ANSI INCITS ISO IEC 14772-1-1997 Information technology - Computer graphics and image processing - The Virtual Reality Modeling Language - Part 1 Functional specification and UTF-8.pdf

1、INTERNATIONAL ISOAEC STANDARD 14772-l First edition 1997-12-15 Information technology - Computer graphics and image processing - The Virtual Reality Modeling Language - Part 1: Functional specification and UTF-8 encoding Technologies de /information - lnfographie et traitement de /image - Le langage

2、 de mod6lisation de r6alit6 virtue/e - Partie 1: Spbcification fonctionnelle et codage UTF-8 Reference number ISO/IEC 14772-1:1997(E) Adopted by INCITS (InterNational Committee for Information Technology Standards) as an American National Standard.Date of ANSI Approval: 3/31/99Published by American

3、National Standards Institute,25 West 43rd Street, New York, New York 10036Copyright 2002 by Information Technology Industry Council (ITI).All rights reserved.These materials are subject to copyright claims of International Standardization Organization (ISO), InternationalElectrotechnical Commission

4、(IEC), American National Standards Institute (ANSI), and Information Technology Industry Council(ITI). Not for resale. No part of this publication may be reproduced in any form, including an electronic retrieval system, withoutthe prior written permission of ITI. All requests pertaining to this stan

5、dard should be submitted to ITI, 1250 Eye Street NW,Washington, DC 20005.Printed in the United States of AmericaISOAEC 14772-l :1997(E) Foreword *Foreword IS0 (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form a specialized system for wo

6、rldwide standardization. National bodies that are members of IS0 or IEC participate in the development of International Standards through technical committees established by the respective organization to deal with particular fields of technical activity. IS0 and IEC technical committees collaborate

7、 in fields of mutual interest. Other international organizations, governmental and non-governmental, in liaison with IS0 and IEC, also take part in the work. See http:/www.iso.ch for information on IS0 and http:/www.i ec . ch for information on IEC. In the field of information technology, IS0 and IE

8、C have established a joint technical committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as an International Standard requires approval by at least 75% of the national bodies casting a vote. See ht

9、tp:/www.iso.ch/meme/JTCl.html forinformationonJTC1. International Standard ISO/IEC 14772 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology, Subcommittee 24, Computer graphics and image processing, in collaboration with The VRML Consortium, Inc. (http: /www. vrml. orc$ a

10、nd the VRML moderated email list (www- vrmlvrml.org). ISO/IEC 14772 consists of the following part, under the general title Information technology - Computer graphics and image processing - The Virtual Reality Modeling Language: Part I: Functional spec$cation and UTF-8 encoding. Further parts will f

11、ollow. Annexes A to C form an integral part of this part of ISO/IEC 14772. Annexes D to F are for information only. This part of ISOiIEC 14472 is distributed as both a hard copy edition and an HTML tile which is on the attached CD-ROM. The paper and the electronic versions contain the same material.

12、 However, the structure and presentation are more relevant to the document as viewed on-screen. Please note that the electronic file must be viewed using a recent version of a web browser. 0 ISOllEC 1997 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced o

13、r utilized in any form or by any means, electronic or mechanical, including photocopying and micro- film, without permission in writing from the publisher. ISO/IEC Copyright Office . Case postale 56 l CH-1211 Genkve 20 l Switzerland Printed in Switzerland ii 0 ISO/IEC Introduction ISO/IEC 14772-1:19

14、97(E) *Purpose The Virtual Reality Modeling Language (VRML) is a file format for describing interactive 3D objects and worlds. VRML is designed to be used on the Internet, intranets, and local client systems. VRML is also intended to be a universal interchange format for integrated 3D graphics and m

15、ultimedia. VRML may be used in a variety of application areas such as engineering and scientific visualization, multimedia presentations, entertainment and educational titles, web pages, and shared virtual worlds. *Design Criteria VRML has been designed to fulfill the following requirements: Authora

16、bility Enable the development of computer programs capable of creating, editing, and maintaining VRML files, as well as automatic translation programs for converting other commonly used 3D file formats into VRML files. Composability Provide the ability to use and combine dynamic 3D objects within a

