Perspective Projection Research Articles

Automatic Unfolding of CityGML Buildings to Paper Models

3D city models are mainly viewed on computer screens, but many municipalities also use 3D printing to make urban planning tangible. Since 3D color printing is still comparatively expensive and the colors often fade over time, many of these models are monochrome. Here, color textured paper models offer an inexpensive and under-appreciated alternative. In this paper, a greedy algorithm adapted to CityGML building models is presented, which creates print templates for such paper models. These 2D layouts consist of cut edges and fold edges that bound polygons of a building. The polygons can be textured or left blank depending on the existence of CityGML textures. Glue tabs are attached to cut edges. In addition to the haptic 3D visualization, the quality of the 3D models can sometimes be better assessed on the basis of the print templates than from a perspective projection. The unfolding procedure was applied to parts of the freely available CityGML model of Berlin as well as to parts of models of the cities of Dortmund and Krefeld.

A Post-Scan Point Cloud Colorization Method for Cultural Heritage Documentation

The 3D laser scanning technique is important for cultural heritage documentation. The laser itself normally does not carry any color information, so it usually requires an embedded camera system to colorize the point cloud. However, when the embedded camera system fails to perform properly under some external interferences, a post-scan colorization method is always desired to improve the point cloud visuality. This paper presents a simple but efficient point cloud colorization method based on a point-to-pixel orthogonal projection under an assumption that the orthogonal and perspective projections can produce similar effects for a planar feature as long as the target-to-camera distance is relatively short (within several meters). This assumption was verified by a simulation experiment, and the results show that only approximately 5% of colorization error was found at a target-to-camera distance of 3 m. The method was further verified with two real datasets collected for the cultural heritage documentation. The results showed that the visuality of the point clouds for two giant historical buildings had been greatly improved after applying the proposed method.

An optimization measurement method of laser sensor based on perspective projection model

Perspective projection model is the common measurement method for laser sensor to calculate the 3D coordinates of spatial points. However, the error of mathematical model is introduced, which inevitably decrease the measurement accuracy of laser sensor. In order to improve the accuracy, an optimization measurement method is proposed in this paper. Firstly, the structural design and measurement principle of laser sensor is developed. Secondly, the error propagation model is established, and the effect of the structural parameters in perspective projection model is probed in detail. Next, an optimization measurement method is presented by adjusting the structural parameters, which is the projection angle of laser beam in measurement coordinate system. Finally, the effectiveness of the proposed optimization method is evaluated by the simulative and practical experiments. The experiment results show that the maximum error can be reduced to 0.589 mm with optimization from 1.090 mm of previous method. Enough theoretical research is offered for optimization design of measurement model of the laser sensor.

Lunar Crater Identification in Digital Images

It is often necessary to identify a pattern of observed craters in a single image of the lunar surface and without any prior knowledge of the camera’s location. This so-called “lost-in-space” crater identification problem is common in both crater-based terrain relative navigation (TRN) and in automatic registration of scientific imagery. Past work on crater identification has largely been based on heuristic schemes, with poor performance outside of a narrowly defined operating regime (e.g., nadir pointing images, small search areas). This work provides the first mathematically rigorous treatment of the general crater identification problem. It is shown when it is (and when it is not) possible to recognize a pattern of elliptical crater rims in an image formed by perspective projection. For the cases when it is possible to recognize a pattern, descriptors are developed using invariant theory that provably capture all of the viewpoint invariant information. These descriptors may be pre-computed for known crater patterns and placed in a searchable index for fast recognition. New techniques are also developed for computing pose from crater rim observations and for evaluating crater rim correspondences. These techniques are demonstrated on both synthetic and real images.

Automatic tracking of healthy joint kinematics from stereo-radiography sequences

Kinematic tracking of healthy joints in radiography sequences is frequently performed by maximizing similarities between computed perspective projections of 3D computer models and corresponding objects’ appearances in radiographic images. Significant human effort associated with manual tracking presents a major bottleneck in biomechanics research methods and limits the scale of target applications. The current work introduces a method for fully-automatic tracking of tibiofemoral and patellofemoral kinematics in stereo-radiography sequences for subjects performing dynamic activities. The proposed method involves the application of convolutional neural networks for annotating radiographs and a multi-stage optimization pipeline for estimating bone pose based on information provided by neural net predictions. Predicted kinematics are evaluated by comparing against manually-tracked trends across 20 distinct trials. Median absolute differences below 1.5 millimeters or degrees for 6 tibiofemoral and 3 patellofemoral degrees of freedom demonstrate the utility of our approach, which improves upon previous semi-automatic methods by enabling end-to-end automation. Implementation of a fully-automatic pipeline for kinematic tracking will benefit evaluation of human movement by enabling large-scale studies of healthy knee kinematics.

