In biology, the morphometric analysis is widely used to analyze the inter-organisms variations. It allows to classify and to determine the evolution of an organism’s family. The morphometric methods consider features such as shape, structure, color, or size of the studied objects. In previous works [8], we have analyzed beetle mandibles by using the centroid as feature, in order to classify the beetles. We have shown that the Probabilistic Hough Transform (PHT) is an efficient unsupervised method to compute the centroid. This paper proposes a new approach to precisely estimate the landmark geometry, points of interest defined by biologists on the mandible contours. In order to automatically register the landmarks on different mandibles, we defined patches around manual landmarks of the reference image. Each patch is described by computing its SIFT descriptor. Considering a query image, we apply a registration step performed by an Iterative Principal Component Analysis which identify the rotation and translation parameters. Then, the patches in the query image are identified and the SIFT descriptors computed. The biologists have collected 293 beetles to provide two sets of mandible images separated into left and right side. The experiments show that, depending on the position of the landmarks on the mandible contour, the performance can go up to 98% of good detection. The complete workflow is implemented in the MAELab framework, freely available as library on GitHub.
It is well known that multi-sensory stimulation can enhance immersion within virtual environments. Whilst there has been rapid development of devices which can enhance the visual immersion, technology to stimulate other senses, such as touch, is still under developed. Currently there is a problem wherein a surface in a virtual environment, such as a wall, cannot replicate the physical properties of a solid object. In this paper a novel system is proposed utilising the HTC VIVE and Rethink Robotics' Baxter Robot to replicate surfaces. A demonstration has been created whereby a user climbs a wall in a virtual environment by grabbing onto ledges which exist as a physical body located on Baxter's end effector. The system uses bi-directional TCP communication between an environment developed in Epic Games' Unreal Engine and the Baxter robot running the Robot Operating System framework. When an ascending user reaches out and grabs a ledge on the virtual wall they will be applying a torque to the Baxter arm which can be measured and the intended movement of the user inferred, resulting in the ledge being moved through a suitable Inverse Kinematics path. This has provided the user with the ability to climb a wall in VR in the absence of any hand tracking methods whilst receiving force feedback from the ledges they grasp onto. Current alternative systems only exist as wearables or operate in small spaces. The increased immersion in this VR demo can be used to assist those with phobias of heights.
With the release of various low cost consumer head mounted displays, such as the HTC Vive, virtual reality (VR) visualisation technology is becoming common place. However, haptic interactions continue to lag behind the visual developments. Touch feedback from the HTC Vive system is only provided by way of vibrations in the physical controllers. There are currently no large scale haptic devices that allow a user to experience force feedback in a room scale VR environment. The research presented in this paper demonstrates this problem can be addressed through the use of a large robotic arm to create an encounter haptic solution. Our haptic VR system uses the HTC Vive and the Baxter robot. Positional data is taken from the Vive controllers and sent to one of the Baxter's 7 degrees of freedom arms, which is used to provide force feedback to the user. An experiment was created where a user pushes wooden boxes off a wall in a VR environment. Several tests were performed. Different virtual boxes with a different simulated weight were simulated by varying the speed at which the Baxter moves away from the user. Results from a thirty participant user study indicate that desirable haptic effects can be achieved in a large room scale environment.
This paper presents an efficient algorithm for a global parameterization of triangular surface meshes. In contrast to previous techniques which achieve global parameterization through the optimization of non-linear systems of equations, our algorithm is solely based on solving at most two linear equation systems, in the least square sense. Therefore, in terms of running time the unfolding procedure is highly efficient. Our approach is direct – it solves for the planar UV coordinates of each vertex directly – hence avoiding any numerically challenging planar reconstruction in a post-process. This results in a robust unfolding algorithm. Curvature prescription for user-provided cone singularities can either be specified manually, or suggested automatically by our approach. Experiments on a variety of surface meshes demonstrate the runtime efficiency of our algorithm and the quality of its unfolding. To demonstrate the utility and versatility of our approach, we apply it to seamless texturing. The proposed algorithm is computationally efficient, robust and results in a parameterization with acceptable metric distortion.