17、VRML world and thus allow re-usability. Extensibility Provide the ability to add new object types not explicitly defined in VRML. Be capable of implementation Capable of implementation on a wide range of systems. Performance Emphasize scalable, interactive performance on a wide variety of computing

18、platforms. Scalability Enable arbitrarily large dynamic 3D worlds. *Characteristics of VRML VRML is capable of representing static and animated dynamic 3D and multimedia objects with hyperlinks to other media such as text, sounds, movies, and images. VRML browsers, as well as authoring tools for the

19、 creation of VRML files, are widely available for many different platforms. VRML supports an extensibility mode1 that allows new dynamic 30 objects to be defined . . . 111 ISO/IEC 14772-1:1997(E) 0 ISO/IEC allowing application communities to develop interoperable extensions to the base standard. The

20、re are mappings between VRML objects and commonly used 3D application programmer interface (API) features. INTERNATIONAL STANDARD 0 ISO/IEC ISO/IEC 14772-1:1997(E) Information technology - Computer graphics and image processing - The Virtual Reality Modeling Language - Part 1: Functional specificati

21、on and UTF-8 encoding 1 Scope ISO/IEC 14772, the Virtual Reality Modeling Language (VRML), defines a file format that integrates 3D graphics and multimedia. Conceptually, each VRML file is a 3D time-based space that contains graphic and aural objects that can be dynamically modified through a variet

22、y of mechanisms. This part of ISO/IEC 14772 defines a primary set of objects and mechanisms that encourage composition. encapsulation, and extension. The semantics of VRML describe an abstract functional behaviour of time-based, interactive 3D, multimedia information. ISO/IEC 14772 does not define p

23、hysical devices or any other implementation-dependent concepts (e.g., screen resolution and input devices). ISO/IEC 14772 is intended for a wide variety of devices and applications, and provides wide latitude in interpretation and implementation of the functionality. For example, ISO/IEC 14772 does

24、not assume the existence of a mouse or 2D display device. Each VRML file: a. implicitly establishes a world coordinate space for all objects defined in the file, as well as all objects included by the file: b. explicitly defines and composes a set of 3D and multimedia objects; C. can specify hyperli

25、nks to other files and applications; d. can define object behaviours. An important characteristic of VRML files is the ability to compose files together through inclusion and to relate files together through hyperlinking. For example, consider the file earth. wrl which specifies a world that contain

26、s a sphere representing the earth. This file may also contain references to a variety of other VRML files representing cities on the earth (e.g., tile paris. wrl). The enclosing file, earth. wrl, defines the coordinate system that all the cities reside in. Each city file defines the world coordinate

27、 system that the city resides in but that becomes a local coordinate system when contained by the earth file. Hierarchical file inclusion enables the creation of arbitrarily large, dynamic worlds. Therefore, VRML ensures that each file is completely described by the objects contained within it. Anot

28、her essential characteristic of VRML is that it is intended to be used in a distributed environment such as the World Wide Web. There are various objects and mechanisms built into the language that support multiple 1 ISO/IEC 14772-1:1997(E) 0 ISODEC distributed files, including: e. in-lining of othe

29、r VRML files; f. hyperlinking to other files; t.2. using established Internet and IS0 standards for other file formats; h. defining a compact syntax. VRrmsT - Q 0 ISOiIEC ISOAEC 14772-1:1997(E) 2 Normative references lIRlTl - Q The following normative documents contain provisions which, through refe

30、rence in this text, constitute provisions of this part of ISO/IEC 14772. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this part of ISO/IEC 14772 are encouraged to investigate the possibility of applyi

31、ng the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of IS0 and IEC maintain registers of currently valid International Standards. Annex E, Bibliowaohy, contains a list of informative

32、 documents and technology. 1 1 L ( I E E I I I I I dentifier I Reference 766 I :GM 7 IETF RFC 1766, Tags for the Identification of Languages, Internet standards track protocol. http:/ 1766.txt ISO/IEC 8632: 1992 (all parts) Information technology - Computer graphics - Metafile for the storage and tr

33、ansfer of picture description information. http:/www.iso.ch/isob/switch-engine-cate.pl?searchtvpe=refnumber see ZllJTF81. The usage of UTF-8 is detailed in 6.47, Text, node. The header for a UTF-8 encoded VRML tile is #VFWL V2.0 utf8 optional comment Any characters after the on the first line may be

