Post on 27-Mar-2015
Geometry Clipmaps:Terrain Rendering Using Nested Regular Grids
Geometry Clipmaps:Terrain Rendering Using Nested Regular Grids
Frank LosassoStanford University
Frank LosassoStanford University
Hugues HoppeMicrosoft Research
Hugues HoppeMicrosoft Research
Terrain Rendering ChallengesTerrain Rendering Challenges
• Concise storage No paging hick-ups
• Real-Time frame rates 60 fps
• Visual continuity No temporal pops
• Concise storage No paging hick-ups
• Real-Time frame rates 60 fps
• Visual continuity No temporal pops
Mount Rainier
Olympic Mountains
Primary Dataset:United States at 30m spacing
20 Billion samples
Primary Dataset:United States at 30m spacing
20 Billion samples
Previous WorkPrevious Work
• Irregular Meshes (e.g. [Hoppe 98])
– Fewest polygons– Extremely CPU intensive
• Bin-trees (e.g. [Lindstrom et al 96])
– Simpler data structures / algorithms– Still CPU intensive
• Bin-tree Regions (e.g. [Cignoni et al 03])
– Precomputed regions Decreased CPU cost
– Temporal continuity difficult
• Irregular Meshes (e.g. [Hoppe 98])
– Fewest polygons– Extremely CPU intensive
• Bin-trees (e.g. [Lindstrom et al 96])
– Simpler data structures / algorithms– Still CPU intensive
• Bin-tree Regions (e.g. [Cignoni et al 03])
– Precomputed regions Decreased CPU cost
– Temporal continuity difficult
Previous WorkPrevious Work
• Texture Clipmaps [Tanner 1998]– ‘Infinitely’ large textures– Clipped mipmap hierarchy
• Modeling for the Plausible Emulation of Large Worlds [Dollins 2002]– Quadtree LOD around viewer– Terrain synthesis
• Texture Clipmaps [Tanner 1998]– ‘Infinitely’ large textures– Clipped mipmap hierarchy
• Modeling for the Plausible Emulation of Large Worlds [Dollins 2002]– Quadtree LOD around viewer– Terrain synthesis
Geometry ClipmapsGeometry Clipmaps
• Store data in uniform 2D grids
• Level-of-Detail from nesting of grids
• Refine based on distance
• Main Advantages– Simplicity – Compression– Synthesis
• Store data in uniform 2D grids
• Level-of-Detail from nesting of grids
• Refine based on distance
• Main Advantages– Simplicity – Compression– Synthesis
Terrain as a PyramidTerrain as a Pyramid
Coarsest Level
Finest Level
•Terrain as mipmap pyramid
•LOD using nested grids
•Terrain as mipmap pyramid
•LOD using nested grids
Puget SoundPuget Sound
Individual Clipmap LevelsIndividual Clipmap Levels
• Uniform 2D grid• Indexed triangle strip
– Efficient caching– 60 M triangles/second
• 255-by-255 grid
• Expected Soon:– Vertex Textures
• Uniform 2D grid• Indexed triangle strip
– Efficient caching– 60 M triangles/second
• 255-by-255 grid
• Expected Soon:– Vertex Textures
Inter-Level TransitionsInter-Level Transitions
• Between respective power-of-2 grids• Between respective power-of-2 grids
Inter-Level TransitionsInter-Level Transitions
No transitionNo transition Geometry transitionGeometry transition Geometry & texture transition
Geometry & texture transition
Gaps in geometryGaps in geometry Gaps in texturing/shadingGaps in texturing/shading
Inter-Level TransitionsInter-Level Transitions
• Vertex shader blend geometry
• Pixel shader blend textures– Both are inexpensive
• Vertex shader blend geometry
• Pixel shader blend textures– Both are inexpensive
Clipmap UpdateClipmap Update
• For each level– Calculate new clipmap region– Fill new L-shaped region– Use toroidal arrays for efficiency
• For each level– Calculate new clipmap region– Fill new L-shaped region– Use toroidal arrays for efficiency
Clipmap UpdateClipmap Update
• Update levels coarse-to-fine– Use limited update budget– Only render updated data
Fine levels may be cropped
Rendering load decreases as update load becomes to large for the budget
• Update levels coarse-to-fine– Use limited update budget– Only render updated data
Fine levels may be cropped
Rendering load decreases as update load becomes to large for the budget
