As the global population ages, effective rehabilitation and mobility aids will become increasingly critical. Gait assistive robots are promising solutions, but designing adaptable controllers for various impairments poses a significant challenge. This paper presented a Human-In-The-Loop (HITL) simulation framework tailored specifically for gait assistive robots, addressing unique challenges posed by passive support systems. We incorporated a realistic physical human-robot interaction (pHRI) model to enable a quantitative evaluation of robot control strategies, highlighting the performance of a speed-adaptive controller compared to a conventional PID controller in maintaining compliance and reducing gait distortion. We assessed the accuracy of the simulated interactions against that of the real-world data and revealed discrepancies in the adaptation strategies taken by the human and their effect on the human's gait. This work underscored the potential of HITL simulation as a versatile tool for developing and fine-tuning personalized control policies for various users.

3D window details for buildings are important in many 3D simulation and visualization applications. However, they are not easy to acquire or reconstruct. Thus, many 3D city models have no 3D windows, but only 2D planar textures for their façades (i.e., textured LoD2 CityGML models). Many procedural methods have been proposed to generate 3D façade details from images. However, they usually require tedious efforts to create a procedural grammar to achieve desired results, and lack consideration of window semantics which is a useful building property. In this paper, we propose a novel semantics-aware method for adding 3D window details to textured LoD2 CityGML models. We propose a two-level deep learning-based windowpane detection followed by processing and adjusting the detection results then generating and adding 3D windows to the building models. Different from existing methods, we focus on adding window details considering the semantics (i.e., frames and panes). Moreover, our method does not require tedious reconstruction or grammar creation efforts. It extracts the information present in the texture itself only, finds and adjusts the patterns and shapes from the detection results in an unsupervised and efficient manner to achieve neat window parsing results. Specifically, we propose clustering-based window/pane alignment, neatness-based window image voting, grid-based symmetry and thickness filtering, and fitting-based window-top modeling. Experiments on representative 3D city datasets and illustrative applications demonstrate the effectiveness and usefulness of our method.

Abstract We propose a high-performance texture streaming system for real-time rendering of large 3D cities with millions of textures. Our main contribution is a texture streaming system that automatically adjusts the streaming workload at runtime based on measured frame latencies, specifically addressing the high memory binding costs of hardware virtual texturing which causes frame rate stuttering. Our system streams textures in parallel with prioritization based on GPU computed mesh perceptibility, and these textures are cached in a sparse partially resident image at runtime without the need for a texture preprocessing step. In addition, we improve rendering quality by minimizing texture pop-in artifacts using a color blending scheme based on mipmap levels. We evaluate our texture streaming system using three structurally distinct datasets with many textures and compared it to a baseline, a game engine, and our prior method. Results show an 8X improvement in rendering performance and 7X improvement in rendering quality compared to the baseline.

Nowadays, increasing attention has been drawn to hybrid 2D-3D visualization tools, while evaluating them with a convenient and objective tool has only been carried out in a small number of areas. In this study, a revised radar chart-based usability evaluation approach was proposed. The approach was adopted to evaluate the hybrid 2D-3D radar display in air traffic management. The holding stack in air traffic management is analyzed and simulated, two generic tasks are designed accordingly. The hybrid 2D-3D radar display settings are evaluated based on six indicators from eye-tracking and brain dynamics data, namely, the frequency of fixation, fixation mean duration, fixation time on an area of interest, emotion, workload, and stress. The results reveal that the hybrid 2D-3D radar display induces spatial memory loss and high workload, while requires a shorter fixation duration.

We introduce a novel, high performing, bandwidth-aware texture streaming system for progressive texturing of buildings in large 3D cities, with optional texture pre-processing. We seek to maintain high and consistent texture streaming performance across different city datasets, and to address the high memory binding latency in hardware virtual textures. We adopt the sparse partially-resident image to cache mesh textures at runtime and propose to allocate memory persistently, based on mesh visibility weightings and estimated GPU bandwidth. We also retain high quality rendering by minimizing texture pop-ins when transitioning between texture mipmaps. We evaluate our texture streaming system on large city datasets, including a tile-based dataset with 56K large atlases and a dataset containing 5.7M individual textures. Results indicate fast and robust streaming and rendering performance with minimal pop-in artifacts suitable for real-time rendering of large 3D cities.

