visualization and graphics research group CIPIC Decimation of Triangle Meshes William J. Schroeder, Jonathan A. Zarge, William E. Lorensen Presented by Alden Chew Serban Porumbescu

visualization and graphics research group CIPIC What is the Problem? Want to visualize data interactively Too many triangles Too little hardware

visualization and graphics research group CIPIC High Level Approach Characterize the local vertex geometry and topology Evaluate decimation criteria for vertex removal Triangulate the resulting hole

visualization and graphics research group CIPIC Vertex Classification Feature edge: dihedral angle greater than user specified feature angle An interior edge vertex is a vertex with two feature edges A corner has one, three, or more feature edges

visualization and graphics research group CIPIC Vertex Removal Based on user specified distance to plane or distance to edge (boundary vertex)

visualization and graphics research group CIPIC Vertex Removal Removal of vertex creates a hole in the mesh –Triangulate Removal of feature edge: –Create a new feature edge –If two non-overlapping loops can be created, triangulate the two loops

visualization and graphics research group CIPIC Triangulate Resulting Hole Triangulate using a recursive loop splitting procedure The stencil of the hole is called a loop Loops are divided into two parts by a split line Split line –A line between two non-adjacent vertices in the loop

visualization and graphics research group CIPIC Split Plane Split plane –The plane orthogonal to the average plane through a split line Used for half space comparisons

visualization and graphics research group CIPIC Loop Splitting Procedure Need to create two non-overlapping loops A valid loop is entirely on one side of the split plane …. If the loop contain more than three vertices, recurse If the loop has three vertices, form a triangle

visualization and graphics research group CIPIC Split Line Selection Many split lines to choose from Choose line that maximizes the aspect ratio The aspect ratio is the minimum distance of the loop vertices to the split plane divided by the length of the split line

visualization and graphics research group CIPIC Special Cases Want to preserve topology Don’t create duplicate triangles and triangle edges

visualization and graphics research group CIPIC Sample Run From VTK (US Patent Number 5,559,388)

visualization and graphics research group CIPIC Skull

visualization and graphics research group CIPIC Blade

visualization and graphics research group CIPIC Hawaii

visualization and graphics research group CIPIC Mars