Practical Data Visualization and Virtual Reality. Virtual Reality Practical VR Implementation. Karljohan Lundin Palmerius

Transcription

1 Practical Data Visualization and Virtual Reality Virtual Reality Practical VR Implementation Karljohan Lundin Palmerius

2 Scene Graph Directed Acyclic Graph (DAG) Hierarchy of nodes (tree) Reflects hierarchy of objects Traversed for processing Structure Data structure / data exchange formats Standards (VRML, X3D, MPEG-4, etc) Software Unity3D H3D API OpenSceneGraph (OSG)

3 Scene Graph Program package (Partly) replaces graphics API Should not hinder...only help Framework Extend with new functionality Application Scene Graph OpenGL Hardware Display

4 VRML/X3D Style Transforms are groups Implicit separation Shape nodes Selected properties Geometry child No leaking property

5 Node Reuse More than one parent Share child node Less memory use Less code Less to update

6 VRML/X3D Molecule Example Water Molecule 1 Oxygen 2 Hydrogen

7 X3D Code Tree structure Node children are specified as node contents Hierarchy reflected in XML structure XML nodes become scene graph nodes E g <Group><Group/></Group> Default field name for all nodes Explicitly define container e g containerfield= xyz Values are specified as attributes E g <Material diffusecolor= />

8 H3D API Multi-modal scene graph Implementing and extending X3D X3D scene graph definition Python engines C++ node implementation and extension Extended further by Candy my own utilities toolkit HVR my own Virtual Reality toolkit VHTK my own multi-modal volume visualization toolkit

9 H3D API Documentation H3DAPI.org Doxygen automatically generated html pages Manually written help in Wiki Contains also Candy and VHTK documentation

10 How to Make Use of Documentation Documentation of Procedurial API: Flat structure Typically separate data and function listing Documentation of Object Oriented API: (e.g. doxygen) Hierarchical object structures Base class tells us something about how the class is used Methods and their documentation may be in a base class Class members Public/protected attributes Public/protected functions (methods) H3D fields listed under Public Attributes Experience is needed!

11 H3D API Hierarchies

12 H3D API Attributes

13 X3D Code <Group> <Transform rotation=" " scale=" "> <Transform DEF="OXYGEN" translation="0 0 0"> <Shape> <Appearance><Material diffusecolor=" "/></Appearance> <Sphere radius="0.2"/> </Shape> </Transform> <Transform DEF="HYDROGEN_1" translation=" "> <Shape DEF="H_SHAPE"> <Appearance><Material diffusecolor=" "/></Appearance> <Sphere radius="0.1"/> </Shape> </Transform> <Transform DEF="HYDROGEN_2" translation=" "> <Shape USE="H_SHAPE"/> </Transform> </Transform> </Group>

14 Networked Objects Event Systems

15 Event Systems Networked Objects (Design Pattern) Define data flow Automated run-time processing Software H3D API Visualization Toolkit (VTK) Voreen (Volume Rendering Engine) Inviwo Qt etc...

16 H3D API Networked scene graph Events in the scene graph More tasks given to scenegraph Program distributed as engines Connecting fields Sending values Event network

17 Event Systems Nodes Fields Define properties of nodes Contain data: colour, translation, light intensity, etc Hold other nodes: children, appearance, geometry, etc Sensors Encapsulate a behaviour Event sources: Timers, triggers, mouse, etc Engines Activated by incoming events Process incoming data and computes new data

18 Event Systems Fields Contains values, e g SField, MField Contains nodes, e g SFNode, MFNode Copy values, calculate new values Copy pointers, create new objects Require good reference counters Routing One field value to many fields Engine may accept many input Lazy evaluation

19 Simple Example 3D mouse sensor Controls object transform SFVec3f rawtranslation SFVec3f accumulatedtranslation SFRotation rawrotation SFRotation accumulatedrotation SFInt32 buttons Connect field route from 3D mouse translation field route to X-form translation field

20 VR Software Systems

21 VR Software for Display Systems Application Scene Graph VR Software OpenGL Hardware Display

22 VR Software Systems Purpose set up cluster nodes and start the VR software handle per display settings, such as viewpoints handle state serialization and synchronization perform necessary undistortion and filtering connect to tracking systems, audio, etc.