PROJECT MANAGEMENT COMPETENCE DEVELOPMENT IN APPLICANTS FOR PHD PROGRAMS

The article is devoted to the issues of applicants’ preparation for higher education at the third educational and scientific level of higher education, speciality 231 Social work. 
 In the research, based on normative documents, the necessity of project activity competencies development of future applicants of educational and scientific programs has been substantiated. It has been proved the importance of development in the new generation of future managers knowledge and skills to use a modern project approach to solving problems of management processes at different levels. Mastering project management methodology is a new progressive toolkit for social work management as a probable field of activity of PhD graduates in 231 Social Work. Possibilities of information work in project activity are opened, in particular search of information on grant offers, competitions of perspective projects and archival data on already realized. The Group Resource Center was presented as a leading national centre of public information and expertise, which is aimed at the development of civil society and the development of Ukraine. As well as the Public Space portal, which offers unique and up-to-date information on the development of civil society in Ukraine, provides an opportunity to be involved in public activities and important transformations in the country. 
 The article highlights and substantiates the feasibility of certain theoretical and practical recommendations for the formation of project skills of the future Doctor of Philosophy in social work, including achieving a level of unconscious competence in the development of project proposals, use of democratic governance tools in project activities, effective search, analysis and use of grant information, proposals, mastering the strategy and tactics of team project activities.

Promising manned spacecraft for a long-duration flight with a flexible inflatable shell

The development of astronautics is approaching the stage of colonization of space objects of the Solar System, which will lead to regular and long-term manned space flights. Perspective projects of colonization and long-term stay of a man in space flight conditions were considered. The project proposed in this article is based on a conceptual approach. This paper considers the new type of promising spacecraft that solve the problem of the influence of the absence of gravity on a person in space during a long flight. The principle of a new generation manned spacecraft (MS) is presented. Using a flexible inflatable shell is a solution to reduce the mass of the MS. The analysis of existing solutions of flexible inflatable shells of American and Russian analogues and for the developed design of a new generation spacecraft is carried out. The comparison of the characteristics of three types of shells is made, with the definition of general and distinctive features of the structure and the system that provides the deployment of shells. Advantages and disadvantages of projects are described.

Three-dimensional videography using omnidirectional cameras: An approach inspired by the direct linear transformation method

Direct linear transformation (DLT) is one of the most frequently used methods in motion analysis. This method was developed in 1971 and has subsequently been used in numerous studies. However, owing to the structure of the camera, unfavorable challenges are associated with this method. Because the DLT method is based on the structure of ordinary optical cameras in which the perspective projection is used, the camera’s angle of view is limited. In this study, we propose a three-dimensional (3-D) calibration and reconstruction method using omnidirectional cameras, which have significantly wider angles of view than conventional cameras. For the interest points, the longitude and latitude of the celestial sphere are obtained from the image captured with an omnidirectional camera. The direction of the interest points relative to the camera’s reference frame is determined via the longitude and latitude. In the calibration phase, the position and orientation of the omnidirectional camera relative to the global reference frame are determined from the image of the control points with known 3-D coordinates. In the reconstruction phase, the intersection point of the rays from the cameras is determined. Using an evaluation experiment, we verified the accuracy of the proposed method. The wide angle of view provided by omnidirectional cameras can be fully exploited using this method.

Three Points of View for the Drawing Adoration of the Magi by Leonardo da Vinci

This contribution to the literature presents an in-depth analysis of the scene drawn by Leonardo da Vinci in the preparatory drawing, Adoration of the Magi, dated 1481, that is now housed at the Département des Arts Graphiques du Musée du Louvre in Paris, France. This analysis focuses on the architectural elements and highlights how the drawing discloses three distinct vanishing points/centers of vision: one for the classical architecture to the left of the scene, one for the Nativity hut, and one for the structure with stairs. If we consider the structures as belonging to the same 2D projected space, at least two must be depicted out of square; conversely, if we consider them as straight, standard structures, they cannot belong to the same 2D projected space. Given this assumption, we propose, on the one hand, some variations of the scene where the structures are straightened and projected according to only one of the viewpoints at a time; on the other hand, a set of variants of the scene are presented, considering the out-of-square structures. The scenes are generated by applying inverse perspective projections. These results prompt a discussion on possible reasons why Leonardo made these conscious or unconscious “formal errors”.

