20010528j d cunha1 object-oriented visualization joão duarte cunha univ. de lisboa - faculdade de...

1J D Cunha20010528

Object-oriented VisualizationObject-oriented Visualization

João Duarte CunhaJoão Duarte Cunha

Univ. de Lisboa - Faculdade de CiênciasUniv. de Lisboa - Faculdade de Ciências

Socrates ProgrammeSocrates Programme

Plzen, May 2001Plzen, May 2001

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VisualizationVisualization

Overcoming spatial, temporal and Overcoming spatial, temporal and physical barriersphysical barriers

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Sensorial limitationsSensorial limitations

• Our senses are our “interface”: everything Our senses are our “interface”: everything we got from the outside world comes we got from the outside world comes through themthrough them

• Our senses are quite limitedOur senses are quite limited– in the type of stimuli they can perceivein the type of stimuli they can perceive– in their sensitivityin their sensitivity

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Sensorial limitationsSensorial limitations

• Because of those limitations, the world Because of those limitations, the world within our reach is:within our reach is:– limited in spacelimited in space– limited in timelimited in time– limited in the type of objects and phenomena limited in the type of objects and phenomena

that we can perceive!that we can perceive!

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Man’s inconformismMan’s inconformism

• Man always struggled against his sensorial Man always struggled against his sensorial limitations!limitations!

• Oral tradition in primitive societies was a Oral tradition in primitive societies was a away of overcoming the time barrier (and, away of overcoming the time barrier (and, combined with travelling, also the space combined with travelling, also the space barrier)barrier)

• Painting and other art forms have a similar Painting and other art forms have a similar role!role!

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• The introduction of writing was an The introduction of writing was an enormous step forward.enormous step forward.

• And the discovery of the press by And the discovery of the press by Gutemberg in the 15th century amplified its Gutemberg in the 15th century amplified its impact by orders of magnitude.impact by orders of magnitude.

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• And so we got the 19th century!And so we got the 19th century!

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• All these ways of overcoming the space and All these ways of overcoming the space and time barriers are human mediatedtime barriers are human mediated– by ONE man in the case of writing and the by ONE man in the case of writing and the

plastic artsplastic arts– by MANY men in the case of oral tradition, by MANY men in the case of oral tradition,

music, dance.music, dance.

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• The senses involved are always vision and The senses involved are always vision and hearing!hearing!

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• Galileo’s telescope and other optical Galileo’s telescope and other optical instruments pushed away the space barrier.instruments pushed away the space barrier.

And we know well howAnd we know well how

important this was forimportant this was for

our understanding of our understanding of

the universe!the universe!

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• With the development of measuring With the development of measuring instruments the struggle against the physical instruments the struggle against the physical barrier proceeded step by step.barrier proceeded step by step.

• But slowly!But slowly!

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• In the 19th century a new era begun!In the 19th century a new era begun!– Telegraphy (1856) introduced the “instanta-Telegraphy (1856) introduced the “instanta-

neous” transmission of the written word.neous” transmission of the written word.

We can say, at Earth scale at least,We can say, at Earth scale at least,

that with telegraphythat with telegraphy

space became independent of time!space became independent of time!

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• The telephone (1876) and radio or wireless The telephone (1876) and radio or wireless telephony (already in the 20th century) are telephony (already in the 20th century) are new advances allowing for a limited form new advances allowing for a limited form of direct (not human mediated) perception.of direct (not human mediated) perception.

• Photography (1839), sound recording Photography (1839), sound recording (1877) and the cinema (1895) are other (1877) and the cinema (1895) are other important landmarks.important landmarks.

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• But it was undoubtedly the television But it was undoubtedly the television (1926) the most significant step in man’s (1926) the most significant step in man’s struggle against the space barrier!struggle against the space barrier!

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"Sensing" information "Sensing" information

• From Visualization to "Perception" !From Visualization to "Perception" !

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SEEING informationSEEING information• Knowledge is based on information and action Knowledge is based on information and action

is determined by knowledge.is determined by knowledge.

• Computers are essential to generate new Computers are essential to generate new information (simulation and data acquisition).information (simulation and data acquisition).