34、 ignored by a browser. The header line ends at the occurrence of a . A is a linefeed character(OxOa) or a carriage-return character (OxOd) 4.2.3 Scene graph The scene graph contains nodes which describe objects and their properties. It contains hierarchically grouped geometry to provide an audio-vis

35、ual representation of objects, as well as nodes that participate in the event generation and routing mechanism. 4.2.4 Prototypes Prototypes allow the set of VRML node types to be extended by the user. Prototype definitions can be included in the tile in which they are used or defined externally. Pro

36、totypes may be defmed in terms of other VRML nodes or may be defined using a browser-specific extension mechanism. While ISO/IEC 14772 has a standard format for identifying such extensions, their implementation is browser-dependent. 4.2.5 Event routing Some VRML nodes generate events in response to

37、environmental changes or user interaction. Event routing gives authors a mechanism, separate from the scene graph hierarchy, through which these events can be propagated to effect changes in other nodes. Once generated, events are sent to their routed destinations in time order and processed by the

38、receiving node. This processing can change the state of the node, generate additional events, or change the structure of the scene graph. Script nodes allow arbitrary, author-defined event processing. An event received by a Script node causes the execution of a function within a script which has the

39、 ability to send events through the normal event routing mechanism, or bypass this mechanism and send events directly to any node to which the Script node has a reference. Scripts can also dynamically add or delete routes and thereby changing the event-routing topology. The ideal event model process

40、es all events instantaneously in the order that they are generated. A timestamp serves two purposes. First, it is a conceptual device used to describe the chronological flow of the event mechanism. It ensures that deterministic results can be achieved by real-world implementations that address proce

41、ssing delays and asynchronous interaction with external devices. Second, timestamps are also made available to Script nodes to allow events to be processed based on the order of user actions or the elapsed time between events. 21 ISO/IEC 14772-1:1997(E) 0 ISO/IEC 4.2.6 Generating VRML files A genera

42、tor is a human or computerized creator of VRML files. It is the responsibility of the generator to ensure the correctness of the VRML file and the availability of supporting assets (e.g., images, audio clips, other VRML files) referenced therein. 4.2.7 Presentation and interaction The interpretation

43、, execution, and presentation of VRML files will typically be undertaken by a mechanism known as a browser, which displays the shapes and sounds in the scene graph. This presentation is known as a virtual world and is navigated in the browser by a human or mechanical entity, known as a user. The wor

44、ld is displayed as if experienced from a particular location: that position and orientation in the world is known as the viewer. The browser provides navigation paradigms (such as walking or flying) that enable the user to move the viewer through the virtual world. In addition to navigation, the bro

45、wser provides a mechanism allowing the user to interact with the world through sensor nodes in the scene graph hierarchy. Sensors respond to user interaction with geometric objects in the world, the movement of the user through the world, or the passage of time. The visual presentation of geometric

46、objects in a VRML world follows a conceptual model designed to resemble the physical characteristics of light. The VRML lighting model describes how appearance properties and lights in the world are combined to produce displayed colours (see 4.14, Lighting Model, for details). Figure 4.1 illustrates

47、 a conceptual model of a VRML browser. The browser is portrayed as a presentation application that accepts user input in the forms of file selection (explicit and implicit) and user interface gestures (e.g., manipulation and navigation using an input device). The three main components of the browser

48、 are: Parser, Scene Graph, and Audio/Visual Presentation. The Parser component reads the VRML file and creates the Scene Graph. The Scene Graph component consists of the Transformation Hierarchy (the nodes) and the Route Graph. The Scene Graph also includes the Execution Engine that processes events

49、, reads and edits the Route Graph, and makes changes to the Transform Hierarchy (nodes). User input generally affects sensors and navigation, and thus is wired to the Route Graph component (sensors) and the Audio/Visual Presentation component (navigation). The Audio/Visual Presentation component performs the graphics and audio rendering of the Transform Hierarchy that feeds back to the user. 4.2.8 Profiles ISO/IEC 14772 supports the concept of profiles. A profile is a named collection of functionality and requirements which shall be supported i