Originally software for CAD systems were developed with computer language such as Fortran, but with the advancement of object-oriented programming methods this has radically changed. Typical modern parametric feature based modeler and freeform surface systems are built around a number of key computer programming language modules with their own APIs1. A CAD system can be seen as built up from the interaction of a graphical user interface (GUI) with NURBS2 geometry and/or boundary representation (B-rep) data via a geometric modeling kernel. A geometry constraint engine may also be employed to manage the associative relationships between geometry, such as wireframe geometry in a sketch or components in an assembly.
Advanced capabilities of these associative relationships have led to a new form of prototyping called digital prototyping. In contrast to physical prototypes, which entail manufacturing time and material costs, digital prototypes allow for design verification and testing on screen, speeding time-to-market and decreasing costs. As technology evolves in this way, CAD has moved beyond a documentation tool (representing designs in graphical format) into a more robust designing tool that assists in the design process.
Today most CAD computer workstations are Windows based PCs. Some CAD systems also run on one of the Unix operating systems and a few with Linux. Some CAD systems such as QCad3 or NX provide multiplatform support including Windows, Linux, UNIX4 and Mac OSX5.
Generally no special hardware is required with the exception of a high end OpenGL based Graphics card. However for complex product design, machines with high speed (and possibly multiple) CPUs and large amounts of RAM6 are recommended. CAD was an application that benefitted from the installation of a numeric coprocessor especially in early personal computers. The human-machine interface is generally via a computer mouse but can also be via a pen and digitizing graphics tablet. Manipulation of the view of the model on the screen is also sometimes done with the use of a spacemouse/SpaceBall. Some systems also support stereoscopic glasses for viewing the 3D model.
1API – Application Programming Interface – интерфейс прикладного программирования;
2 NURBS – Non-Uniform Rational B-Spline – неоднородный рациональный В-сплайн (алгоритм компьютерной графики, используется в МП);
3 QCAD – двухмерная система автоматизации проектных работ (САПР);
4UNIX – сетевая операционная система. Большинство серверов Интернета работают под управлением UNIX или UNIX-подобных операционных систем, например, Linux;
5 Mac OSX – операционная система для компьютеров Macintosh;
6 RAM – Random Access Memory – оперативное запоминающее устройство (ОЗУ); запоминающее устройство с произвольной выборкой; оперативная память.
Дата добавления: 2015-09-10; просмотров: 9 | Нарушение авторских правCOMPUTER-AIDED DESIGN | UNIT II | Silicon Optics Aims to Combine the Best of Both Worlds | IX. Read the following statements and say whether they are true or false . Correct the false ones. | V. Find 1 or 2 sentences which we can omit as inessential in each logical part. | Magnetic Resonance Imaging | VI. Read the text and name the key points raised in it. | Clinical Systems | IV. Say where the information presented in the text can be used. | Physical Information Security |