In many 3D applications, building models in polygon-soup representation are commonly used for the purposes of visualization, for example, in movies and games. Their appearances are fine, however geometry-wise, they may have limited information of connectivity and may have internal intersections between their parts. Therefore, they are not well-suited to be directly used in 3D geospatial applications, which usually require geometric analysis. For an input building model in polygon-soup representation, we propose a novel appearance-driven approach to interactively convert it to a two-manifold model, which is more well-suited for 3D geospatial applications. In addition, the level of detail (LOD) can be controlled interactively during the conversion. Because a model in polygon-soup representation is not well-suited for geometric analysis, the main idea of the proposed method is extracting the visual appearance of the input building model and utilizing it to facilitate the conversion and LODs generation. The silhouettes are extracted and used to identify the features of the building. After this, according to the locations of these features, horizontal cross-sections are generated. We then connect two adjacent horizontal cross-sections to reconstruct the building. We control the LOD by processing the features on the silhouettes and horizontal cross-sections using a 2D approach. We also propose facilitating the conversion and LOD control by integrating a variety of rasterization methods. The results of our experiments demonstrate the effectiveness of our method.

Polygon soup building models are fine for visualization purposes such as in games and movies. They, however, are not suitable for 3D geospatial applications which require geometrical analysis, since they lack connectivity information and may contain intersections internally between their parts. In this paper, we propose an appearance-driven method to interactively convert an input polygon soup building model to a two-manifold mesh, which is more suitable for 3D geospatial applications. Since a polygon soup model is not suitable for geometrical analysis, our key idea is to extract and utilize the visual appearance of the input building model for the conversion. We extract the silhouettes and use them to identify the features of the building. We then generate horizontal cross sections based on the locations of the features and then reconstruct the building by connecting two neighbouring cross sections. We propose to integrate various rasterization techniques to facilitate the conversion. Experimental results show the effectiveness of the proposed method.

Interactive rendering of translucent materials in virtual worlds has always proved to be challenging. In our work, we develop a voxel illumination framework for translucent materials illuminated by area lights. Our voxel illumination framework consists of two voxel structures. They are the Enhanced Subsurface Light Propagation Volumes (ESLPV), which handles the local translucent material appearance and the Light Propagation Volumes (LPV), which handles indirect illumination for the entire scene. Using a set of sparsely distributed Poisson disk samples in the ESLPV and LPV, illumination can be gathered from area lights. A uniform set of Poisson disk samples on the translucent objects is resampled and chosen as Translucent Planar Lights (TPLs) and is used to distribute lighting from translucent objects into the LPV by an additional gathering process. Our technique allows for direct and indirect illuminations from highly scattering translucent materials to be rendered interactively under area lighting at good quality. We can achieve similar effects, such as scattered light illumination from translucent materials, when compared to offline renderers without precomputations.

Abstract In this paper, we propose an approach to interactively author the bending and twisting motions of short plants using hand gestures, especially suitable for grass, flowers, and leaves. Our method is based on the observations that hand motions can represent the bending and twisting motions of short plants and using a hand to describe motions is natural and proficient for human. We therefore use a hand as a “puppet” to author the animation of one single short plant based on transferring the motions of a hand to the motions of a short plant. We first author the global motions of the short plant followed by the motions of its elements such as leaves and flowers. We also propose a framework to utilize the animation results to animate a field of short plants and further adjust the motion effects according to the properties of the short plants, such as rigidity. As a result, users can intuitively and rapidly author and generate their desired motions of short plants under the influence of external forces. Especially, our method is accessible to non‐expert users and suitable for fast prototyping and authoring specific motions of short plants such as in cartoons.

