Cad Guidebook: A Basic Manual for Understanding and Improving Computer-Aided Design (63 page)

Platform
Encompasses a computer system’s hardware, software, and peripher-
als. Some operating systems, in particular, can be used on different kinds of com-
puter hardware; therefore, platform can be a better distinguishing term than the
CPU or operating system for a CAD workstation.

Preprocessor
A computer program that works on data files prior to some more
significant operation. Many Compilers use a Preprocessor to condition source
code before doing the real compiling. A Preprocessor for a CAE program (such
as FEA or CFD) is used to prepare data to be analyzed. The Preprocessor activity
could, in fact, be more intensive than the calculations for the analysis; getting

308 Glossary

good results is often wildly dependent on the proper preparation of the input data
(i.e. preprocessing).

Postprocessor
A computer program that works on data files after a more sig-
nificant operation. In a Computer Aided Manufacturing (CAM) environment, a
Postprocessor translates the NC data from a CAM program to actual control
codes for a specific NC machine. In a Computer-Aided Engineering (CAE) envi-
ronment, a Postprocessor is used to view and analyze the large volume of results
from the run of an analysis.

Product Structure
A logical arrangement of information that is needed to
fully manufacture and/or assemble a product. It includes the Assembly Structure
to indicate what part models are needed in the assembly model, as well as non-
geometric information related to the assembly. A Bill of Material that includes
drawings, specifications, manuals, material specifications, etc. can be assumed to
fully define the Product Structure.

Pro/ENGINEER®
(often called just “Pro/E”)
A high-end CAD system that
is sold by PTC. It was probably the most instrumental system for the rise of 3-D
CAD systems in general.

Prototype
An evaluative model of a product. It is assumed to demonstrate
whether the product is practical or meets requirements. The most common type
of Prototype is a physical model of a product. A car manufacturer, for example,
may manufacture a new model of car just for test purposes. However, Prototype
may refer to other kinds of products such as logic systems or software.
Prototype Drawing
A drawing that is used as a template for other drawings
that are subsequently created in the CAD system.

RAM (Random Access Memory)
Made up of banks of memory chips (ICs).
Although RAM chips are used in a number of subsystems of a computer, RAM
often is assumed to be just the main Memory of the system that the CPU commu-
nicates with.

Rapid Prototyping (RP)
The technology related to the creation of physical
models based directly on 3-D CAD models. Rapid Prototype machines use the 3-
D CAD model data to guide computer-controlled material sintering or deposition
devices.

Raster Graphics
The type of graphics that has been broken down into discrete
elements. When a Monitor displays an entity (such as a circle), it has been raster-
ized. This was the process of taking the pure circle model (the center of the circle
plus a radius) and translating it into the appropriate series of Pixels to be turned
on on the Monitor. This type of graphics
would be different than Vector Graphics
(which does work with the pure data). There were computer graphics displays at
one time that relied on the use of oscilloscope-type, analog signals that would not
necessarily involve the rasterization process.

Raster-to-Vector
Techniques that attempt to convert Raster Graphics into Vec-
tor Graphics. This is similar to OCR technology.

Glossary 309

Ray Tracing
An advanced computer graphics technique that allows a 3-D
model to have effects like reflections. It involves an extremely large amount of
computation to trace virtual lines of light (or rays) as they go from the observer to
each surface on each object in a scene, and then it sees if the end of this process
ends at a light source.

Release
Indicates when a drawing or other engineering product is finished, ap-
proved, and shared throughout the company. A released drawing is one that is
available for vendors, manufacturing, etc.; while a drawing that is considered pre-
release is not available for use to these areas. Since the changes to the released
drawings may have to be made simultaneously, they are then often grouped into a
single event of release. The group of drawings is often referred to as a Drawing
Package, and the event may use such terms as Engineering Change Order (ECO)
or Engineering Change Notice (ECN) or Engineering Release Notice (ERN), etc.
Resolution
Indicates how refined or precise a device may be using a numerical
limit or capability. This is particularly true for Monitors. In this case, Resolution
is measured as the maximum number of Pixels that can be accommodated. For
intance, a Resolution of 1024 Pixels (in the X) by 768 Pixels (in the Y) is a higher
resolution than 800 by 600.

Revision Block
A set of notes on a drawing that shows the Revision Level of
the drawing and the past Revision history.

Revision Level
The current state of a drawing, part, Bill of Material, etc. Man-
ufacturers tend to avoid recreating designs and documentation (instead favoring
re-use). In order to handle the evolving nature of the items, Revision Levels are
applied and managed. It is usually a number or letter that is incremented as the
item is changed over time.

Revolve
A 3-D modeling technique whereby a set of existing geometry is re-
volved about an axis. A doughnut shape can be the result from revolving a circle
about a central axis.

