Solid Modelling in computer aided Design
- 2. Evolution of Geometric Modeling • A wireframe representation of an object is done using edges (lines curves) and vertices. • Surface representation is the logical evolution using faces (surfaces), edges and vertices. • In this sequence of developments, the solid modeling uses topological information in addition to the geometrical information to represent the object completely.
- 3. Evolution of Geometric Modeling
- 4. Advantages of Solid Models • Unlike wireframes and surface representations which contain only geometrical data, • The solid model uses topological information in addition to the geometrical information to represent the object completely. • Solid model results in accurate design, helps to further the goal of CAD/ CAM like CIM, Flexible manufacturing leading to better automation of the manufacturing process.
- 5. Advantages of Solid Models • Geometry: The graphical information of dimension, length, angle, area and transformations • Topology: The invisible information about the connectivity, neighbourhood, associatively etc.
- 6. Definition of Solid Model • A solid model of an object is a more complete representation than its surface (wireframe) model. • It provides more topological information in addition to the geometrical information which helps to represent the solid completely.
- 8. Geometric Modeling- Instances • An instance is a scaled / transformed replica of its original. • The scaling may be uniform or differential. • It is a method of keeping primitives in their basic minimum condition like unit cube and unit sphere etc.
- 10. Operation on Primitives • A desired solid can be obtained by combining two or more solids. • When we use Boolean (set) operations the validity of the third (resulting) solid is ensured.
- 12. • Rigidity: Shape of the solid is invariant w.r.t location /orientation. • Homogeneous 3-dimensionality: The solid boundaries must be in contact with the interior. No isolated and dangling edges are permitted. Properties of Solid Models
- 13. • Finiteness and finite describability: Size is finite and a finite amount of information can describe the solid model. • Closure under rigid motion and regularised Boolean operations: Movement and Boolean operations should produce other valid solids. • Boundary determinism: The boundary must contain the solid and hence determine the solid distinctly. Properties of Solid Models
- 14. Classification of Solid Modeling
- 15. 1. Half Spaces. 2. Boundary Representation (B-Rep) 3. Constructive Solid Geometry (CSG) 4. Sweeping 5. Analytical Solid Modeling (ASM) 6. Cell decomposition 7. Spatial Ennumeration 8. Octree encoding 9. Primitive Instancing The 3 most popular schemes: B-rep, CSG, Sweeping Major Modeling Schemes
- 16. Conversion Among Representations • Some representations can be converted to other representations. • CSG to B-REP (but not B-rep to CSG)
- 17. Some Solid Modelers in Practice