Perspective Projection

BACKGROUND—Software Process Improvement (SPI) is a systematic approach to increase the efficiency and effectiveness of a software development organization and to enhance software products. OBJECTIVE—This paper aims to identify and characterize evaluation strategies and measurements used to assess the impact of different SPI initiatives. METHOD—The systematic literature review includes 148 papers published between 1991 and 2008. The selected papers were

I ntroduction In his now classic book on Flatland, Edwin Abbott [1] describes the social order resulting in a world restricted to two spatial dimensions. The inhabitants of this world are completely unable to visualize a third spatial dimension and are therefore thoroughly baffled by the ...

In Portugal, the Perspectiva pictorum et architectorum (1693), by Andrea Pozzo, is shed both into scientific systematizations by Inácio Viera (1716), stating perspective principals and apparatus applied to the deception of the eye, along with the development of architectural illusions such as the Quadratura painted by Gonçalves Sena (1754), at Santarém’s Jesuit College, that openly asserts the pictorial resources of spatial visual manipulation.
This article observes technical and formal strategies undertaken by Sena, whose work is consequent to: reatise circulation among the city’s elite (producing a Portuguese translation); local imagery demands (after the departure of Simões Ribeiro who introduced and mastered the local quadraturist production); assimilation of Pozzo’s aesthetic and technical model (via the roman treatise); or by request of the Ignatian community (materializing an imagery program coincident with the one implemented by Pozzo at the Collegio Romano church).

BACKGROUND-Software Process Improvement (SPI) is a systematic approach to increase the efficiency and effectiveness of a software development organization and to enhance software products. OBJECTIVE-This paper aims to identify and characterize evaluation strategies and measurements used to assess the impact of different SPI initiatives. METHOD-The systematic literature review includes 148 papers published between 1991 and 2008. The selected papers were classified according to SPI initiative, applied evaluation strategies, and measurement perspectives. Potential confounding factors interfering with the evaluation of the improvement effort were assessed. RESULTS-Seven distinct evaluation strategies were identified, wherein the most common one, “Pre-Post Comparison,” was applied in 49 percent of the inspected papers. Quality was the most measured attribute (62 percent), followed by Cost (41 percent), and Schedule (18 percent). Looking at measurement perspectives, “Project” represents the majority with 66 percent. CONCLUSION-The evaluation validity of SPI initiatives is challenged by the scarce consideration of potential confounding factors, particularly given that “Pre-Post Comparison” was identified as the most common evaluation strategy, and the inaccurate descriptions of the evaluation context. Measurements to assess the short and mid-term impact of SPI initiatives prevail, whereas long-term measurements in terms of customer satisfaction and return on investment tend to be less used.

In this paper, we present a novel method to create parallax-free panoramic X-ray images of long bones during surgery by making the C-arm rotate around its X-ray source, relative to the patient’s table. In order to ensure that the C-arm motion is a relative pure rotation around its X-ray source, we move the table to compensate for the translational part of the motion based on C-arm pose estimation, for which we employed a Camera Augmented Mobile C-arm system [1] and a visual planar marker pattern. Thus, we are able to produce a parallax-free panoramic X-ray image that preserves the property of linear perspective projection. We additionally implement a method to reduce the error caused by varying intrinsic parameters of C-arm X-ray imaging. The results show that our proposed method can generate a parallax-free panoramic X-ray image, independent of the configuration of bone structures and without the requirement of a fronto-parallel setup or any overlap in the X-ray images. The resulting panoramic images have a negligible difference (below 2 pixels) in the overlap between two consecutive individual X-ray images and have a high visual quality, which promises suitability for intra-operative clinical applications in orthopedic and trauma surgery.

Voxel-based 2D/3D registration enables the use of preoperative 3D CT scans during X-ray fluoroscopy guided interventions for navigation purposes. Both a high accuracy and a short computation time are crucial. The method used in this project is described. Most time consuming is the computation of a perspective projection from the 3D data. Several volume visualisation methods to compute such a projection quickly and accurately are compared. The advantages and disadvantages of the methods in regard to our problem are discussed. Direct volume rendering methods proved to be particularly suitable and two specific methods were evaluated using a clinical dataset. Several optimisations of these methods in regard to 2D/3D registration are discussed and the results of two appropriate optimisations on the test dataset are shown. A recently proposed method based on a shear-warp factorisation of the viewing transformation combined with runlength encoded data showed the best results.

The fast radial symmetry (FRS) transform has been very popular for detecting interest points based on local radial symmetry 1. Although FRS delivers good performance at a relatively low computational cost and is very well suited for a variety of real-time computer vision applications, it is not invariant to perspective distortions. Moreover, even perfectly (radially) symmetric visual patterns in the real world are perceived by us after a perspective projection. In this paper, we propose a systematic extension to the FRS ...

