Russel A' Apu, Marina L' Gavrilova

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ICCSA 2004 GTVIS Fast and Efficient Rendering
System for Real-Time Terrain Visualization

• Russel A. Apu, Marina L. Gavrilova
• Department of Computer Science
• University of Calgary

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Brief Outline

• Input Processing Methods
• Modified Scheme (improvements)
• Understanding Geo-Morph
• Smoothing Technique
• Texturing
• Experimental Results

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Terminologies

• DEM Digital Elevation Model
• Viewer Dependent Refinement
• ROAM Realtime Optimally Adapting Mesh
• Geo-morph Sequencing
• CLOD Continuous Level of Detail

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Improvements over Original ROAM Scheme

• Preprocessing DEM image
• Smoothing Techniques
• Texturing
• Amortized refinement
• Very efficient
• Higher Frame Rate (45FPS)
• Continuity Geo-morph sequence
• Less variation in frame rate

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Understanding Height FieldsDEM Digital
Elevation Model

• Contains only relative Height
• Regular interval
• Pixel color determine height
• Discrete resolution

X
Kluanne National Park
Y
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Preprocessing of DEM input

• Convolute the surface (2nd Difference)
• Efficient LOD distribution
• Used in Advanced Shading (feature preservation)

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Differentiating the Surface Convolution
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Differentiating the Surface (contd)

• Take Weighted Average of neighboring pixel
  Gradients
• 2 passes gives us the rate of gradient changes

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Statistical Analysis of ROAM

• Bottleneck Split and Merge Operation and
  visibility test
• Only 2.7 Triangles are merged within the visible
  frustum
• 75 of split operations occurs on closest 5
  region of the visible frustum

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Proposed Enhancements

• Reduce overhead for maintaining Split queue
• Degenerated split queue
• Replace priority merge queue (HEAP) with a simple
  FIFO queue.
• Merge arbitrary obscured regions (outside visible
  frustum) only

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Proposed Priority Function for Split Queue

• Determines Refinement
• Distribute LOD to preferred area
• Can be changed
• fface, CCamera
• UUniformity
• FFrustum priority
• DCurvature priority
• PDistance priority
• DETCurvature (preprocessed)
• Lev(f)Subdivision level of face f

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Speeding up the processAmortizing refinement

• Updating the Split queue over multiple frames
• Allow split queue (heap) to degenerate
• Refine integrity using error threshold test
• Re-generate queue after constant number of frames
• Dramatic gain in speed

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Maintaining Degenerated S-Queue
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Understanding Geo-Morph

• Smooth interpolation of vertex over subdivision
• Requires maintenance of one additional queue
  (G-queue)

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Smoothing

• Compute face normal
• Compute vertex normal
• Local computation of normal during refinement
  (Geo-Morph)
• Apply vertex normal when rendering
• Advanced shading Linear combination of face and
  vertex normal (Hybrid)

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Example of smoothing
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Texturing

• Compute uv coordinate during creation of each
  vertex (planar transform)
• Load texture bitmap in the pipeline
• Apply texture handle

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Result with Texturing
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Results (Output obtained)
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Results (Runtime)
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Results (Runtime) (Contd)
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Results (Runtime) (Contd)
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Results (Runtime) (Contd)
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Summary of Result

• High Speed (45 FPS average)
• Continuity is achieved (Geo-Morph)
• Visual appeal (smoothing Texture)
• Less variant Frame rate
• Efficient Understructure (amortized update)

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Finally

• Thank you all.