VTK: The Visualization Toolkit

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VTK The Visualization Toolkit

• Part II Visualization Model
• March 30, 2001

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VTK Visualization Models

• Graphics and Visualization Model
• Graphics objects rendering
• Visualization objects generating geometry

Data Flow System Pipeline execution
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What is visualization anyway?

• Converting data from its original form into
  graphics
• Deal with the issues of transformation and
  representation
• Transformation data to graphics
• Representation internal data structures
• Example stock price display ?

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Representations

• Computational representation An array of stock
  prices.
• Pricei 9085, 9080, 9075, 9060, 9068, .
• Timei 10(am), 1030, 11, 1130, 12,
• Graphical Representation x-y plot

Computational Graphics
Transformation (visualization)
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A 3D example

• Visualization process
• Sample the function f(x,y,z) -gt a 3D array on
• a regular grid Fxyz f (-1
  lt x,y,z lt 1)
• Generate a 3D surface corresponding to f(x,y,z)
  c
• Display the surface Sample the function

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Visualization Process
f(x,y,z)
sample
Transformation (visualization)
Computational representation
Graphical representation
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Object-oriented viewpoint
VTK Visualization Model

• Representation Object model
• internal data structures
• Transformation Functional model
• the steps to create visualization (how data flow
  through the system)

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VTK Functional Model
Illustrate the steps to create visualization,
also called Visualization Pipeline (visualizatio
n networks)
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VTK Object Model

• Describe which objects operate on the functional
• model (visualization pipeline)
• Data Object Represent information and methods
  to
• create, access, and delete the
  information
• example the 3D point array
  F(x,y,z)
• Process Object operates on (transform) the data
  objects
• example generating surfaces
  from F(x,y,z)

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Process Objects

• Source Interface to external data sources
• or generate data procedurally
• Filter Transform the data input
• Mapper The sink of the functional model,
• interface with the graphics model

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Process Objects (contd)
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Data Objects

• Data Object dataset
• (representation of information)
• Structures how the information is organized
• - Topology
• - Geometry
• Attributes store the information we want
• to visualize. e.g.
  function values

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Data Objects structures

• Topology
• Invariant under geometric transformation
• (rotation, translation, scaling etc)
• - Topological structures Cells
• Geometry
• The instantiation of the topology
• Geometric structures cells with
• positions in 3D space

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VTK Cell Types
(d) polyline
(e) triangle
(b) Polyvertex
(c) line
(a) vertex
(e) Quadrilateral
(e) Polygon
(f) Tetrahedron
(f) Hexahedron
And more (I am too tired drawing now )
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VTK Data Attributes

• The information stored at each corner of the cell
• Scalars temperature, pressure, etc
• Vector velocitys
• Normals surface directions
• Texture coordinates graphics specific
• Tensors matrices

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Where are we now ...
Remember

• Data Object dataset
• (representation of information)
• Structures how the information is organized
• - Topology
• - Geometry
• Attributes store the information we want
• to visualize. e.g.
  function values

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VTK Datasets
A Collection of structures and attributes
Structured Grid
Rectilinear Grid
Unstructured Points
Polygonal Grid
Unstructured Grid
Structured Grid
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Examples
vol.cxx
Ugrid.cxx
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Pipeline Execution
Direction of update
Render
Visualization model Graphics model
Source Filter Mapper
Actor
Direction of data flow