Image deformation technique is widely used in the field of computer animation, image editing, medical imaging, and other applications in 2D and 3D computer graphics. All the algorithms aim to provide simple user interface, most of which need the user to drag the control points, lines or polygon. The deformation process and the final position of the controlling points should be smooth and precise respectively, and it should also run in real-time.This paper provides a simple image deformation method using the radial basis function interpolation in approximation theory. Radial basis function is a very popular and convenient tool for data representation problems. The proposed method using radial basis function is fast and easy to use more than previous deformation methods. Experiments indicate that the algorithm is stable and well performed.
This study improves the ergonomics of using the Leap Motion hand tracking device with an Oculus Rift. The improvements were realised through the use of a 3D printed mount that angled the Leap Motion down by 30 degrees. This allowed for users to interact with a virtual environment in which their arms may be held in a biomechanically less stressful location, rather than up and in front of their face. To validate the configuration, 15 participants completed a specially designed task which involved pressing virtual buttons in a given location. The button pressing task was performed in three configurations that compared the angled mount against the standard forward facing mount. Results indicate that the angled mount eliminates tracking loses, whilst producing comparable accuracy against the control condition and allowing the participant to interact in a more natural arm posture.
Ray tracing is one of the most important rendering techniques in computer graphics. By means of simulating reflection and refraction of light transportation, ray tracing generates more photorealistic images than scanline rendering. However, the high computational cost is the main disadvantage of ray tracing algorithm. In recent years, the computing power of GPU has increased dramatically, and general-purpose computing on graphics processing units (GPGPU) has become popular. Many scholars have presented some physically based rendering methods with CUDA or OpenCL in order to improve image quality and increase rendering speed. Because rasterization is the mainstream in the gaming industry, there is still a long way to go to make ray tracing accepted by the industry in the near future. We introduce a ray tracing API integration for OpenGL applications that can replace the original OpenGL rasterization with ray tracing by simply adding a few lines of code, and the ray tracing algorithm in this API is parallelized by OpenCL.
Layered Depth Images (LDI) compactly represent multiview images and videos and have widespread usage in image-based rendering applications. In its typical use case scenario of representing a scanned environment, it has proven to be a less costly alternative than separate viewpoint encoding. However, higher quality laser scanner hardware and different user interaction paradigms have emerged, creating scenarios where traditional LDIs have considerably lower efficacy. Wide-baseline setups create surfaces aligned to the viewing rays producing a greater amount of sparsely populated layers. Free viewpoint visualization suffers from the variant quantization of depths on the LDI algorithm, reducing resolution of the dataset in uneven directions. This paper presents an alternative representation to the LDI, in which each layer of data is positioned in different viewpoints that coincide with the original scanning viewpoints. A redundancy removal algorithm based on world-space distances as opposed to to image-space is discussed, ensuring points are evenly distributed and are not viewpoint dependent. We compared our proposed representation with traditional LDIs and viewpoint dependent encoding. Results showed the multiview LDI (MVLDI) creates a smaller number of layers and removes higher amounts of redundancy than traditional LDIs, ensuring no relevant portion of data is discarded in wider baseline setups.
Most virtual globe systems feature a rendering of the atmosphere that surrounds the earth. This element is so widespread that seeing a virtual earth without a surrounding halo makes the image seem much more artificial. Atmospheric rendering is a costly process aimed to enhance the realism and beauty of the scene. For that reason many virtual globe systems, specially in low-resourced devices, rely on simplified schemes to represent the atmosphere. However, the accurate representation of the atmosphere implies the volumetric rendering of the semi-transparent air mass that covers the whole geographical scene. Thus, the color of each pixel is composed of the light scattered by all the points in space projected on that pixel. The present work takes advantage of the spherical symmetry of the atmosphere's mathematical model to implement efficiently this volumetric rendering on mobile devices.
