Mesh data structure & file format GI127 陳勁宇. Content Object File Format(OFF) Polygon File...
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Transcript of Mesh data structure & file format GI127 陳勁宇. Content Object File Format(OFF) Polygon File...
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Object File Format(OFF)Polygon File Format(PLY)The Winged-Edge Data StructureThe Half-Edge Data Structure
Object File Format(OFF)
Storing a description a 2D or 3D objectSimple extension can handle 4D objects 4D: (x,y,z,w)
OFF File Characteristics ASCII (there is also a binary version) Color optional 3D No compression
Polygon File Format
Stanford Triangle FormatStore 3-d data from 3D scannersProperties can be stored including color and transparency surface normals texture coordinates data confidence values
Stanford 3D Scanning Repository (url)
Cyberware 3D Scanners (url)
Large models also avaiable at GeogiaTech
The Winged-Edge Data Structure
Commonly used to describe polygon modelsQuick traversal between faces, edges, verticesLinked structure of the network
Assume there is no holes in each face
The Winged-Edge Data Structure
vertices of this edgeits left and right facesthe predecessor and successor when traversing its left facethe predecessor and successor when traversing its right face.
The Winged-Edge Data Structure
Edge Vertices Faces Left Traverse Right Traverse
Name Start End Left Right Pred Succ Pred Succ
a X Y 1 2 d b c e
Edge Table
The Winged-Edge Data Structure
Edge Vertices Faces Left Traverse Right
Traverse
Name Start End Left Right Pred Succ Pred Succ
a A D 3 1 f e c b
b A B 1 4 a c d f
c B D 1 2 b a e d
d B C 2 4 c e f b
e C D 2 3 d c a f
f A C 4 3 b d e a
The Winged-Edge Data Structure
Vertex Name Incident Edge
A a
B b
C d
D c
the vertex table and the face tablemultiple choices of edges
Face Name Incident Edge
1 a
2 c
3 a
4 b
The Winged-Edge Data Structure
For a face with inner loops are ordered clockwise.
Adding an auxiliary edge between each inner loop and the outer loop
Euler-Poincare Formula (url)
V: the number of vertices E: the number of edges F: the number of faces G: the number of holes that penetrate the solid, usually referred to as genus in topology S: the number of shells. A shell is an internal void of a solid. A shell is bounded by a 2-manifold surface, which can have its own genus value. Note that the solid itself is counted as a shell. Therefore, the value for S is at least 1.L: the number of loops, all outer and inner loops of faces are counted.
Then, the Euler-Poincaré formula is the following:
V - E + F - (L - F) - 2(S - G) = 0