We propose a "shape from texture" method computed on two steps. First a new local scales extraction technique is proposed. The local scale of each point of the picture is computed from an interpolation of wavelet values. Then an interpolation of the local scale map is developed. The method used is an improvement on the one introduced by Lu et

Currently, two-dimensional photographs are most commonly used to facilitate visualization, assessment and treatment of facial abnormalities in craniofacial care but are subject to errors because of perspective, projection, lack metric and 3- dimensional information. One can find in the literature a variety of methods to generate 3-dimensional facial images such as laser scans, stereo-photogrammetry, infrared imaging and even CT however each of these methods contain inherent limitations and as such no systems are in common clinical use. In this paper we will focus on development of indirect 3-dimensional landmark location and measurement of facial soft-tissue with light-based techniques. In this paper we will statistically evaluate and validate a current three-dimensional image-based face modeling technique using a plaster head model. We will also develop computer graphics tools for indirect anthropometric measurements in a three-dimensional head model (or polygonal mesh) including l...

In this study, we present a calibration technique that is valid for all single-viewpoint catadioptric cameras. We are able to represent the projection of 3D points on a catadioptric image linearly with a 6×10 projection matrix, which uses lifted coordinates for image and 3D points. This projection matrix can be computed from 3D–2D correspondences (minimum 20 points distributed in three

We propose a "shape from texture" method computed on two steps. First a new local scales extraction technique is proposed. The local scale of each point of the picture is computed from an interpolation of wavelet values. Then an interpolation of the local scale map is developed. The method used is an improvement on the one introduced by Lu et

We introduce a method for texel extraction on inclined textured planes. This method relies on a technique for determination of local frequencies and the use of a “shape from texture” method derived from the work of Lu et al. (1996). This method allows us to make an adapted extraction to the texture size and the deformations introduced by the perspective

This paper describes an algorithm for the computation of the 3D structure of a road and of the motion state of an in-vehicle CCD camera from the lane borders on the image plane. A parametric model of the projective projection of the lane borders on the image plane is introduced and a fast and reliable algorithm to compute its parameters

Social Language Processing (SLP) is introduced as an interdisciplinary approach to assess social features in communications by terrorist organizations and authoritarian regimes. The SLP paradigm represents a rapprochement of theories, tools and techniques from cognitive science, communications, computational linguistics, discourse processing, language studies and social psychology. The SLP paradigm consists of three broad stages:(1) linguistic feature identification;(2) linguistic feature extraction; and (3) classifier development. In this ...

Food safety represents an increasingly important issue for many governments and using the latest developments from the information and communication technology (ICT) has started to be developed and implemented systems that can provide a better risk management in food industry. A key element in ensuring the food safety is related to food traceability, therefore food traceability systems represent the foundation for every food safety system. Many food and feed business operators have implemented food traceability systems, but maximized capabilities of those systems it is obtained by interconnecting them in order to obtain a functional inter-organizational information system (IOIS). Paper will present an overview regarding main issues related to inter-organizational information system and food safety, after that being discussed an IOIS general architecture for food traceability and presented future research directions. Keywords: Inter-organizational information system, electronic data ...

Certain approaches to the problem of relative orientation in binocular stereo (as well as long-range motion vision) lead to an encoding of the baseline (translation) and orientation (rotation) in a single 3 × 3 matrix called the “essential” matrix. The essential matrix is defined by E = BR, where B is the skew-symmetric matrix that satisfies Bv = b × v for any vector v, with b being the baseline and R the orientation. Shown here is a simple method for recovering the two solutions for the baseline and the orientation from a given essential matrix using elementary matrix operations. The two solutions for the baseline b can be obtained from the equality bbT = 1 2 Trace(EET )I− EET , where I is the 3× 3 identity matrix. The two solutions for the orientation can be found using (b · b)R = Cofactors(E)T − BE, where Cofactors(E) is the matrix of cofactors of E. There is no need to perform a singular value decomposition, to transform coordinates, or to use circular functions, and it is easy ...

It is highly desirable that an imaging system has a single effective viewpoint. Central catadioptric systems are imaging systems that use mirrors to enhance the field of view while keeping a unique center of projection. A general model for central catadioptric image formation has already been established. The present paper exploits this model to study the catadioptric projection of lines. The equations and geometric properties of general catadioptric line imaging are derived. We show that it is possible to determine the position of both the effective viewpoint and the absolute conic in the catadioptric image plane from the images of three lines. It is also proved that it is possible to identify the type of catadioptric system and the position of the line at infinity without further information. A methodology for central catadioptric system calibration is proposed. Reconstruction aspects are discussed. Experimental results are presented. All the results presented are original and completely new.