• But they are, more than anything else, the But they are, more than anything else, the ideal instrument to store, search, retrieve and ideal instrument to store, search, retrieve and process information.process information.

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SEEING informationSEEING information

• In their book "Readings in Information In their book "Readings in Information Visualization - Using vision to think", Visualization - Using vision to think", Card, Mackinlay e Shneiderman define Card, Mackinlay e Shneiderman define visualization asvisualization as

The use of computer-supported,The use of computer-supported,

interactive, visual representationsinteractive, visual representations

of data to amplify cognitionof data to amplify cognition

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Look at the following table:

0,000 0,087 0,174 0,259 0,342 0,423 0,500 0,574

0,643 0,707 0,766 0,819 0,866 0,906 0,940 0,966

0,985 0,996 1,000 0,996 0,985 0,966 0,940 0,906

0,866 0,819 0,766 0,707 0,643 0,574 0,500 0,4230,342 0,259 0,174 0,087 0,000

and at the graph in the following slide:and at the graph in the following slide:

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0,000

0,200

0,400

0,600

0,800

1,000

1,200

0 50 100 150 200

Series1

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• These two slides just point out what we These two slides just point out what we already knew very well: our ability to get already knew very well: our ability to get information is highly dependent on its form.information is highly dependent on its form.– In general, a graph or image allow a much In general, a graph or image allow a much

faster understanding than a list of numbers or a faster understanding than a list of numbers or a textual description.textual description.

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• Visualization was used long before, but the Visualization was used long before, but the Scientific Visualization and Information Scientific Visualization and Information Visualization areas were born in the late Visualization areas were born in the late 80’s.80’s.

• The confluence of “push” and “pull” factors The confluence of “push” and “pull” factors was determinant for that.was determinant for that.

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• ““Push” factorsPush” factors– 30 years of experience in Computer Graphics30 years of experience in Computer Graphics

– Availability of powerful graphical hardwareAvailability of powerful graphical hardware

– Developments in human-machine interfacesDevelopments in human-machine interfaces

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• ““Pull” factorsPull” factors– Ever greater amounts of data to store and Ever greater amounts of data to store and

analyze coming from:analyze coming from:

• Sophisticated simulations made possible by the Sophisticated simulations made possible by the available computing poweravailable computing power

• Very large and complex data basesVery large and complex data bases

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• Simplified reference model for visualizationSimplified reference model for visualization

DataData MappingMapping RenderingRendering

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Mapping

Information is converted into Information is converted into geometry and/or graphical attributes.geometry and/or graphical attributes.

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Scientific VisualizationScientific Visualization

• Scientific Visualization or Visualization of Scientific Visualization or Visualization of Scientific Data is usually defined as concer-Scientific Data is usually defined as concer-ned with visualization of data associated ned with visualization of data associated with a spatial grid, as opposed to Informa-with a spatial grid, as opposed to Informa-tion Visualization which concentrates on tion Visualization which concentrates on more abstract kinds of data.more abstract kinds of data.

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The Visualization Toolkit - vtkThe Visualization Toolkit - vtk

• VTKVTK is an object-oriented toolkit for 3D is an object-oriented toolkit for 3D graphics(http://www.kitware.com/vtk.html)graphics(http://www.kitware.com/vtk.html)

• Although tailored for the scientific visuali-Although tailored for the scientific visuali-zation field it can also be sucessfully used zation field it can also be sucessfully used to illustrate the basics of 3D graphics and to illustrate the basics of 3D graphics and rendering.rendering.

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• The toolkit consists of a set of C++ classes The toolkit consists of a set of C++ classes providing the functionality to build 3D providing the functionality to build 3D graphics applications, namely visualization graphics applications, namely visualization applications, without the need for any low applications, without the need for any low level programming.level programming.

• Vtk is compatible with several graphical Vtk is compatible with several graphical systems, namely OpenGL and X-Windows.systems, namely OpenGL and X-Windows.

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• Vtk may be used from C++, Java or Tcl/Tk Vtk may be used from C++, Java or Tcl/Tk programmes.programmes.

