Cad Guidebook: A Basic Manual for Understanding and Improving Computer-Aided Design (60 page)

Firewall
A computer program that monitors the data and/or network traffic that
is being received by a computer (particularly servers) and tries to identify mali-
cious code or unauthorized access. It is a basic security procedure that may also
be bundled with scanning. Scanning may be looking for specific file names (such
as MELISSA), file types (such as VBS), strings of binary data (often called foot-
prints). These files are expected to be quarantined and/or destroyed and not
passed on to other systems or users.

First Angle Projection
A standard for indicating where views are placed on a
drawing. In First Angle, the Right View of the object is placed on the left of the
primary or Front View. This is the standard in European countries; Third Angle is
used in the United States.

Flat Pattern
2-D geometry that is cut from a flat plate, where the flat plate will
eventually be bent into another shape. The Flat Pattern has to account for the
growth of material in the flat form versus the bent. This is actually related to the
location of the neutral axis surface within the part that is between the inner and
outer face of bends. CAD systems which have the functionality to create sheet
metal parts should have the ability to create Flat Patterns. This can save a signifi-
cant amount of time and calculation in getting parts manufactured.

Floating Point Calculations
Calculations based on numbers that are not inte-
gers. For instance, calculating the area of a circle involves the number pi
(3.14159...). pi is a floating point number. Floating Point Calculations are per-
formed quite differently from integer calculations (such as adding 314 and 159).
Floating Point Calculations take the computer system much longer, particularly if
the numbers use high precision (such as 14 significant digits or a number such as
6.2940129993456). A CAD system (and even more so a CAE system) uses a
great deal of Floating Point Calculations; therefore the computer system must
perform well for this type of calculation.

FLOPS
A measure of performance for Floating Point Calculations; it repre-
sents the number of Floating Point Calculations that can be performed per sec-
ond. A VAX minicomputer from the early 1980s generally performed 1 million
FLOPS, or a MegaFLOP. Sometimes, the performance of that VAX system is
used as the basis for a standard MegaFLOP. A PC using the 80486 CPU and 66
MHz clock speed could also be similar to a MegaFLOP. Obviously, systems are
far beyond this performance now. Indeed, almost any computer generally has the

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Floating Point performance needed for a midrange CAD system. However, CAE
systems continue to demand as much performance as is available.

Folder
A logical partitioning of a Storage system (such as a Disk Drive). Dif-
ferent folders usually contain different types of files. A program file folder would
contain files for programs loaded on the computer system, for instance. This is
basically the same as a directory.

Fonts, Line
The type of line shown in a drawing. A solid line is a Line Font; a
dashed line is another Line Font. However, in a drawing, the Line Font also has mean-
ing for the representation of the object. A solid Line Font indicates a visible edge; a
dashed Line Font indicates a hidden edge (thus it may be called the hidden font).
Font, Text
A lettering style (similar to styles found in word processing soft-
ware). However, in a CAD system, the Text Font is usually constructed from sim-
ple lines and arcs; so many fancy fonts that would be found in a word processor
are not used.

Format, Drawing
The standardized border or layout of drawings. It is the in-
formation and structure that all drawings for a company are expected to have.
The specific geometry and documentation for an object is then placed within the
confines or border of the format. The Drawing Format would include compo-
nents such as the Title Block, Revision Block, Zone indicators, etc. ASME
(ANSI) and ISO standards are available for standardizing of Drawing Formats.
FORTRAN (FORmula TRANslation)
A computer programming language.
Its primary function is for programming engineering and scientific calculations.
Obviously, this can apply to many functions of a CAD system. However, a CAD
system is also even more dependent on computer graphics and user interface pro-
gramming, so it is typically not used for most CAD system programming (al-
though specific calculation functions within the CAD system may still use
FORTRAN). User-written programs that perform only calculations (and little or
no user interface) still may use FORTRAN. The input data for the program may
be created interactively, and the results of the analysis may be shown graphically,
but often these functions are simply performed by distinct computer programs
that are in a more suitable language such as C++ (these other programs being
called Preprocessors and Postprocessors respectively).

Frame Buffer
A final stage in a long set of calculations needed to create com-
plex computer graphics on a monitor. The Frame Buffer is Memory (RAM)
where individual Pixels on the monitor have an equivalent bits or Bytes of mem-
ory assigned to it. If multiple Frame Buffers are used, and the monitor quickly
switches between them, then computer animations can be accelerated. Although
it is a simplification, other terms for this component of a Graphics Adapter would
be video buffer or page buffer.

