CAE: Engineering Visualization

1
CAE Engineering Visualization

• CAE visualization shares common definitions (and
  challenges) with Computer Graphics
• Making pictures with computers includes many
  areas including modeling, transformations,
  shading, pixel and volume display, display
  architecture, software and hardware algorithms

2
CAE Engineering Visualization

• Graphics process involves modeling with a
  modeling database, geometry transformations with
  viewing parameters, display with frame buffer and
  video display
• Of particular interest would be visualization of
  large volumes of data Example stress and
  displacement results (of an analysis) on an
  assembly of parts, with animation.

3
CAE Visualization benefits

• Decreased physical testing
• Greater Integration of Design and Analysis
• Increased analysis Complexity and Sophistication
• Design Optimization
• Productivity and Accuracy

4
CAE Visualization Modeling

• Modeling objects can be done using points and
  lines in wireframe modeling. Same as graphical
  polygon mesh representation
• More complex graphical repesentations use
  splines, Bsplines, patches, etc.,
• Implicit definition such as x2y2z21 is quite
  useful for volumes as models

5
CAE Volumetric Visualization

• Implicit surface model to data can be used to
  model internal structures Example bone structure
  modeled as volumetric data using density
  variations
• Focus on properties of objects to model. In case
  of animation of volumes, material and mass will
  have to be considered, for others mass is not
  required.

6
CAE Graphical Transformations

• Modeling transformations canonical object and
  its instances
• Instance transformations positioning of the
  instances (in world coordinate system), created
  with modeling transforms
• Viewing transformations camera coordinate system
  for viewing and display

7
CAE Transformation example

• Sphere can be transformed into an ellipsoid with
  modeling transform with x5, y3. An instance
  transform could be applied to rotate 20 degrees
  about Z and translate center to (20,10,-5).
  Viewing transform will transform it for viewing
  from (100,200,50) looking at a point (0,10,10).
• Lighting models and viewports are needed

8
CAE Engineering Visualization

• Scaling, Rotation and shearing can be used for
  affine graphical transformations
• Translation could be accomplished using a
  homogeneous coordinate system such as (x, y,w) in
  2D and (x,y,z,w) in 3D
• Perspective projections will provide a non-affine
  transformation. Foreshortening effect

9
CAE Engineering Display

• A window is the view from a camera
• Window is usually mapped to a section of the
  screen called Viewport. Rectangular area with
  sides parallel to screen coordinate axis
• Clipping decides what is visible in a viewport.
  Lines do not clip the same as polygons (figure
  2.10)

10
CAE Engineering Display

• Display primitives and modeling primitives will
  be different. Scan conversion (also called
  rasterization) deals with painting the pixels
  with the right color.
• Convex polygons scan-convert easier than
  non-convex polygons (figure 2.11a, 2.11b)
• A single segment is defined by intersecting a
  scan line with the polygon

11
CAE Graphical Coloring

• Coloring pixels based on lighting and properties
  of the entities (surfaces)
• Illumination models, shading models are common
• Lighting is either directional (parallel rays
  with intensity and direction are only parameters)
  or point (3d position and intensity)

12
CAE Graphical Lighting

• Intensity is power per unit area for directional
  light sources and power per solid angle for point
  light source
• Color is handled with RGB model (red, green,
  blue) in many systems
• Illumination has modes of reflected light
  ambient, diffuse, specular

13
CAE Lighting Models

• Ambient is constant light. For visibility.
• Diffuse emulates reflection typical of matte
  objects. Diffuse is independent of direction of
  view.
• Specular simulates behavior of glossy materials.
  Direction sensitive (maximum in the direction of
  pure mirror reflection - falls off as angle
  increases)

14
CAE Shading Models

• Gouraud Shading Color is interpolated for all
  interior from computed values at vertices
• Phong Shading Normals are interpolated from
  computed values at vertices
• These models help to hide the transitions and
  discontinuities along the edges of the polygons

15
CAE Texture Mapping

• Map from a pixel to a surface of the object to
  the image, where the image plays a role of the
  texture of the surface
• Images can be scanned in from real object images
• Surface normal, transparency, reflectivity could
  be texture mapped

16
CAE Visibility / Hidden Line

• Hidden Line or Hidden Surface removal is needed
  to show what is visible in a view
• Painters algorithm with binary space
  partitioning trees - good for simple cases
• Z-buffer / Depth-buffer hardware implementable.
  Each pixel computed for smallest Z-value of
  objects covering it after perspective
  transformation.

17
CAE Ray Tracing

• Intersects a primitive with a ray for pixel based
  rendering. Easy to implement effects such as
  shadows, reflections, refractions
• Intersections could be expensive, lots of checks
  with each object in the scene.
• 50000 primitives, 5minutes on a 50Mips workstation

18
CAE Display Architecture

• Volume visualization. Object primitives are
  volume elements or voxels
• Display architecture includes model processor,
  transform processor, scan converter, frame
  buffer, video control with color map, CRT/display
  (figure 2.17, 2.18)
• Multimedia and HDTV developments