• In this talk Tcl/Tk will be used.In this talk Tcl/Tk will be used.

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• Vtk being object-oriented, we need only to Vtk being object-oriented, we need only to create objects of the appropriate types and create objects of the appropriate types and call the available methods.call the available methods.

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• Vtk object types can be grouped according Vtk object types can be grouped according to their functionality.to their functionality.

• The most important object groups are: The most important object groups are: Sources, Mappers, Graphics and Filters.Sources, Mappers, Graphics and Filters.

• We will now look in some detail at each We will now look in some detail at each group.group.

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• SourcesSources are information provider objects.are information provider objects.

• Some sources are readers, that is, they get Some sources are readers, that is, they get the information from files in appropriate the information from files in appropriate formats. Examples:formats. Examples:– vtkPLOT3DReadervtkPLOT3DReader– vtkBYUReadervtkBYUReader– vtkPolyDataReader (one of vtk own formats)vtkPolyDataReader (one of vtk own formats)

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• Others generate data algorithmically. The Others generate data algorithmically. The typical example are the sources that create typical example are the sources that create basic geometric shapes likebasic geometric shapes like– vtkSphereSourcevtkSphereSource– vtkCylinderSourcevtkCylinderSource– vtkConeSourcevtkConeSource

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• MappersMappers, as suggested by the name itself, , as suggested by the name itself, get the information provided by source get the information provided by source objects, directly or through appropriate objects, directly or through appropriate filters, and generate graphic primitives.filters, and generate graphic primitives.

• There are two types of mappers:There are two types of mappers:– vtkDataSetMappervtkDataSetMapper– vtkPolyDataMappervtkPolyDataMapper

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• A special type of mappers are the writers, A special type of mappers are the writers, which write out information in files with which write out information in files with differente formats. Examples:differente formats. Examples:– vtkBYUWritervtkBYUWriter– vtkTIFFWritervtkTIFFWriter– vtkPolyDataWritervtkPolyDataWriter

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• Objects in the Objects in the graphicsgraphics group are respon- group are respon-sible for the rendering portion of the visua-sible for the rendering portion of the visua-lization pipeline.lization pipeline.

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• Objects in this group include:Objects in this group include:– vtkRenderervtkRenderer– vtkRenderWindowvtkRenderWindow– vtkActorvtkActor– vtkPropertyvtkProperty– vtkTransformvtkTransform– vtkCameravtkCamera– vtkLightvtkLight

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• vtkRenderer is a virtual class.vtkRenderer is a virtual class.

• But vtkOpenGLRenderer, which inherits But vtkOpenGLRenderer, which inherits from vtkRenderer, is a concrete class from vtkRenderer, is a concrete class instan-tiated when the graphics systems is instan-tiated when the graphics systems is OpenGL.OpenGL.

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• Objects of type vtkRenderWindow repre-Objects of type vtkRenderWindow repre-sent the application window.sent the application window.

• The window will be a Windows window or The window will be a Windows window or an X window, according to the graphics an X window, according to the graphics system being used.system being used.

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• Each instance of vtkActor represents a Each instance of vtkActor represents a scene “object”, combining the geometry scene “object”, combining the geometry (provided by the mapper) with the optical (provided by the mapper) with the optical properties (colour, texture, etc) and con-properties (colour, texture, etc) and con-crete values for the location, orientation and crete values for the location, orientation and size.size.

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• Instances of vtkProperty are associated with Instances of vtkProperty are associated with actors to control its appearance.actors to control its appearance.

• Similarly, instances of vtkTransform are Similarly, instances of vtkTransform are associated with actors to determine their associated with actors to determine their location, orientation and size.location, orientation and size.

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• Instances of vtkCamera and vtkLight are Instances of vtkCamera and vtkLight are associated with Renderer objects to specify associated with Renderer objects to specify how the scene is seen and illuminated.how the scene is seen and illuminated.

• If the user does not explicitely create If the user does not explicitely create objects of these two types, default ones are objects of these two types, default ones are provided.provided.

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• FiltersFilters are “transformation” objects and are “transformation” objects and there are many types of filters available.there are many types of filters available.

