Ray Tracing and Graphics Standards

Existing standards for three-dimensional graphic representations are unable to produce any realistically shaded images (except PHIGS PLUS, which provides discrete shading only). Ray Tracing or Radiosity are not taken into account up to this time. This article is intended to show one way to integrate the Ray Tracing technique into the pipeline of the graphics standards GKS-3D and PHIGS. No modifications of the viewing concepts are required by our implementation.     

A Library for Developing PHIGS Programming Tools in a PEX Environment

The merger of three-dimensional graphics with the X Window System has recently been standardized by adapting PHIGS, the Programmer's Hierarchical Interactive Graphics System, to the X Window System with PEX, the PHIGS Extension to X. The standard programming library for PEX has been defined to be identical to PHIGS PLUS allowing PHIGS programs to port directly to the X environment. X uses a client server model to run applications as client processes which communicate with a server to perform graphical display and input. For improved performance, the PEX extension defines new server resources to reduce network traffic and to take advantage of graphics hardware existing on high-end servers. A side effect of this distributed model of computation is a distribution of PHIGS structures leading to a relaxation of the exclusive access which a PHIGS application usually maintains over its Central Structure Store. We exploit the distributed nature of a PEX/PHIGS client's Central Structure Store to provide access to it for other applications besides the originating PEX/PHIGS client. We refer to these other applications as tools since one of our primary goals is to create development tools for PHIGS programmers. Rather than concentrate on particular debugging tools, we focus upon easing the process of actually developing tools. Our goal is to supply a collection of routines which can be used by PHIGS programmers to create custom tools or other programs which require access to the graphics data of remote PHIGS processes. Our Tool Development Library provides the PHIGS programmer a small number of management routines which orchestrate the connection and mapping to the data of one or more remote PHIGS applications. Manipulation of remote PHIGS structures is accomplished just as easily as local operations and is performed using standard PHIGS calls. The remote application being accessed requires no changes to its source code. Obvious uses for the Tool Development Library are in the construction of PHIGS tools such as structure browsers, editors and debugging aids. Less obvious is the potential for developing collections of cooperating graphics applications which share graphics data.     

Combining Graphics and Windowing Standards in the XGKS System

In the past few years we have seen the acceptance of standards for both two and three dimensional computer graphics. Also during this time, the workstation community has converged on a common windowing system. This paper discusses the problems encountered in implementing graphics standards such as GKS and PHIGS PLUS within the X Window System environment.     

Parametric Surfaces in PHIGS PLUS: a New Chance for Patterning and Hatching?

The Polygon Fill style PATTERN and HATCH, which are quite successful in 2D graphics standards as GKS¹ and CGI² have proved to be less suitable for 3D graphics standards as GKS-3D³ and PHIGS⁴. However, the emerging standard PHIGS PLUS⁵ offers a unique chance to successfully employ these Interior Styles (under another name and in a slightly different form), because PHIGS PLUS supports a.o. topologically rectangular parametric surfaces In this article it is shown how these Interior Styles could be efficiently applied to curved surfaces in PHIGS PLUS. In addition, the possible interaction between the tessellation method and the patterning is shown.     

DIS中的坐标系统及坐标转换

近几年来,国内正在蓬勃开展对DIS的研究,然而对DIS坐标系统及其转换的研究还不多见。DIS采用地心空间直角坐标系（Geocentric)作为世界坐标系,而现有的大多数仿真器都采用拓扑中心坐标系（Topocentric)或大地坐标系（Geodetic)等坐标系作为世界坐标系。文中旨在介绍DIS标准坐标系及其它几种相关坐标系,并在不同坐标系之间建立了坐标转换关系,同时讨论了不同坐标系中姿态的不同表示方法。算法已应用到我们开发研制的网络接口部件NIU中。     

Homogeneous coordinates

This paper presents an overview of homogeneous coordinates in their relation to computer graphics. A brief historical review is given, followed by the introduction of the homogeneous coordinate system. We elucidate its application in two-dimensional Euclidean space. Particular attention is given to the subjects of affine transformations effected with matrix multiplication and the intersection of two-dimensional lines. Homogeneous coordinates in three dimensions and, in detail, perspective transformations are also discussed. A method for clipping lines with respect to the viewing frustum is provided.     