Nowadays, large volumes of terrain data are available to use as Digital Elevation Models, from which coarser meshes can be progressively generated for visualization and other purposes. Previous studies compared different methods to adjust those meshes, concluding that no method performs the best for all kinds of terrain. In this work, a pipeline to accurately adjust TRNs to DEM is proposed. An initial approximation is calculated by solving a linear system from input data. Vertices with a major contribution to the global error of the mesh are then tuned using a local refinement algorithm. Experimentation shows that meshes adjusted using the proposed pipeline fit better the original DEM than ones generated using classic methods as linear interpolation for several benchmark elevation models.
Using anti-aliased signed distance fields for generating surgical guides and plates from CT images
3D modeling for Archaeology requires to easily model scenes by letting users evaluate a parametric specification of archaeology-oriented gestures, then modify and reevaluate the specification to produce various restitution hypotheses. But the current modeling tools that support reevaluation mechanisms are not dedicated to Archaeology. The Jerboa library, based on graph transformations rules, is well suited for creating operations fitting the needs of archaeologists. But it does not any support reevaluation mechanism and especially the persistent naming system, that is used to identify the entities of the initial model and match them with entities of the reevaluated model. In this paper, we extend Jerboa with a new application-independent persistent naming model, which is more general and homogeneous than other solutions found in the literature and is the first one to handle parametric specification edition.
Detecting corner locations in images plays a significant role in several computer vision applications. Among the different approaches to corner detection, contour-based techniques are specifically interesting as they rely on edges detected from an image, and for such corner detectors, edge detection is the first step. Almost all the contour-based corner detectors proposed in the last few years use the Canny edge detector. There is no comparative study that explores the effect of using different edge detection method on the performance of these corner detectors. This paper fills that gap by carrying out a performance analysis of different contour-based corner detectors when using different edge detectors. We studied four recently developed corner detectors, which are considered as current state of the art and found that the Canny edge detector should not be taken as a default choice and in fact the choice of edge detector can have a profound effect on the corner detection performance. We examined commonly used predefined threshold-based Canny detector with the adaptive Canny detector and found that adaptive Canny detector gives better results to work with.
We propose using Immersive Virtual Reality activities to improve the spatial ability of engineering students based on the study of solid geometry. The work group is selected randomly from among all the students registered for the 1st term course Graphic Expression and Computer-Aided Design (GECAD) at the Barcelona College of Industrial Engineering (EUETIB). A total of 60 participants completed three activities (6 h) in VR, using head-mounted display (HMD) glasses. Another group of students (30) made up the control group, which carried out only the learning activities that were common to all students, in a SolidWorks 3D non-immersive solid modeling software environment. Spatial abilities are assessed using the Differential Aptitude Test: Spatial Relations Subset (DAT:SR) and the Purdue Spatial Visualization Test: Rotations (PSVT:R). Previous studies have demonstrated a close correlation between successful comprehension of the Graphic Engineering course contents and high scores on the DAT:SR test. The greatest correlation was found between the DAT:SR pre-test and the solid geometry exam (test and 3D modeling exercises). We propose measuring spatial abilities before and after the classroom activities and looking for correlations between the spatial perception tests (DAT:SR and PSVT:R) and academic results in solid geometry. Furthermore, we also wish to determine the students' opinion with regard to the proposed activities. This would permit us to recommend and incorporate the use of VR in order to improve spatial abilities, in particular for those students with lower levels of spatial abilities, as measured by a DAT:SR or PSVT:R.
Since a fisheye lens can capture a wide angle scenery, it is broadly used for surveillance or outdoor sports. However, acquired images suffer from severe geometric distortions. Most of the existing distortion correction algorithms depend on linear features: images of linear features are first identified and then 2 dimensional warping is applied to make the curved images look straight. We propose a novel fisheye distortion correction method that estimates 3 dimensional (3D) locations of a foreground first, and then projects them to an image plane by perspective projection. When we know approximate distance of the foreground object, as in cases of head mounted camera, we can assume the 3D object plane of the foreground, and then estimate the 3D location from image points after internal camera calibration. For head mounted camera, foreground is a face and body of a human, and distortion of human figure is quite unnatural and awkward. Moreover, human figures lack linear features which excludes the use of conventional 2D warping techniques. We present techniques to estimate the 3D position from a corresponding 2D image point, which enables calculation of 3D object location. And then apply perspective projection to the 3D object position to obtain a distortion-free image. We demonstrate the efficacy of the proposed method using fisheye camera images and the applicability of the proposed concept to real applications.