Intelligent Three-Dimensional Reconstruction Algorithm-Based X-Ray Film for Analysis of the Changes in Sagittal Parameters and Curative Effect of Anterior Cervical Surgery

In this paper, the change characteristics of sagittal parameters of the patient’s body before and after anterior cervical surgery and rehabilitation effect were analyzed. The rotation transformation and perspective projection transformation were applied to construct a positive and lateral position (PLP) matching-based three-dimensional reconstruction (PLP-3DR) algorithm, which was compared with the marching cubes (MC) algorithm and gravity point (GP) algorithm. PLP-3DR was adopted in X-ray image diagnosis of 124 cervical spondylosis patients. Results showed that sensitivity, specificity, and accuracy of PLP-3DR were markedly higher than those of MC and GP ( P < 0.05 ). The postoperative C2-7 Cobbs’s angle (C2-7Cobb) (11.27 ± 8.41°) was smaller than that before the surgery (15.03 ± 7.39°) ( P < 0.05 ), while the postoperative cervical sagittal vertical axis (cSVA) (21.33 ± 10.38 mm) and Japanese Orthopaedic Association (JOA) scores (16.95 ± 6.07 points) were greater than those before the surgery (14.66 ± 9.68 mm and 11.39 ± 4.28 points) ( P < 0.05 ). Besides, the improvement rate of patients from the cSVA >25 mm group (68.31%) was greater than the rate of the cSVA <15 mm group (45.88%) and the cSVA within 15–25 mm group (47.29%) ( P < 0.05 ). In conclusion, PLP-3DR could effectively improve the diagnostic effect of spine X-ray film images, with high sensitivity and specificity. Anterior cervical surgery had a good curative effect for patients with cervical spondylosis and was closely related to cervical parameters (cSVA, T1 slope, and C2-7Cobb). In addition, patients with cSVA>25 mm could have the best postoperative rehabilitation effect.

Breast cancer grade identification using molecular imaging with Chitosan nanoparticles through SEM images

In this paper, Breast cancer cells grade identify through molecular imaging with chitosan nanoparticles. Breast cancer images with chitosan nanoparticles acquired through SEM camera. However, traditional method of imaging such as CT, Mammogram, and MRI never classifies the cancer grade and never detect cancer cells below 5 mm. The proposed TDyWT based image enhancement of SEM images enhances cancer cells through perspective projection. The perspective projection in cancer cell image enhances cells below 5 mm, preserves boundary, curvature and eliminates cancerous and non cancerous mixed pixels. Furthermore, TDyWT processed image apply with the GLCM parameters for grade classification of cancer cells. From simulation results, proposed TDyWT performs better than traditional algorithms such as DWT and SWT in terms of better visual interpretational and statically parameters.

Visualization of dentate nucleus, pontine tegmentum, pontine nuclei from CT image via nonlinear perspective projection

Visualization of dentate nucleus, pontine tegmentum, pontine nuclei from CT image via nonlinear perspective projection

Shape from apparent contours for bent pipes with constant diameter under perspective projection

In perspective projection images, apparent contours are important bases for recovering the three-dimensional (3D) shapes of constant diameter pipes (CDP). In order to complete the 3D reconstruction of CDP under perspective projection, this article first analyzes the single-view perspective projection model of CDP in detail. On this basis, coupled point pairs searching and projected axis extraction methods based on two facing apparent contours are proposed. After that, stereo vision technology is adopted to realize the 3D reconstruction of axis and the measurement of radius. Finally, the experiments with both synthetic and real data show that the proposed method has higher CDP reconstruction accuracy compared with the conventional method processed under orthogonal projection.

Visualization of Pterygomaxillary Fissure Structure and Shape in CT Image via Non-Linear Perspective Projection

The neurologist analyses the brain images to diagnose disease via structure and shape of the part in scanned Medical images such as CT, MRI, and PET. The Medical image segmentation performs less in the regions where no or little contrast, artifacts over the different boundary regions. The manual process of segmentation shows poor boundary differentiation due to discernibility in shape and location, intra and inter observer reliability. In this paper, we propose dyadic CAT optimization (DCO) algorithm to segment the regions in the brain from CT and MRI image via Non-linear perspective Foreground and Back Ground projection. The DCO algorithm removes the artifacts in the boundary regions and provide the exact structure and shape of the brain regions. The DCO algorithm shows the region boundary for pterygomaxillary fissure, occipital lobe, vaginal process zygomatic arch, maxilla and piriform aperture in brain image with high visibility in the regions of inadequately visible boundary and distinguishes the deformable shape. The DCO algorithm applies on 50 images and eight images with complex bone and muscle mass structure for performance evaluation. The DCO algorithm shows the increased Structural similarity index (SSIM) with 90% accuracy.