Interactive rendering of illumination from area lights in virtual worlds has always proved to be challenging. In this paper, we extend the work of multi resolution rendering for direct illumination from area lights. We propose a deferred shading method for direct illumination which subdivides screenspace into multi resolution 2D-fragments in which higher resolution fragments are created to represent geometric and depth discontinuities as well as shadow boundaries. To detect shadow boundaries, our subdivision scheme, sub-fragment visibility test (SFVT), performs a visibility discontinuity check within each fragment and subdivides the fragment to a higher resolution level if discontinuity is found. In addition, our proposed gradient aware screenspace subdivision (GASS) algorithm accelerates the refinement by increasing the number of subdivisions based on gradient differences. Our technique utilizes the streamcompaction feature of the transform feedback shader (TFS) in the graphics shading pipeline to filter out fragments for soft shadow refinement. A single pass screenspace irradiance upsampling scheme which uses radial basis functions (RBF) is proposed for interpolating scattered fragments. This reduces artifacts caused by large fragments. OuInteractive rendering of illumination from area lights in virtual worlds has always proved to be challenging. In this paper, we extend the work of multi resolution rendering for direct illumination from area lights. We propose a deferred shading method for direct illumination which subdivides screenspace into multi resolution 2D-fragments in which higher resolution fragments are created to represent geometric and depth discontinuities as well as shadow boundaries. To detect shadow boundaries, our subdivision scheme, sub-fragment visibility test (SFVT), performs a visibility discontinuity check within each fragment and subdivides the fragment to a higher resolution level if discontinuity is found. In addition, our proposed gradient aware screenspace subdivision (GASS) algorithm accelerates the refinement by increasing the number of subdivisions based on gradient differences. Our technique utilizes the stream-compaction feature of the transform feedback shader (TFS) in the graphics shading pipeline to filter out fragments for soft shadow refinement. A single pass screenspace irradiance upsampling scheme which uses radial basis functions (RBF) is proposed for interpolating scattered fragments. This reduces artifacts caused by large fragments. Our technique does not require precomputations and is able to run at interactive rates.r technique does not require precomputations and is able to run at interactive rates.

3D models of humans are commonly used within computer graphics and vision, and so the ability to distinguish between body shapes is an important shape retrieval problem. We extend our recent paper which provided a benchmark for testing non-rigid 3D shape retrieval algorithms on 3D human models. This benchmark provided a far stricter challenge than previous shape benchmarks. We have added 145 new models for use as a separate training set, in order to standardise the training data used and provide a fairer comparison. We have also included experiments with the FAUST dataset of human scans. All participants of the previous benchmark study have taken part in the new tests reported here, many providing updated results using the new data. In addition, further participants have also taken part, and we provide extra analysis of the retrieval results. A total of 25 different shape retrieval methods are compared.

In this paper, we propose a 2D approach for real-time animation of vegetation in 3D scenes, especially suitable for simulating wind effects on 3D vegetation fields with densely leaved foliage. We represent a vegetation field as view-dependent 2D billboard layers, perform a 2D harmonic motion simulation for modeling the dynamics of vegetation at the first layer (closest to the viewer), and utilize this dynamics to guide the animation of the rest of the layers while addressing the motion effects in depth and occlusion effects. As a result, our method can produce natural looking motions of vegetation swaying in wind comparable with existing commercial software, however the effort to setting up the underlying animation model and the computational cost can be significantly reduced.

Modern computer graphics applications commonly feature very large virtual environments and diverse characters which perform different kinds of motions. To accelerate path planning in such a scenario, we propose the subregion graph data structure. It consists of subregions, which are clusters of locally connected waypoints inside a region, as well as subregion connectivities. We also present a fast algorithm to automatically generate a subregion graph from an enhanced waypoint graph map representation, which also supports various motion types and can be created from large virtual environments. Nevertheless, a subregion graph can be generated from any graphbased map representation. Our experiments show that a subregion graph is very compact relative to the input waypoint graph. By firstly planning a subregion path, and then limiting waypoint-level planning to this subregion path, over 8 times average speedup can be achieved, while average length ratios remain as low as 102.5%.

We augment images with additional data allowing us to visualize them with elements of animation as well as interact with the images using haptic devices as if they were actual 3D scenes. First, we apply procedural simulation to simulate image distortions, which are characteristic for various phenomena like blowing wind, fluid flow, etc. Next, we consider how haptic rendering of images can be performed. This in turn includes haptic rendering of forces augmented to the images as well as haptic interaction with haptic objects augmented to the images. The immersive images thus obtained can be exchanged across the internet to realistically simulate 3D virtual scenes while in fact still be 2D images augmented with rather little additional data files in a way how movie subtitles files are added to the video files. The proposed approach is illustrated with a few representative examples.

