Solid Modelling

Solid modeling:
Solid modeling (or modelling) is the unambiguous representation of the solid parts of an object, that is, models of solid objects suitable for computer processing. It is also known as volume modeling. Other modeling methods include surface models (used extensively in automotive and consumer product design as well as entertainment animation) and wire frame models (which can be ambiguous about solid volume).Primary uses of solid modeling are for CAD, engineering analysis, computer graphics and animation, rapid prototyping, medical testing, product visualization and visualization of scientific research

Basic theoretical concepts:
It has been suggested that Parametric feature based modeler be merged into this article or section. (Discuss) It has been suggested that Change state be merged into this article or section. (Discuss) It has been suggested that Transmigration operation be merged into this article or section. (Discuss) It has been suggested that Euler boolean operation be merged into this article or section. (Discuss) There are several ways by which a solid model may be constructed, usually from simpler objects (such as surfaces, lines, and/or points).
Sweeping:
An area feature is "swept out" by moving a primitive along a path to form a solid feature. These volumes either add to the object ("extrusion") or remove material ("cutter path"). Also known as 'sketch based modeling'. Analogous to various manufacturing techniques such as extrusion, milling, lathe and others.
Boundary representation (BRep) :
A solid object is represented by boundary surfaces and then filled to make solid. Also knowing as 'surfacing'. Analogous to various manufacturing techniques; Injection moulding, casting, forging, thermoforming, etc. Parameterized primitive instancing: An object is specified by reference to a library of parameterized primitives. For example, a bolt is modeled for a library, this model is used for all bolt sizes by modifying a set of its parameters.
Spatial occupancy enumeration (voxel) :
The whole space is subdivided into regular cells, and the object is specified by the set of cells it occupies. Models described this way lend themselves to Finite difference analysis. This is usually done after a model is made, as part of automated pre-processing for analysis software.
Cellular decomposition :Similar to "spatial occupancy", but the cells are neither regular, nor "prefabricated". Models described this way lend themselves to FEA. This is usually done after a model is made, as part of automated pre-processing for analysis software.
Constructive solid geometry (CSG) :
Simple objects (primitives) are combined using Boolean operations (union, difference, intersection) and linear transformations. A special data structure is called a CSG-tree, where primitives are leaves and operations are nodes. Function representation (FRep) :Any object is represented by a single real function of point coordinates. A point is outside the object if the function is negative, inside the object if the function is positive, and on the boundary if the function is zero (isosurface). The function is evaluated at a point by traversing a tree structure similar to the CSG-tree.
Feature based modeling :
Complex combinations of objects and operators are considered together as a unit which can be modified or duplicated. Order of operations is kept in a history tree, and parametric changes can propagate through the tree.
Parametric modeling :
Attributes of features are parameterized, giving them labels rather than only giving them fixed numeric dimensions, and relationships between parameters in the entire model are tracked, to make changing numeric values of parameters easier. Almost always combined with features, giving parametric feature based modeling.
Facet modeling :
Forming the outside surface form of the volume from any triangular planes Often used in reverse engineering of physical models

History:
Solid modeling has to be seen in context of the whole history of CAD, the key milestones being the development of Romulus which went on to influence the development of Parasolid and ACIS and thus the mid-range Windows based feature modelers such as IronCAD, Alibre Design, SolidWorks, and Solid Edge and the arrival of parametric solid models system like T-Flex and Pro/ENGINEER