Editing Solid modeling (section)

== Computer-aided design ==
{{Main|Computer-aided design}}
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The modeling of solids is only the minimum requirement of a [[Computer-aided design#Capabilities|CAD system's capabilities]]. Solid modelers have become commonplace in engineering departments in the last ten years{{When|date=December 2011}} due to faster computers and competitive software pricing. Solid modeling software creates a virtual 3D representation of components for machine design and analysis.<ref name="LaCourse Handbook">{{cite book|last=LaCourse|first=Donald|title=Handbook of Solid Modeling|publisher=McGraw Hill|year=1995|pages=2.5|chapter=2|isbn=978-0-07-035788-4}}</ref> A typical [[graphical user interface]] includes programmable macros, keyboard shortcuts and dynamic model manipulation. The ability to dynamically re-orient the model, in real-time shaded 3-D, is emphasized and helps the designer maintain a mental 3-D image.

A solid part model generally consists of a group of features, added one at a time, until the model is complete. Engineering solid models are built mostly with sketcher-based features; 2-D sketches that are swept along a path to become 3-D. These may be cuts, or extrusions for example. Design work on components is usually done within the context of the whole product using [[assembly modelling|assembly modeling]] methods. An assembly model incorporates references to individual part models that comprise the product.<ref name="LaCourse Handbook 11.3">{{cite book|last=LaCourse|first=Donald|title=Handbook of Solid Modeling|publisher=McGraw Hill|year=1995|pages=111.2|chapter=11|isbn=978-0-07-035788-4}}</ref>

Another type of modeling technique is 'surfacing' ([[Freeform surface modeling]]). Here, surfaces are defined, trimmed and merged, and filled to make solid.  The surfaces are usually defined with datum curves in space and a variety of complex commands. Surfacing is more difficult, but better applicable to some manufacturing techniques, like injection molding. Solid models for injection molded parts usually have both surfacing and sketcher based features.

[[Engineering drawing]]s can be created semi-automatically and reference the solid models.

===Parametric modeling===
Parametric modeling uses parameters to define a model (dimensions, for example). Examples of parameters are: dimensions used to create model features, material density, formulas to describe swept features, imported data (that describe a reference surface, for example). The parameter may be modified later, and the model will update to reflect the modification. Typically, there is a relationship between parts, assemblies, and drawings. A part consists of multiple features, and an assembly consists of multiple parts. Drawings can be made from either parts or assemblies.

Example: A shaft is created by extruding a circle 100&nbsp;mm. A hub is assembled to the end of the shaft. Later, the shaft is modified to be 200&nbsp;mm long (click on the shaft, select the length dimension, modify to 200). When the model is updated the shaft will be 200&nbsp;mm long, the hub will relocate to the end of the shaft to which it was assembled, and the engineering drawings and mass properties will reflect all changes automatically.

Related to parameters, but slightly different, are [[Constraint (computer-aided design)|constraints]]. Constraints are relationships between entities that make up a particular shape. For a window, the sides might be defined as being parallel, and of the same length. Parametric modeling is obvious and intuitive. But for the first three decades of CAD this was not the case. Modification meant re-draw, or add a new cut or protrusion on top of old ones. Dimensions on engineering drawings were ''created'', instead of ''shown''. Parametric modeling is very powerful, but requires more skill in model creation. A complicated model for an [[injection molding|injection molded]] part may have a thousand features, and modifying an early feature may cause later features to fail. Skillfully created parametric models are easier to maintain and modify.  Parametric modeling also lends itself to data re-use. A whole family of [[Screw|capscrews]] can be contained in one model, for example.

=== Medical solid modeling ===
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Modern [[computed axial tomography]] and [[magnetic resonance imaging]] scanners can be used to create solid models of internal body features called [[voxel]]-based models, with images generated using [[volume rendering]]. Optical [[3D scanners]] can be used to create point clouds or polygon mesh models of external body features.

Uses of medical solid modeling;
* Visualization
* Visualization of specific body tissues (just blood vessels and tumor, for example)
* Designing [[prosthetics]], [[orthotics]], and other medical and dental devices (this is sometimes called [[mass customization]])
* Creating [[polygon mesh]] models for [[rapid prototyping]] (to aid surgeons preparing for difficult surgeries, for example)
* Combining polygon mesh models with [[Computer-aided design|CAD]] solid modeling (design of hip replacement parts, for example)
* Computational analysis of complex biological processes, e.g. air flow, blood flow
* Computational simulation of new medical devices and implants ''in vivo''

If the use goes beyond visualization of the scan data, processes like [[image segmentation]] and [[image-based meshing]] will be necessary to generate an accurate and realistic geometrical description of the scan data.

===Engineering===
{{Unreferenced section|date=January 2012}}
{{Main|Computer-aided engineering}}
[[File:Cobalt Properties window.png|frame|right|alt=Property window outlining the mass properties of a model in [[Cobalt (CAD program)|Cobalt]] | Mass properties window of a model in [[Cobalt (CAD program)|Cobalt]] ]]
Because CAD programs running on computers "understand" the true geometry comprising complex shapes, many attributes of/for a 3{{nbhyph}}D solid, such as its center of gravity, volume, and mass, can be quickly calculated. For instance, the cube with rounded edges shown at the top of this article measures 8.4&nbsp;mm from flat to flat. Despite its many radii and the shallow pyramid on each of its six faces, its properties are readily calculated for the designer, as shown in the screenshot at right.