RGB
The primary colors for emitted light—red, green, blue. Colors shown on
a Monitor are generated by varying the level or intensity of each of the constitu-
ents. RGB also referred to a type of connection between a Monitor and its Graph-
ics Adapter. These were special coaxial cables for the colors.

ROM (Read Only Memory)
ICs or chips that have information permanently
written on them (they are not read/write or Random Access). They are used for
functions that are static for the life of the computer system or component. For
example, if a Disk Drive needs to use some programming to help calculate the
location of data on the drive, this programming may be stored on a ROM chip
that is attached to the drive (instead of using up main memory).

SAT®
File
A geometry exchange file format for the ACIS kernel. SAT files
should be able to transfer 3-D geometry and data accurately between different
CAD systems that use the ACIS kernel.

310 Glossary

Scale
The relationship between a physical object and its appearance in a model
or drawing. In drawings, a view scale is a ratio between the physical object size
and the dimensions shown in the drawing. A Scale of 0.5 indicates that the 2-D
geometry in the view is half the size of the real object. Scale also refers to chang-
ing the size of a 2-D or 3-D model by some scale factor.

Screen Dump
The process of making a hard copy of exactly what is shown on
the Monitor. It is generally not used for drawings since they have precise paper
size and release issues. However, it is not uncommon for hardcopies of 3-D mod-
els to be done via a Screen Dump.

SDRC (Structural Dynamics Research Corporation)
The company that de-
veloped the I-DEAS CAD system. SDRC and I-DEAS are somewhat inter-
changeably used to refer to this CAD system.

Section View
A view in a drawing that is based on cutting through an object.
The cut object is shown with cross-hatching. They are identified by a letter, and
the path for the cutting is shown by a Cut Plane or Cut Line. A Section View that
uses a Cut Plane that starts and ends with a letter A would be identified as Section
View A-A.

Selecting
The identification of items that are available in the CAD system. This
may refer to Picking items on the Monitor; it may refer to Selecting from a list of
choices on a form or in a menu.

Server
A computer on a network that provides a capability or service for the
other computers on the network. The most common application would be the File
Server that provides files from a central location. Other types of servers would be
a print server or a license server.

Sewing Up
See Stitching.

Shading
The process of displaying 3-D models in realistic form. This involves
analyzing the surfaces in the 3-D model and the virtual light source and then
changing the colors (or shades) all over the surface to give the appearance of the
3-D nature of the model.

Shell
First, a technique that is used in 3-D modeling. Shelling adds a thickness
of material by projecting outwards (or in the normal direction) from the surfaces
in the 3-D model. Second, refers to the command processor used in unix com-
puter systems. The Shell is the program that is constantly monitoring the key-
board for commands that are typed by the user.

Shell Script
A file with commands to be run by the operating system (typically
a unix system, but it can generically be applied to other operating systems as
well).

Sizes
See Drawing Size.

Sketch
A simple 2-D drawing that is not expected to be released. It is typically
used by engineers or designers to document the basic geometry of the design.
This idea is adopted by 3-D CAD systems to refer to the creation of basic or
foundation 2-D geometry that forms full 3-D features. This Sketch is usually

Glossary 311

given the ability to have advanced geometric behavior (such as being constrained
or even animated).

Sketch Plane
The plane that is used to create the Sketch used for the basic or
foundation 2-D geometry that is needed for some full 3-D features. Careful selec-
tion and tracking of these planes is an essential ingredient of making full use of
features-based modeling.

Solaris®
Sun Microsystem’s version of the unix operating system.

Solid Edge®
A midrange 3-D CAD system that was bought out by Unigraphics.
Solid Model
A 3-D part model that bounds a volume. It is a normal part model,
in some respects. There are technologies that only use solid models, but most 3-D
CAD systems supply surface-based modeling as well. Indeed, these methods are
usually combined and invisible to the user.

SolidWorks®
A midrange 3-D CAD system that was bought out by Dassault
Systems.

Source Code
The real computer programming that software is built from. Files
that contain, BASIC, C, FORTRAN, Java, etc. that can be seen, studied, and
modified are examples of Source Code. Software vendors do not supply Source
Code; they supply object libraries or executables which customers can only run
(customers are unable to see how the software was actually created).

Spline
A geometric entity that can follow rather arbitrary paths. A wire or hose
that bends and turns is an example of something that can be modeled using a
Spline. A Spline was originally a long thin piece of plastic that could be bent to
create a smooth 2-D path on a drawing. The path was constrained by lead weights
(ducks or whales) with a thin wire that protruded from them to hold down the
plastic at specific points. The mathematics of Splines are related to Bezier Curves
(which use control points) and B-Splines. Sometimes, the tension of a spline re-
fers to how tightly the path follows the points. Splines are now available in 3-D as
well as 2-D.