• For example, the marching cubes and mar-For example, the marching cubes and mar-ching squares algorithms are implemented ching squares algorithms are implemented as filters. The same is true for decimation, as filters. The same is true for decimation, sampling, geometry extraction, threshol-sampling, geometry extraction, threshol-ding, particle and many other algorithms.ding, particle and many other algorithms.

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The visualization pipeline in vtkThe visualization pipeline in vtk

• The simplest pipeline includes a source, a The simplest pipeline includes a source, a mapper and an actor.mapper and an actor.

• To be seen, actors must be associated with a To be seen, actors must be associated with a renderer and the renderer associated to a renderer and the renderer associated to a window.window.

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The visualization pipeline in vtkThe visualization pipeline in vtk

Cubo_S Cubo_M Cubo_A

rw r

vtkProperty

vtkTransform

vtkCamera

vtkLight

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Case studyCase study

• We will now see and briefly discuss the We will now see and briefly discuss the application of vtk to meteorological data.application of vtk to meteorological data.

• The data was provided by the Lisbon The data was provided by the Lisbon Meteorological Institute (IM) for use in a Meteorological Institute (IM) for use in a course of Computer Graphics for physics course of Computer Graphics for physics students.students.

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• The data were collected with intervals of six The data were collected with intervals of six hours between April 5 at 12h and April 6 at hours between April 5 at 12h and April 6 at 12h.12h.

• Physical quantities measured are Tempera-Physical quantities measured are Tempera-ture, Humidity, Altitude and Wind velocity ture, Humidity, Altitude and Wind velocity along the parallel and along the meridian. along the parallel and along the meridian.

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• The grid is topologically and geometrically The grid is topologically and geometrically regular (cartesian grid), covering a region regular (cartesian grid), covering a region from -45º W to 45º E and from 80º N to 20º from -45º W to 45º E and from 80º N to 20º N, at 0.5º intervals.N, at 0.5º intervals.

• This means a total of 108000 data points for This means a total of 108000 data points for each physical quantity.each physical quantity.

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• The data were measured at the so called The data were measured at the so called “mid-atmosphere”, defined as the 500 hPa “mid-atmosphere”, defined as the 500 hPa isobaric.isobaric.

• We will start by having a look at the data We will start by having a look at the data using WebWinds, a visualization program using WebWinds, a visualization program developped by the Jet Propulsion Lab developped by the Jet Propulsion Lab (http://www.jpl.nasa.gov/directory)(http://www.jpl.nasa.gov/directory)

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• WebWinds is also object-oriented, but the WebWinds is also object-oriented, but the objects are provided with a complete inter-objects are provided with a complete inter-face and a visual programming approach face and a visual programming approach was adopted.was adopted.

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• Now the vtk application.Now the vtk application.

• First the essential parts of the Tcl code.First the essential parts of the Tcl code.

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• # Create RenderWindow and Renderer# Create RenderWindow and Renderer• vtkRenderer ren1vtkRenderer ren1• vtkRenderWindow renWinvtkRenderWindow renWin• renWin AddRenderer ren1renWin AddRenderer ren1

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• # Get the Temperature data# Get the Temperature data• vtkStructuredPointsReader readervtkStructuredPointsReader reader• reader SetFileName reader SetFileName "dados_meteo_T_vtk.vtk""dados_meteo_T_vtk.vtk"

• reader Updatereader Update

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• # Extract planes for each time slice# Extract planes for each time slice• # Plane 0# Plane 0• vtkStructuredPointsGeometryFilter vtkStructuredPointsGeometryFilter compPlanecompPlane

• compPlane SetInput [reader GetOutput]compPlane SetInput [reader GetOutput]• compPlane SetExtent 0 200 0 200 0 0compPlane SetExtent 0 200 0 200 0 0• vtkPolyDataMapper planeMappervtkPolyDataMapper planeMapper• planeMapper SetInput [compPlane planeMapper SetInput [compPlane GetOutput]GetOutput]

