G9: Polygon Meshes Flashcards
What is explicitly defined as a surface in polygon meshes?
A list of polygon vertex coordinates and the connections between vertices to form polygons.
Most commonly, triangle meshes are used.
Why are triangle meshes popular?
They are analogous to raster images in 2D and represent arbitrary surfaces with a set of polygon elements.
They offer a simple data structure composed of flexible base elements, making algorithms simpler and faster.
What is ‘triangle soup’ in the context of encoding triangle meshes?
A method that stores three vertices per triangle, similar to a point cloud, but with triangles implied by each vertex triplet.
It is simple to implement but wasteful as it stores shared vertices multiple times.
What are the advantages of using a ‘vertex list’ and ‘face list’ for encoding triangle meshes?
It defines all vertex coordinates in a list and uses indices to reference these vertices for each triangle, eliminating duplicated vertex coordinates.
However, it remains hard to find triangles sharing vertices and edges.
What is the difference between topology and geometry in the context of meshes?
Topology refers to the global structure and does not care about actual coordinates, while geometry cares about local structure in addition to global structure.
Leveraging topology connections can make mesh operations easier.
What is the half-edge data structure?
A structure that uses a pair of ‘half-edges’ on each side of a shared edge to store information about adjacent faces, vertices, and edges.
It is also known as a ‘doubly connected edge list’ and uses pointers like a linked list.
How do traversal examples using half-edges work?
Traversal is facilitated by next and prev pointers, which make it easy to navigate the mesh and pull out elements using origin, edge, or left pointers.
This structure allows for efficient traversal of the mesh.
How can additional information like colors and surface normals be encoded at vertices?
Attributes for each vertex can be stored in a list, using the same indirection as face list indices.
This is useful for rendering in a rasterization pipeline, such as during shading computations.
Fill in the blank: Topology cares about _______ structure, while geometry cares about _______ structure.
global; local
True or False: The half-edge data structure is more efficient than the ‘triangle soup’ method.
True