The Priority Tree, a HL/HSR Approach for PHIGS

The Programmer's Hierarchical Interactive Grahics System (PHIGS) specifies an interface for programming device-independent computer graphics applications. PHIGS provides a powerful data grouping mechanism, called the PHIGS structure, that may be used to model the geometry of 3D objects. Hidden Line/Hidden Surface Removal (HL/HSR) is a required process to produce realistic solid views of the modeled objects. Modeling clip is an essential process for viewing a clipped portion of the modeled objects. A technique is presented that provides HL/HSR and modeling clip as added utilities to PHIGS. The technique is based on the Binary Space Partitioning (BSP) tree (sometimes called priority tree), and involves a back to front sorting of the primitives of a PHIGS structure network to another PHIGS structure. Modeling clip is achieved by limiting the sorting to those primitives in a specified clip ping region of the object space. The resulting structure when displayed on a raster device produces a realistic view of the possibly clipped object that was originally modeled by the PHIGS structure network.     

Triangle Sets in PHIGS PLUS: a Valuable Link with Finite Element Modeling

At the ISO/IEC editing meeting on PHIGS PLUS1 in Villars sur Ollon, Switzerland from 9 to 14 September 1990, an additional output primitive was added to PHIGS PLUS: TRIANGLE SET 3 WITH DATA together with its 2D shorthand. The principal reason for that addition was that only triangular primitives admit uniquely defined interpolation of data (colours, normals, etc.) across the facet.
However, an additional advantage of this new primitive is its value for the visualization of scientific computing results. It corresponds in a very pleasant way with the Finite Element Method using piecewise linear blending functions on a triangular partition of the function domain.
In this paper, an outline will be given of the possible use of this function by Finite Element engineers.
1983 CR Categories: G.1.1, G.1.2,I.3.2,I.3.5,I.3.7, J.6.     

A Method for the Representation, Evaluation and Display of CSG Models in PHIGS and PHIGS+

The Programmer's Hierarchical Interactive Graphics System (PHIGS) is about to become a standard graphics system ^† which caters for the definition, display and modification of two and three-dimensional graphical data.
PHIGS , however, is mainly a wireframe system, and the PHIGS⁺ , extensions to it have been put forward to allow the incorporation of shaded 3D graphics into PHIGS. ,
One area that is important to a large constituency and which has so far not been considered in PHIGS , and PHIGS⁺ , is that of solid modelling. This paper addresses one aspect of solid modelling by describing a simple method for the representation, evaluation and display of Constructive Solid Geometry (CSG) models in PHIGS , and PHIGS⁺. .     

Integrating PHIGS and User Interface Systems

The past five years has seen an explosion of rich and effective user interface management systems and toolkits and an increase in the expectations regarding application portability. Nearly a decade old, the PHIGS input model is inadequate in the face of this variety. "Fixing PHIGS" input would be a long and arduous task. Instead, PHIGS should be adapted to cooperate, not compete, with user interface systems. This can be done in two ways. An application can use both PHIGS input and input from a user interface system to accomplish its goals. Alternatively, an application can use input only from a user interface system, but in this case it needs utilities in PHIGS to gain access to information only PHIGS can supply. Specifically the utilities are needed for application-initiated picking and for coordinate mapping.     

用于导航定位坐标系转换的引申迭代算法研究

为了提升卫星导航信号处理软件RTKLIB的直角坐标转换至大地坐标算法的性能,本文基于牛顿迭代算法的思路,在Bowring直接解法基础上提出一种引申迭代算法。经过理论分析和测试实验数据对比,本文证实了引申迭代坐标转换算法相对于RTILIB现有的一般迭代坐标转换算法,具有迭代次数更少、精度更高的特点,更适用于高度坐标h取值较大的情形。     

城市地下管网增强现实系统研究

针对地下管网管理系统存在的管道图空间沉浸感不强,施工监控和碰撞检测等决策不灵活,地面建筑模型数据存储和渲染的问题,设计了城市地下管网增强现实系统。通过高精度定位服务来加载管道数据,采用七参数坐标转换方法将管道的经纬度坐标转换成Unity3D的数据;利用ARCore实现了管道模型的虚实融合;使用视觉惯性测距（Visual Inertial Odometry,VIO）算法实现对移动设备的跟踪。实验结果表明,该系统可实现管道模型与现实场景相融合,多方位实时查看,实时交互等功能,增强了管网管理的空间决策支持能力,降低了海量地面建筑数据处理的难度。     

A formalization for the specification and systematic generation of computer graphics systems

A formalization of graphical processes in computer graphics systems is presented in terms of functions and their system of axioms. The concept of the viewing pipeline is formalized as operation sequence which is a sequential composition of graphical elementary operations. The formalization includes two kinds of operation sequences which are used as the formal specifications of graphics systems and display devices. In order to generate a graphics system using a display device, we introduced the concept of functionality-preserving transformation of operation sequences in terms of various types of commutations among primitive operations. A type of transformation, which is called extraction, plays a central role in the generation algorithm.     

