Chapter 2
Key Concepts

2.1 Intro
2.1.1 Overview
2.1.2 TOC
2.1.3 Conventions

2.2 Overview
2.2.1 File Structure
2.2.2 Header
2.2.3 Scene graph
2.2.4 Prototypes
2.2.5 Routing
2.2.6 Generating files
2.2.7 Presentation
     & Interaction
2.2.8 Profiles

2.3 UTF-8 syntax
2.3.1 Clear text
2.3.2 Statements
2.3.3 Node
2.3.4 Field
2.3.5 PROTO
2.3.6 IS
2.3.7 EXTERNPROTO
2.3.8 USE
2.3.9 ROUTE

2.4 Scene graph
2.4.1 Root nodes
2.4.2 Hierarchy
2.4.3 Descendants
       & ancestors
2.4.4 Hierarchy
2.4.5 Units & coord sys

2.5 VRML & WWW
2.5.1 MIME type
2.5.2 URLs
2.5.3 Relative URLs
2.5.4 data:
2.5.5 Scripting protocols
2.5.6 URNs

2.6 Nodes
2.6.1 Intro
2.6.2 DEF/USE
2.6.3 Geometry
2.6.4 Bboxes
2.6.5 Grouping & children
2.6.6 Lights
2.6.7 Sensors
2.6.8 Interpolators
2.6.9 Time nodes
2.6.10 Bindable children
2.6.11 Textures

2.7 Field, eventIn,
     & eventOut

2.8 PROTO
2.8.1 Declaration
2.8.2 Definition
2.8.3 Scoping

2.9 EXTERNPROTO
2.9.1  Interface
2.9.2  URL
2.9.3 Extensions

2.10 Events
2.10.1 Intro
2.10.2 Routes
2.10.3 Execution
2.10.4 Loops
2.10.5 Fan-in & fan-out

2.11 Time
2.11.1 Intro
2.11.2 Origin
2.11.3 Discrete/cont

2.12 Scripting
2.12.1 Intro
2.12.2 Execution
2.12.3 Initialize/shutdown
2.12.4 eventsProcessed
2.12.5 Direct outputs
2.12.6 Asynchronous
2.12.7 Languages
2.12.8 EventIns
2.12.9 fields & events
2.12.10 Browser interface

2.13 Navigation
2.13.1 Intro
2.13.2 Navigation
2.13.3 Viewing
2.13.4 Collisions

2.14 Lighting
2.14.1 Intro
2.14.2 'off'
2.14.3 'on'
2.14.4 Equations
2.14.5 References

2.13 Navigation

2.13.1 Introduction

Conceptually speaking, every VRML world contains a viewpoint from which the world is currently being viewed. Navigation is the action taken by the user to change the position and/or orientation of this viewpoint thereby changing the user's view. This allows the user to move through a world or examine an object. The NavigationInfo node (see "3.29 NavigationInfo") specifies the characteristics of the desired navigation behaviour, but the exact user interface is browser-dependent. The Viewpoint node (see "3.53 Viewpoint") specifies key locations and orientations in the world that the user may be moved to via scripts or browser-specific user interfaces.

2.13.2 Navigation paradigms

The browser may allow the user to modify the location and orientation of the viewer in the virtual world using a navigation paradigm. Many different navigation paradigms are possible, depending on the nature of the virtual world and the task the user wishes to perform. For instance, a walking paradigm would be appropriate in an architectural walkthrough application, while a flying paradigm might be better in an application exploring interstellar space. Examination is another common use for VRML, where the world is considered to be a single object which the user wishes to view from many angles and distances.

The NavigationInfo node has a type field that specifies the browser the navigation paradigm for this world. The actual user interface provided to accomplish this navigation is browser-dependent. See "3.29 NavigationInfo" for details.

2.13.3 Viewing model

The browser controls the location and orientation of the viewer in the world, based on input from the user (using the browser-provided navigation paradigm) and the motion of the currently bound Viewpoint node (and its coordinate system). The VRML author may place any number of viewpoints in the world at important places from which the user might wish to view the world. Each viewpoint is described by a Viewpoint node. Viewpoints exist in their parent's coordinate system, and both the viewpoint and the coordinate system may be changed to affect the view of the world presented by the browser. Only one viewpoint may be bound at a time. A detailed description of how the Viewpoint node operates may be found in "2.6.10 Bindable children nodes" and "3.53 Viewpoint."

User navigation is independent of the location and orientation of the currently bound Viewpoint node; navigation is performed relative to the Viewpoint's location and does not affect the values of a Viewpoint node. The location of the viewer may be determined with a ProximitySensor node (see "3.38 ProximitySensor").

tip

Viewpoints are a powerful feature for improving usability of your worlds. You can create guided tours by binding the user to a viewpoint and then animating the viewpoint along a predefined path (automatic navigation through the virtual world). Keep in mind that many users will have difficulty navigating through 3D spaces; combining viewports with the other interaction features in VRML creates "point-and-click" worlds that are very easy to navigate.

2.13.4 Collision detection and terrain following

A VRML file may contain Collision nodes (see "3.8 Collision") and NavigationInfo nodes that may influence the browser's navigation paradigm. The browser is responsible for detecting collisions between the viewer and the objects in the virtual world, and is also responsible for adjusting the viewer's location when a collision occurs. Browsers shall not disable collision detection except for the special cases listed below. Collision nodes may be used to generate events when the viewer collides with objects, and may be used to designate that certain objects should be treated as transparent to collisions. Support for inter-object collision is not specified. The NavigationInfo types of WALK, FLY, and NONE shall strictly support collision detection. However, the NavigationInfo types ANY and EXAMINE may temporarily disable collision detection during navigation, but shall not disable collision detection during the normal execution of the world. See "3.29 NavigationInfo" for details on the various navigation types.

NavigationInfo nodes may be used to specify certain parameters often used by browser navigation paradigms. The size and shape of the viewer's avatar determines how close the avatar may be to an object before a collision is considered to take place. These parameters may also be used to implement terrain following by keeping the avatar a certain distance above the ground. They may additionally be used to determine how short an object must be for the viewer to automatically step up onto it instead of colliding with it.