In this paper, we propose a simple method to animate vegetation in images. The proposed method enables users to interactively animate vegetation in real-time. It can be used to enhance a vegetation photograph or painting with animated motions as well as to help animators to create cartoon animation of vegetation. Our method is suitable for simulating vegetation-wind interaction for a dense vegetation field which exhibit non-rigid property, especially in cartoon style images. In our method, wind field is modeled using fluid simulation. We adopt a harmonic oscillator based on wave simulation as the numerical model for the dynamics of vegetation. The velocity generated from the wind field is used to drive the wave simulation to determine the velocity of vegetation. Based on the velocity of vegetation, we employ a grid-based warping approach to animate different types of vegetation such as grass and trees. As a result, for vegetation in images, we can simulate grass and trees swaying in wind as well as under water plants swaying in water. Our method can produce natural-looking output motions comparable with real cartoons. Users can interactively control the location of the source, direction and strength of the wind or water flow and the property of vegetation on the fly.

In computer graphics, textures represent the detail appearance of the surface of objects, such as colors and patterns. Example-based texture synthesis is to construct a larger visual pattern from a small example texture image. In this paper, we present a simple and efficient method which can synthesize a large scale texture in real-time based on a given example texture by simply tiling and deforming the example texture. Different from most of the existing techniques, our method does not perform search operation and it can compute texture values at any given points (random access). In addition, our method requires small storage which is only to store one example texture. Our method is suitable for synthesizing irregular and near-stochastic texture. We also propose methods to efficiently synthesize and map 3D solid textures on 3D meshes.

Our research focuses on the problem of path planning, which often occurs in virtual world applications. We propose an automatic generation of enhanced waypoint graph, which is a graph data structure consisting of point nodes, which describe the corner features in the virtual world, as well as edges connecting those nodes. Given a polygon soup representation of a virtual world, for every character radius, the proposed algorithm starts by constructing a discrete distance field, consisting of regularly sampled points in 3D space. Corner detection and clustering are then done with respect to the points whose distance values are slightly larger than the character size to get the waypoints. These waypoints are further sparsely connected using traversability test, taking into account their distances to nearby obstacles. The resulting enhanced waypoint graph is sparse but has regularly distributed edges emanating from each waypoint. In addition, the graph is also able to handle different types of motions for characters with various sizes.

2D sketch-3D model alignment is important for many applications such as sketch-based 3D model retrieval, sketch-based 3D modeling as well as model-based vision and recognition. In this paper, we propose a 2D sketch-3D model alignment algorithm using view context and shape context matching. A sketch consists of a set of curves. A 3D model is typically a 3D triangle mesh. It includes two main steps: precomputation and actual alignment. In the precomputation, we extract the view context features of a set of sample views for a 3D model to be aligned. To speed up the precomputation, two computationally efficient and rotation-invariant features, Zernike moments and Fourier descriptors are used to represent a view. In the actual alignment, we prune most sample views which are dissimilar to the sketch very quickly based on their view context similarities. Finally, to find an approximate pose, we only compare the sketch with a very small portion (e.g. 5% in our experiments) of the sample views based on shape context matching. Experiments on two types of datasets show that the algorithm can align 2D sketches with 3D models approximately.

Simulating grass field in real-time has many applications, such as in virtual reality and games. Modeling accurate grass-grass, grass-object and grass-wind interactions requires a high computational cost. In this paper, we present a method to simulate grass field in real-time by considering grass field as a two dimensional grid-based continuum and shifting the complex interactions to the dynamics of continuum. We adopt the wave simulation as the numerical model for the dynamics of continuum which represents grass-grass interaction. We propose a procedural approach to handle grass-object and grass-wind interactions as external force that updates the wave simulation. The proposed method can be efficiently implemented on a GPU. As a result, massive amounts of grass can interact with moving objects and wind in real-time.

A lot of non-photorealistic rendering methods have been proposed for creating an artistic image from an image. In this paper, we propose a method for creating colored pencil style images. The feature of colored pencil drawings is that, though colored pencil drawings are drawn with limited number of colors of pencils, we can express a lot of colors and gentle textures by changing the strengths when drawing strokes and by overlapping strokes of different colors. In order to realize this feature, we determine which colors of pencils to use and how deep to push the pencils (equivalent to the strength when drawing strokes), then draw several types of strokes, such as strokes for outlines, basecoats, and shading, allowing the strokes to overlap each other. When we create strokes for shading, we make their directions to align along the boundaries of regions, resulting in images that are more like drawings made by human.

