Graphics Interface 2009 The-Kiet Lu Kok-Lim Low Jianmin Zheng 1

 Rendering high-detail surface (>100M points) is inefficient when vertices are independently processed one-by-one in real-time Redundant processing  Occlusion  LOD  # of pixels vs. # of vertices  1024x1024 pixels vs. 368 millions points  Memory size  1 vertex requires > 6 bytes (un-compressed)  St. Mathew (368 M) > 2Gbs  Simplification – slow Requires surface reconstruction first 2

 Hybrid approach Object-space and screen-space solution Display 3D models by per-pixel ray-casting a set of 2D height fields (displacement mapping) 3

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 1) 2D Height Field Construction Decompose points using octree Generate height field maps Generate height field bounding boxes  2) Height Field Rendering Rasterize bounding box. For each fragment rasterized:  Transform viewing ray to height field map coordinate space  Ray-casting — compute ray-surface intersection. 5

 Decompose points using an octree so that each cell contains points forming a valid height field 6

 Using PCA to determine Height Field domain plane. Height Field map is generated as displaced distance between the Surface and the PCA plane. 7

 The faces of the octree cells that bounds the height filed surface are added into Vertex buffer with appropriately assigned texture coordinates. 8

 Each fragment, the viewing ray is transformed from world coordinate frame into locals of the corresponding 2D height map. 9

 We compute intersection by marching along the viewing ray from initial location to the closet point above the Height Field map.  Culling Test:  A simple Texture coordinate check to ensure the ray indeed intersects the current height map – not the neigh borings. X i = X i-1 + v x ∆h v 10

 Hybrid approach Optimize  Automatic Screen-space occlusion culling  Back Face culling  Early Z-culling  Memory consumption  6 bytes vertex vs. 8-bit depth buffer  Texture compression Limitation  Performance subjects to screen resolution 11

12 A main advantage of our method is its simplicity in dealing with silhouettes correctly.

13 1 iterations 4 iterations 8 iterations

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60 368M  Comparison: point-based Mar2007 : 60M per second – our method results with 368M (St. Mathew) with 12 Fps on GeForce Go 7900 GPU - Intel Core 2 Duo 2.4 GHz.. 18

 We have presented a new approach for fast visualization of highly detail 3D models by decomposition 3D model into Height Fields and render these Height Fields using image-space ray- casting algorithm that offers significant performance improvement compared to previous point-based approach.  Our current limitation is that it is not efficient for flat and smooth surfaces as well as not applicable for dynamic or deformable surfaces – our current research topic. 19