‘Filling’ New Regions‘Filling’ New Regions
• Two Sources:– Computed on-demand at 60 frames/second
• Two Sources:– Computed on-demand at 60 frames/second
Decompressed explicit terrain
Decompressed explicit terrain
Synthesized new terrain
Synthesized new terrain
Clipmap UpdateClipmap Update
• Fine level from coarse level
• U is a 16 point C1 smooth interpolant
• For synthesized terrain, X = Gaussian noise• For explicit terrain, X = compression residual
• Fine level from coarse level
• U is a 16 point C1 smooth interpolant
• For synthesized terrain, X = Gaussian noise• For explicit terrain, X = compression residual
Terrain SynthesisTerrain Synthesis
• Adds high frequency detail
• Upsample then add Gaussian noise
– Precomputed 50-by-50 noise texture– Per-octave amplitude from real terrain
• Adds high frequency detail
• Upsample then add Gaussian noise
– Precomputed 50-by-50 noise texture– Per-octave amplitude from real terrain
Texture SynthesisTexture Synthesis
Subdivision InterpolantSubdivision Interpolant
Bilinear Interpolant (C0)Bilinear Interpolant (C0) 16-point Interpolant (C1)16-point Interpolant (C1)
Terrain CompressionTerrain Compression
• Create mipmap fine-to-coarse
• D found from data such that:
• Create mipmap fine-to-coarse
• D found from data such that:
Terrain CompressionTerrain Compression
• Calculate residuals coarse-to-fine– Upsample and compute
inter-level residual
– Quantize and compress residual
– Replace approximation Prevent error accumulation
• Calculate residuals coarse-to-fine– Upsample and compute
inter-level residual
– Quantize and compress residual
– Replace approximation Prevent error accumulation
Compression ResultsCompression Results
• U.S height map– 30m horizontal spacing– 1m vertical resolution– 216,000-by-93,600 grid– 40GB uncompressed
– 350MB compressed factor of over 100– rms error 1.8m (6% of sample spacing)
• U.S height map– 30m horizontal spacing– 1m vertical resolution– 216,000-by-93,600 grid– 40GB uncompressed
– 350MB compressed factor of over 100– rms error 1.8m (6% of sample spacing)
Compression ResultsCompression Results
LOD schemeNumber of samples
Runtime space
Bytes per sample
Hoppe [98] 8 M 50 MB 6.0
Lindstrom [02] 256 M 5.0 GB 19.5
Cignoni et al [02] 64 M 115 MB 1.8
Geometry Clipmaps 20 G 375 MB 0.02
Level-of-detail ErrorLevel-of-detail Error
• Analyzed statistically See paper
• For U.S. terrain (640-by-480 resolution)– rms error = 0.15 pixels– max error = 12 pixels– 99.9th percentile = 0.90 pixels
• Analyzed statistically See paper
• For U.S. terrain (640-by-480 resolution)– rms error = 0.15 pixels– max error = 12 pixels– 99.9th percentile = 0.90 pixels
United States of AmericaUnited States of America
Graphics Hardware FriendlyGraphics Hardware Friendly
• Can be implemented in hardware– Clipmap levels as high-precision textures– Subdivision and normal calculation [Losasso et al 03]
– Morphing already done in hardware– Noise from Noise() or from texture
• Uploaded on-demand– Decompressed terrain
• Can be implemented in hardware– Clipmap levels as high-precision textures– Subdivision and normal calculation [Losasso et al 03]
– Morphing already done in hardware– Noise from Noise() or from texture
• Uploaded on-demand– Decompressed terrain
LimitationsLimitations
• Statistical error analysis– Assumes bounded spectral density
• Unnecessarily many triangles– Assumes uniformly detailed terrain
but, allows for optimal rendering throughput
• Statistical error analysis– Assumes bounded spectral density
• Unnecessarily many triangles– Assumes uniformly detailed terrain
but, allows for optimal rendering throughput
AdvantagesAdvantages
• Simplicity
• Optimal rendering throughput
• Visual continuity
• Steady rendering
• Graceful degradation
• Compression
• Synthesis
• Simplicity
• Optimal rendering throughput
• Visual continuity
• Steady rendering
• Graceful degradation
• Compression
• Synthesis