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• planeMapper ScalarVisibilityOnplaneMapper ScalarVisibilityOn• eval planeMapper SetScalarRange eval planeMapper SetScalarRange [[[[reader GetOutput] GetPointData] [[[[reader GetOutput] GetPointData] GetScalars] GetRange]GetScalars] GetRange]

• vtkActor planeActorvtkActor planeActor• planeActor SetMapper planeMapperplaneActor SetMapper planeMapper• planeMapper SetColorModeToLuminanceplaneMapper SetColorModeToLuminance• [planeActor GetProperty] [planeActor GetProperty] SetRepresentationToSurfaceSetRepresentationToSurface

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• # Plane 1# Plane 1• ..........• # Plane 2# Plane 2• ..........• # Plane 3# Plane 3• ..........• # Plane 4# Plane 4• ..........

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• # Cut data using a plane# Cut data using a plane• vtkPlane planevtkPlane plane• # Plane contains the volume center# Plane contains the volume center• eval plane SetOrigin [[reader eval plane SetOrigin [[reader GetOutput] GetCenter]GetOutput] GetCenter]

• # and is parallel to the latitude and # and is parallel to the latitude and time axistime axis

• plane SetNormal 1 0 0plane SetNormal 1 0 0• vtkCutter planeCutvtkCutter planeCut

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• planeCut SetInput [reader GetOutput]planeCut SetInput [reader GetOutput]• planeCut SetCutFunction planeplaneCut SetCutFunction plane• vtkDataSetMapper cutMappervtkDataSetMapper cutMapper• cutMapper SetInput [planeCut GetOutput]cutMapper SetInput [planeCut GetOutput]• cutMapper SetColorModeToLuminancecutMapper SetColorModeToLuminance• eval cutMapper SetScalarRange [[[[reader eval cutMapper SetScalarRange [[[[reader GetOutput] GetPointData] GetScalars] GetOutput] GetPointData] GetScalars] GetRange]GetRange]

• vtkActor cutActorvtkActor cutActor• cutActor SetMapper cutMappercutActor SetMapper cutMapper

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• # Draw the outline# Draw the outline• vtkOutlineFilter outlinevtkOutlineFilter outline• outline SetInput [reader GetOutput]outline SetInput [reader GetOutput]• vtkPolyDataMapper outlineMappervtkPolyDataMapper outlineMapper• outlineMapper SetInput [outline outlineMapper SetInput [outline GetOutput]GetOutput]

• vtkActor outlineActorvtkActor outlineActor• outlineActor SetMapper outlineMapperoutlineActor SetMapper outlineMapper• eval [outlineActor GetProperty] SetColor eval [outlineActor GetProperty] SetColor 0 0 00 0 0

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• # Add actors to the renderer# Add actors to the renderer• ren1 AddActor outlineActorren1 AddActor outlineActor• ren1 AddActor planeActorren1 AddActor planeActor• ren1 AddActor planeActor1ren1 AddActor planeActor1• ren1 AddActor planeActor2ren1 AddActor planeActor2• ren1 AddActor planeActor3ren1 AddActor planeActor3• ren1 AddActor planeActor4ren1 AddActor planeActor4• ren1 AddActor cutActorren1 AddActor cutActor

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• # Adjust camera# Adjust camera• set cam1 [ren1 GetActiveCamera]set cam1 [ren1 GetActiveCamera]• $cam1 SetClippingRange 3.95297 50$cam1 SetClippingRange 3.95297 50• $cam1 SetFocalPoint 0 50 3$cam1 SetFocalPoint 0 50 3• $cam1 SetPosition 0 28 -200$cam1 SetPosition 0 28 -200• $cam1 ComputeViewPlaneNormal$cam1 ComputeViewPlaneNormal• $cam1 SetViewUp 0 -0.99 0.06$cam1 SetViewUp 0 -0.99 0.06

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• #Get the rendering done!#Get the rendering done!

• renWin RenderrenWin Render

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• Now we are ready to play with the Now we are ready to play with the application itselfapplication itself

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Case StudyCase Study

Thank you for your attention!Thank you for your attention!

20010528j d cunha1 object-oriented visualization joão duarte cunha univ. de lisboa - faculdade de...

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