3D vibrations reconstruction with only one camera

In this paper, we propose a new method to measure the vibrations of a 3D mechanical structure. It requires only a video sequence taken by a single camera and a Finite Element model of the structure. First, the intrinsic and extrinsic parameters of the camera are identified. Then, a collection of numerical deflection shapes and normal modes are projected in the image frame of the camera. This is done thanks to a linearization of the perspective projection model. Comparing the motion of targets seen by the camera and the motion of Finite Element model at the same location gives the time evolution of modes amplitude. Finally the motion of the model is reconstructed in 2D in the image frame and in 3D in the world frame. By following this procedure, vibration amplitude can be magnified applying a scale factor on a modal basis covering a large frequency bandwidth.

An improved projector calibration method for structured-light 3D measurement systems

In a structured-light three-dimensional measurement system, understanding the optical configuration of the projector and suppressing the eccentricity error caused by the camera perspective projection are critical to realize high-precision measurement. In this paper, we analyze the special offset optical structure in commercial projectors, where a larger diameter lens is used to ensure the quality of the projected image, and the position of the principal point has been shifted. Meanwhile, a projector calibration strategy that makes the camera’s optical axis perpendicular to the target plane is proposed to avoid the pollution of perspective projection distortion. The sub-pixel correspondence based on homography transformation is performed by relying on the phase value of the fringe, and bundle adjustment optimization is used to further improve the accuracy and robustness of projector calibration. The experimental results demonstrate that the proposed calibration method can improve the calibration accuracy by 52.52%.

Fisheye Image Correction Based on Three-Dimensional Control Field

The fisheye image has severe distortions, which is not in line with human visual habits and brings inconvenience to its application. This paper classifies them into spherical structural distortion and optical distortion, and proposes a fisheye image correction method based on 3D control field. First, the spherical transformation radius and the optical center of the fisheye image are accurately solved, and the fisheye image is corrected by combining the spherical perspective projection; then, the distortion model of the fisheye camera is introduced into the DLT model to calibrate the optical distortion, and the results are used to recorrect the image. This method has been experimentally proven to be fast and effective.

Automatic Detection of Fiducial Landmarks Toward the Development of an Application for Digitizing the Locations of EEG Electrodes: Occipital Structure Sensor-Based Work.

The reconstruction of electrophysiological sources within the brain is sensitive to the constructed head model, which depends on the positioning accuracy of anatomical landmarks known as fiducials. In this work, we propose an algorithm for the automatic detection of fiducial landmarks of EEG electrodes on the 3D human head model. Our proposal combines a dimensional reduction approach with a perspective projection from 3D to 2D object space; the eye and ear automatic detection in a 2D face image by two cascades of classifiers and geometric transformations to obtain 3D spatial coordinates of the landmarks and to generate the head coordinate system, This is accomplished by considering the characteristics of the scanner information. Capturing the 3D model of the head is done with Occipital Inc. ST01 structure sensor and the implementation of our algorithm was carried out on MATLAB R2018b using the Computer Vision Toolbox and the FieldTrip Toolbox. The experimental results were aimed at recursively exploring the efficacy of the facial feature detectors as a function of the projection angle; they show that robust results are obtained in terms of false acceptance rate. Our proposal is an initial step of an approach for the automatic digitization of electrode locations. The experimental results demonstrate that the proposed method detects anatomical facial landmarks automatically, accurately, and rapidly.

Fixed-Lens camera setup and calibrated image registration for multifocus multiview 3D reconstruction

Image-based 3D reconstruction or 3D photogrammetry of small-scale objects including insects and biological specimens is challenging due to the use of a high magnification lens with inherently limited depth of field, and the object’s fine structures. Therefore, the traditional 3D reconstruction techniques cannot be applied without additional image preprocessing. One such preprocessing technique is multifocus stacking/fusion that combines a set of partially focused images captured at different distances from the same viewing angle to create a single in-focus image. We found that the image formation is not properly considered by the traditional multifocus image capture and stacking techniques. The resulting in-focus images contain artifacts that violate the perspective projection. A 3D reconstruction using such images often fails to produce accurate 3D models of the captured objects. This paper shows how this problem can be solved effectively by a new multifocus multiview 3D reconstruction procedure which includes a new Fixed-Lens multifocus image capture and a calibrated image registration technique using analytic homography transformation. The experimental results using the real and synthetic images demonstrate the effectiveness of the proposed solutions by showing that both the fixed-lens image capture and multifocus stacking with calibrated image alignment significantly reduce the errors in the camera poses and produce more complete 3D reconstructed models as compared with those by the conventional moving lens image capture and multifocus stacking.

Simulating virtual images in optical trap displays

Optical trap displays (OTD) are an emerging display technology with the ability to create full-color images in air. Like all volumetric displays, OTDs lack the ability to show virtual images. However, in this paper we show that it is possible to instead simulate virtual images by employing a time-varying perspective projection backdrop.