CHAI 3D

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CHAI 3D

• EECE 511, Introduction to Virtual Reality
• PPT based on Siggraph 2005 presentation of CHAI3D

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CHAI 3D

• An Open-Source Toolkit for Haptic Rendering
  Applications
• A useful platform used by many research labs
  working on haptics for various purposes

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FEATURES OF CHAI3D

• Open source
• C Open GL based
• Supports most commercially available desktop
  devices.
• Supports for I/O boards
• Supports for various compilers on various OSs
• Supports for integration of ODE
• Can be used as a
• Low level API to talk to devices
• High level API with visual and haptic rendering
  supports

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SUPPORTING HW

• Force dimension Products (Omega,Delta)
• Sensable Products (Phantom, Omni)
• MPB Freedom 6S
• Virtual device

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COMPARISONS OF OPEN HAPTICS

• CHAI 3D
• Open source, transparent structure
• You can modify almost everything
• Support typical scenegraph built-in force
  rendering algorithm
• The best library for haptic oriented project
• Open Haptics (HDLibrary)
• Device API
• You must make everything except device
  communication and scheduler.
• Open Haptics (HLLibrary)
• You cannot modify anything
• You can add haptics to your existing OpenGL
  program without many modification

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PRELIMINARY HAPTIC RENDERING PIPELINE
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PRELIMINARY COLLISION DETECTION

• To determine whether the interaction tool is in
  contact with any virtual object in the database.
• Main ideas common to the collision detection
  algorithms
• Smart data structure (e.g., those using bounding
  boxes and spatial partitioning)
• Smart transition between global and local search

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PRELIMINARY AXIS ALIGNED BOUNDING BOX (AABB)
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PRELIMINARY VECTOR FIELD METHOD

• Vector field
• Determines response forces directly from
  penetrations of the HIP.
• 11 mapping of an interior point to the response
  force

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PRELIMINARY VIRTUAL PROXY ALGORITHM

• Virtual proxy is an ideal interaction sphere.
• It stays on the surface when the object
  penetration occurs.
• It locates on the nearest surface from the HIP.

Virtual proxy
HIP
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PRELIMINARY RESPONSE FORCE COMPUTATION
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STRUCTURE OF CHAI 3D
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OVERALL STRUCTURE OF CHAI3D
Object-wiseCollision Detection Algorithm (AABB)
Camera
World
Light
Object (Mesh ForceField)

Object (Mesh ForceField)
Tool(Device)
Tool(Device)
CollisionDetection Algorithm

Object (Mesh ForceField)
Object (Mesh ForceField)
Rendering Algorithm
CollisionDetection Algorithm
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CLASSES GRAPHICS

• Supports multiple scene-graphs
• A scene contains
• A world
• Lights
• Cameras
• Meshes

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CLASSES GRAPHICS

• Objects are inherited from the cGenericObject
  class
• Transform properties
• Bounding box
• Objects have various graphical features
• Graphic textures
• Vertex colors
• Transparency
• Object also have haptic features
• Stiffness
• Friction properties

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GRAPHICS SCENE GRAPH
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CLASSES DEVICES TOOLS
Tool

• Device classes
• Low-level interfaces to haptic devices
• Start-stop
• Read position/forces
• Command force/pose
• Tools classes
• High-level interfaces to haptically enabled
  virtual tools
• They are part of the scenegraph
• They call collision detection and force rendering
  algorithms to compute forces
• They communicate to devices associated with them

Rendering Algorithm
Device
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CLASSES DEVICES TOOLS

• The cPhantomDevicesclass allows you to directly
  talk a Phantom device
• useful if you already have your own virtual
  environment setup and just need to talk to a
  device
• The cPhantom3dofPointer allows you to have a
  three degrees of freedom pointer to poke objects
  present in the chai3d scenegraph
• useful if you are using chai3d to manage virtual
  environment and force rendering algorithms

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EXAMPLE OF USING TOOLS

• Can add a 3dof tool to our scenegraph to touch
  the mesh in the system
• All collision detection an force rendering calls
  are handled transparently

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THE VIRTUAL DEVICE

• Some drawbacks of most haptic devices
• expensive
• not easy to carry around
• very hard to debug
• easy to break
• It allows to
• move a pointer in 3D with a mouse
• visualize forces returned from the chai3d
  application

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CLASSES FORCES AND COLLISION DETECTION, FILES

• Force rendering algorithms supported (only 3dof)
• God-object , virtual proxy algorithm with
  friction (Zilles 95 , Salisbury 97)
• Potential fields
• Collision detection algorithms supported
• line to mesh using AABB trees
• line to mesh using Spheres hierarchies
• File types supported for meshes
• OBJ Alias Wavefront file format
• 3Ds 3d Studio Max file format

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CLASSES TIMERS

• Haptic rendering of stiff surfaces becomes
  unstable for low servo rates
• Typical rates are 1KHz
• This can be hard under Windows and thus
• most haptic devices have some way to emulate Real
  Time behavior
• chai3d approach use Windows Multimedia Timers,
  accurate up to 1KHz

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A TYPICAL CHAI3D APPLICATION

• Initialization
• Instantiate world, camera, light, objects, tool
• Add everything to world
• Instantiate viewport and timer
• Haptic callback (1kHz)
• Read tool position, compute force, apply tem
• Visual callback (30Hz)
• Render viewport

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A TYPICAL CHAI3D APPLICATION

• Initialization

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A TYPICAL CHAI3D APPLICATION

• Visual callback
• Haptic callback

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LEARNING CHAI3D

• download chai3d from
• http//www.chai3d.org
• build libraries using your favorite compiler
• add the chai3d/bin folder to your path
• look at the examples
• look at Doxygen documentation