基于UKF的红外目标空间定位方法

针对单站系统利用一次观测对目标进行定位,瞬时定位误差较大,提出了基于UKF的红外目标空间定位方法。基于针孔成像模型,借鉴主动视觉思想,通过控制红外热像仪运动拍摄目标图像,获取目标位置,并用GPS接收机测得拍摄点世界坐标。根据透视投影变换方程,借助站心地平坐标系和WGS-84坐标系建立红外目标空间定位的非线性系统模型,在此基础上引入UKF（Unscented Kalman Filtering）滤波算法进行空间定位。实验结果证明了该方法的可行性和有效性。     

Visualization of graphical data in a user-specified 2D space using a weighted Isomap method

We present a visualization system for exploring the high-dimensional graphical data, such as textures or 3D models, in 2D space using the dimensionality reduction method. To arrange high-dimensional data in a meaningful 2D space, we develop a novel semi-supervised dimensionality reduction method that can embed data of high dimension in a user-defined 2D coordinate system that is meaningful in terms of the properties of the data. This is achieved by modifying the Isomap method by weighting the data so that the resulting coordinates have no degeneracies and are orthogonal.     

基于坐标变换的图形自适应排列算法

为了解决基于网格技术的图形排列算法在处理可变尺寸图形排列问题上的局限性,基于几何变换思想,建立了有界平面上图形自适应排列的数学模型,并证明了其正确性,进而提出了基于坐标变换的图形自适应排列算法。此算法用图形平移变换方式代替网格划分方法在有界视图上部署图形元素,其时间复杂性为O(N)。最后将所获得的算法应用到面向中央空调节能控制的软PLC系统上,基于9类指令图形、3类测试案例的测试结果表明：本文算法能以较低的CPU占用率实现图形有序排列的效果,具有较高的运行速率与稳定性。     

基于图像匹配的飞行器导航定位算法及仿真

在飞行器导航定位优化控制的研究中,针对无法获得GPS信号时,长航时飞行器捷联惯导系统存在误差,提出了关于图像地标的飞行器精确定位算法,为实现成像系统对捷联惯导系统的误差校正奠定了基础。利用特定地标在机载摄像机像平面上的图像信息,通过图像变换、匹配定位、坐标变换,解算摄像机空间三维坐标和三个姿态角。再根据摄像机坐标系与机体坐标系的变换关系,推算飞行器精确位置。通过计算机仿真对算法进行了验证,结果表明,提出的算法能够满足GPS不可用时长航的飞行器组合导航精度要求,研究结果对长航时飞行器导航具有一定借鉴和参考价值。     

Decomposition of transformation matrices for robot vision

The relationship between the three-dimensional coordinates of a point and the corresponding two-dimensional coordinates of its image, as seen by a camera, can be expressed in terms of a 3 by 4 matrix using the homogeneous coordinate system. This matrix is known more generally as the transformation matrix and it is well known that such a matrix can be determined experimentally by measuring the image coordinates of six or more points in space, whose three-dimensional coordinates are known.Such a transformation matrix can be derived analytically from knowledge of the camera position, orientation, focal length and scaling and translation parameters in the image plane. However, the inverse problem of computing the camera location and orientation from the transformation matrix involves solution of simultaneous nonlinear equations in several variables and is considered difficult.In this paper we present a new and simple analytical technique that accomplishes this inversion rather easily. This technique is quite powerful and has applications to a wide variety of problems in Computer Vision for both static and dynamic scenes. The technique has been implemented as a C program running under Unix and works well on real data.     

GKS Programming in a PHIGS Environment

GKS is an international standard for the functional interface to 2D graphics, whilst PHIGS is currently an ISO work item for 2D and 3D graphics. In addition, PHIGS allows improved control over structuring graphics data in the system. With a new work item, the upwards compatability from GKS to PHIGS is being called into question. This paper is an attempt to give direction to these discussions by listing the implications of introducing a software layer between a GKS application program and a PHIGS environment on which this application is to be run. It is intended to highlight differences between the systems and to answer questions such as, “How compatible?”, “Is it possible?”, “How much does the software layer have to do?”, etc.