Smooth View-Dependent Level-of-Detail Control and its Application to

Terrain Rendering

Hugues Hoppe

Microsoft Research

Introduction To address the problem:

view-dependent LOD control View-dependent progressive mesh(VDPM) In this paper,

Extend the VDPM framework to provide temporal coherence through the runtime creation of geomorph

Introduction Implementation

Which require new output-sensitive data structures.

Added benefitReducing memory used.

Contribution of this paperA real-time flyover of a large ,rugged terrain.

Introduction This paper is the first runtime scheme for v

iew-dependent LOD control on arbitrary meshes.

PS: View-Dependent Refinement of Progressive Meshes(VDPM)

Hugues Hoppe(siggraph 1997)

Review of VDPM Framework

Review of VDPM Framework1. The root nodes correspond to the vertices of the ba

se mesh Mo2. The leaf nodes correspond to the fully detailed me

sh Mn

Review of VDPM Framework Fully Refined mesh (Mn) Selectively Refined mesh (Ms) We say that a vertex or face is active if it exists

in the selectively refined mesh Ms.

Review of VDPM Framework Geomorph

Review of VDPM Framework A vsplit refinement is performed if its nei

ghborhood satisfies 3 criteria

1. It intersects the view frustum

2. Its Gauss map is not strictly oriented away

3. Its screen-projected deviation from Mn exceeds a user-specified pixel tolerance.

Efficient,Temporally Smooth VDPM

Efficient,Temporally Smooth VDPM Output-sensitive data structures Runtime generation of geomorphs

Efficient,Temporally Smooth VDPM Output-sensitive data structures

All its data structures scale proportionally with the size n of the fully refined mesh Mn

1. Static part: Encoding the vertex hierachy and refinement dependency

2. Dynamic part: Encoding the connectivity of just the active mesh M

Efficient,Temporally Smooth VDPM Runtime generation of geomorphs

Two factors are crucial to a good visual flythrough simulation:

1. A (high) steady frame rate

2. The absence of popping artifacts

Efficient,Temporally Smooth VDPM Popping occurs in an animation when

successive frames show different approximate models that are visually discontinuous.

Efficient,Temporally Smooth VDPM Two goals (frame rate,popping) seem contradi

ctory. To maintain a constant frame rate

Adjusting the screen-space error tolerance. To eliminate popping

Smoothly morphing the geometry.

Efficient,Temporally Smooth VDPM

Specialization of VDPM to Terrains

Specialization of VDPM to Terrains Exact approximation error

We measure the maximum approximation error with respect to a reference surface.

We therefore want to compute the maximum height deviation between this trangulated grid and the open neighborhood of each edge collapse transformation.

The maximum height deviation between two triangle meshes is known to lie at a vertex of their union partition in the plane.

Specialization of VDPM to Terrains An efficient way to enumerate the vertices

of the union partition is to consider:

1. The grid points internal to the faces adjacent to Vs

2. The grid line crossings internal to the edges adjacent to Vs

Specialization of VDPM to Terrains

Result

Result

Result

報告完畢