Skin is one of the most difficult materials to reproduce in computer graphics, mainly due to two major factors: First, the complexity of the light interactions happening at the subsurface layers of skin, and second, the high sensitivity of our perceptual system to the artificial imperfections commonly appearing in synthetic skin models. Many current approaches mix physically-based algorithms with image-based improvements to achieve realistic skin rendering in realtime. Unfortunately, those algorithms still suffer from artifacts such as halos or incorrect diffusion. Some of these artifacts (e.g. incorrect diffusion) are especially noticeable if the models have not been previously segmented. In this paper we present some extensions to the Separable Subsurface Scattering (SSSS) framework that reduce those artifacts while still maintaining a high framerate. The result is an improved algorithm that achieves high quality rendering for models directly obtained from scanners, not requiring further processing.
This paper presents a graphics processing unit (GPU) implementation of a recently published augmented Lagrangian based L 1 -mean curvature image denoising algorithm. The algorithm uses a particular alternating direction method of multipliers to reduce the related saddle-point problem to an iterative sequence of four simpler minimization problems. Two of these subproblems do not contain the derivatives of the unknown variables and can therefore be solved point-wise without inter-process communication. In particular, this facilitates the efficient solution of the subproblem that deals with the non-convex term in the original objective function by modern GPUs. The two remaining subproblems are solved using the conjugate gradient method and a partial solution variant of the cyclic reduction method, both of which can be implemented relatively efficiently on GPUs. The numerical results indicate up to 33-fold speedups when compared against a single-threaded CPU implementation. The pointwise treated subproblem that takes care of the non-convex term in the original objective function was solved up to 76 times faster.
We present an improvement of a unified topological-physical model which permits topological modifications during physical simulation of soft tissues. Our improvement makes the model more generic, efficient and simpler to update. The main principle of our improvement is to associate information to elements of the model, depending on the underlying physical model. Our modification of the architecture enables to easily integrate different physical models. Moreover, topological operations and physical simulations can be factorized between the different physical models. Our solution is more efficient as it leads to simpler modification algorithms after topological alterations with less changes to apply. In this paper, we present our new solution and illustrate its new properties thanks to several experiments performed on two well-known physical models: Mass-Spring System and Tensor-Mass model. The results present a comparison of our solution with the previous one for the cutting topological operation. Moreover, as our model permits to easily compare several physical models, we performed some simulations to reproduce experiments made on real tissues.
This paper presents an extension system to a closed-source, real-time physics engine for improving structured stacking behavior with small-scale objects such as wooden toy bricks. The proposed system was implemented and evaluated. The tests showed that the system is able to simulate several common stacking scenarios, which the base physics engine cannot simulate.
Semi-automatic segmentation of the prostate boundary is presented for the pre-operational images of the MRIguided ultrasonic thermal therapy of the prostate cancer. The specific deformable surface method is based on firstly fitting an ellipsoid on the given manual landmark points, then modifying the shape of the initialization surface mesh by masking out the regions of the separately segmented bladder and rectum, and finally adapting the surface mesh by searching image for the edge boundaries in the direction of the surface normal. The suggested segmentation method combines information from two types of pre-operational MR-images showing different contrast for the tissue structure. Dice similarity coefficient (DSC) between the semi-automatic segmentation and the manual reference was on average 0.89 for a group of N=5 patients having the MRI guided ultrasound thermal treatment. The robustness of the surface fitting method was tested by simulating 30 randomized initialization sets of the landmark points for each patient, and the resulting standard deviation of DSC was 0.01.