Abstract Environment illumination, which is a complex and distant lighting environment represented by images, is often applied to create photo‐realistic images. However, creating photo‐realistic animations under environment illumination is exceedingly compute intensive. The Precomputed Radiance Transfer (PRT) methods achieve real‐time rendering under environment illumination; however, these methods only have a limited application in animation because the objects in the scene cannot be moved or rotated. In this paper, we propose a method for rendering photo‐realistic animations of dynamic scenes under environment illumination in real time. We notice the fact that when objects are moved or rotated, changes of radiances occur mainly in the regions of shadows cast by other objects. Our method makes a distinction between self‐shadow and shadows cast by other objects and computes these two kinds of shadows efficiently. Copyright © 2005 John Wiley & Sons, Ltd.

The rapid growth in computer graphics and digital cameras has resulted in computer users being able to easily produce digital images. As a result, the need to display and print digital images has increased. Nowadays, high-resolution display and printing devices are available to users. Therefore, high-resolution images are needed in order to produce high quality displayed images and high quality prints. However, since high-re solution images are not usually provided, there is a need to magnify the original images. Previous methods on magnifying images have the disadvantage that either the sharpness of the edges cannot be preserved or that some distinct artifacts are produced in the magnified image. In this paper, we present a novel method for doubling the size of images in which the sharpness of the edges is preserved without introducing distinct artifacts in the magnified images. The proposed method consists of two steps, first generation of an initial magnified image and then progressively refining this image to produce a high quality magnified image. The experimental results show that with the proposed method it is possible to produce magnified images of comparable, and in some cases superior, visual quality to those produced using previous methods.

A number of nonphotorealistic rendering methods for producing artistic style images have been developed. Recently, a method called "Image Analogies" was proposed. This method is based on the idea of example-based filtering that uses a pair of images (an original image and a filtered image) as training data and creates an image which has a style that resembles the filtered image of the training data. This method has great flexibility since the users can create various styles of images by simply changing the training data. We extend "Image Analogies" to create various styles of animations. The coherence between frames is considered by computing the pixel flows between the frames. From experimental results, the proposed method can create nice animation sequences.

This paper presents a new method for smoothly blending among multiple polygonal shapes. The blended shape is computed as a weighted average of the input shapes. The weight of each input shape is allowed to vary across the shape. This feature increases the flexibility for controlling the local appearance of the blended shapes. Our method computes the blended shape hierarchically, starting from the coarse version of the shape and adding the details gradually. Several examples are shown to demonstrate the advantages of the proposed method.

This paper presents solutions to the feature correspondence and feature interpolation problems in image morphing. The user specifies the correspondence between the source and the target images by drawing input curves on the features of the objects. The correspondence between these curves at the finest level (pixel level) is computed by optimizing a cost function. Based on this correspondence, the input curves are approximated by using Bezier curves. We represent the Bezier curves and the connections among them by using a "dependency graph". Feature interpolation is performed by interpolating the dependency graphs using the edge-angle blending technique. We also propose methods for controlling the transition rates of the shape and the color. We implemented the proposed algorithms in our morphing system which is based on the field morphing technique. From experimental results, our algorithms can generate a smooth morphing animation even when the objects in the source and the target images have different orientations. Also, the user's workload is reduced because the system includes an automatic feature correspondence computation.

Parametric surfaces and implicit surfaces are generally used for representing curved surfaces in CAD/CG Systems. This paper discusses a curved tubular object which is a surface swept by a sphere/circle moving along a curve. For the trajectory curve, a 3D Bezier curve is employed, and its radius can be varied along the curve. In general, its surface cannot be defined by a closed form, while a high degree of polynomial must be solved for ray/surface intersection. This paper proposes an effective rendering method which uses a scan line algorithm for detecting curved tubular objects on the projection plane. The calculation of the distance from a point to a curve plays an important role in our algorithm. Bezier Clipping Method is employed for this calculation.