composed of polygons or spline patches. Given an input model, the algorithm computes a new representation of the model in terms of triangular Bezier patches. It performs a series of geometric operations, consisting of patch merging and swapping diagonals, and makes use of batch connectivity information to generate C-LODs (curved levels-of-detail). Each C-LOD is represented using cubic triangular Bezier patches. The C-LODs provide a compact representation for storing the model. The algorithm tries to minimize the surface deviation error and maintains continuity at patch boundaries. Given the CLODs, the algorithm can generate their polygonal approximations using static and dynamic tessellation schemes. It has been implemented and we highlight its performance on a number of polygonal and spline models.

In this paper, we present an efficient algorithm for contact determination between spline models. We make use of a new hierarchy, called ShellTree, that comprises of spherical shells and oriented bounding boxes. Each spherical shell corresponds to a portion of the volume between two concentric spheres. Given large spline models, our algorithm decomposes each surface into Bézier patches as part of pre‐processing. At runtime it dynamically computes a tight fitting axis‐aligned bounding box across each Bézier patch and efficiently checks all such boxes for overlap. Using off‐line and on‐line techniques for tree construction, our algorithm computes ShellTrees for Bézier patches and performs fast overlap tests between them to detect collisions. The overall approach can trade off runtime performance for reduced memory requirements. We have implemented the algorithm and tested it on large models, each composed of hundred of patches. Its performance varies with the configurations of the objects. For many complex models composed of hundreds of patches, it can accurately compute the contacts in a few milliseconds.

We present algorithms and systems for interactive boundary computation of Boolean combinations of sculptured solids. The algorithm is applicable to all spline solids and computes an accurate boundary representation. To speed up the computation, the algorithm exploits parallelism at all stages. It has been implemented on a multi‐processor SGI and takes one second on average per boolean operation to compute the boundary of high degree primitives. The system has also been integrated with an immersive design and manipulation environment. The resulting system is able to interactively evaluate boundaries of the models, display them for model validation and place them at appropriate position using collision detection algorithms.

B-Splines, in general, and Non-Uniform Rational B-Splines (NURBS), in particular, have become indispensable modeling primitives in computer graphics and geometric modeling applications. In this paper, a novel high-performance architecture for the computation of uniform, nonuniform, rational, and nonrational B-Spline curves and surfaces is presented. This architecture has been derived through a sequence of steps. First, a systolic architecture for the computation of the basis function values, the basis function evaluation array (the BFEA), is developed. Using the BFEA as its core, an architecture for the computation of NURBS curves is constructed. This architecture is then extended to compute NURBS surfaces. Finally, this architecture is augmented to compute the surface normals, so that the output from this architecture can be directly used for rendering the NURBS surface.