Free Edges
An edge in a 3-D model that does not meet and stitch up to any
other edges of other surfaces. This indicates a model which is not solid. In a solid
model, all the surfaces meet so that a specific volume is bounded or trapped.

298 Glossary

Free-Form
Pertains to geometry that is quite arbitrary. A Free-Form surface is
one that is sculpted (such as a car body panel). A Free-Form CAD system or
other modeler software would work with Free-Form surfaces without being lim-
ited to geometry or constraints that are sketched on a plane.

GD&T (Geometric Dimensioning and Tolerancing)
A system of symbols
and values that indicate specific accuracy of the geometry shown for an object.
Although a standard dimension can indicate a distance between two features of a
part (and a number of decimal places for precision), GD&T can indicate such
behaviors as perpendicularity, alignment,
parallelism, etc. GD&T should be able
to create a more accurate part that more carefully meets the need of the design.
ASME Y14.5M is the GD&T standard for the United States.

General Arrangement (GA)
Shows the highest level of design for a product.
It shows the product as it would appear in the field. It is often used as a basic
reference for the product (as opposed to a drawing that manufacturing would
build to). A 2-D representation of this would be a General Arrangement Drawing.
A similar concept would be a final, final assembly, or top level drawing.
Gouraud Shading
A common process or algorithm for displaying 3-D models
in shaded mode (where the model looks real). This algorithm is assumed to make
each surface of the part shaded as if it was the only surface shown. For instance,
there would be no shadows from one surface to another. This may seem less ac-
curate, but it is beneficial to the CAD system. It allows the total model to be seen
and worked on more easily.

Graphics Adapter
The device in a computer system that provides the com-
puter graphics data for display on the Monitor. The CAD system contains the true
size and characteristics of the objects. In order to see them, the CAD system uti-
lizes the Graphics Adapter to approximate, rasterize, manipulate, etc. the model
as shown to the user. There are many calculations that need to be performed by
the Graphics Adapter; therefore, the more that the Graphics Adapter does (using
coprocessors), the less the CAD system and the main CPU need to do, and the
faster the system’s performance. The Graphics Adapter can also be known as the
video adapter, graphics card, video card, etc.

Group Trapping
See Selecting

Groupings
A set of 2-D entities that are combined as a unit. This allows the set
of entities to be instanced (re-used), moved, rotated, scaled, exported, etc. In dif-
ferent CAD systems this capability is referred to as blocks, clumps, symbols, etc.
GUI (Graphical User Interface)
Interaction with a computer system based on
graphics instead of based on typed commands. Windows and Xwindows are ex-
amples of a GUI. However, Windows is not only the GUI, but the overall operat-
ing system. Xwindows is just a GUI, with unix being the usual operating system
that accompanies it.

Hexadecimal
Refers to a number system with the base of 16. This number sys-
tem goes from 1 to 9, and then uses letters for the 10th, 11th, 12th, 13th, 14th,

Glossary 299

and 15th numbers (A, B, C, D, E, and F respectively). Thus a 10 in Hexadecimal
is the number 16 in “standard” decimal numbering. Hexadecimal is very valuable
for dealing with binary data in a compact form. In order to prevent confusion
with standard numbers, Hexadecimal number may have prefixes such as &H or $.
Thus, $10 would be distinguished from 10.

Hollerith Data
An archaic reference to Character Data. The FORTRAN pro-
gramming language known as Fortran-66 used an H as a prefix for Character
Data with a number before the H indicating the length of the Character Data (or
string). Thus, 7HSCHOONY would be recognized by the system as the string
“SCHOONY.” Some neutral CAD files still use this method.

HPGL (Hewlett-Packard Graphics Language)
A plot data format that was
used by H-P’s pen plotters (which were very popular for CAD systems before
laser printers). It was a de facto standard for pen-based, vector CAD data for plot-
ting. Many laser-type printers can still accept this format through emulation.
HPGL, however, would only be appropriate for CAD drawings (not 3-D models).
HP-UX
Hewlett-Packards version of the unix operating system.

HTML (Hyper Text Markup Language)
The most basic format for web
pages. It indicates what text and graphics is shown on the page, where to locate
them, the font to use, etc. It is one of the languages that a web browser uses.
Probably its most valuable capability is the hyperlink, where a user can click on
the web page and go to other pages that are relevant to the user. This is an excel-
lent capability for ancillary materials for a CAD system such as on-line help,
documentation, and tutorials.

IC (Integrated Circuit)
The basic, digital technology that functions in a com-
puter system. The electrical circuit components (millions of them) are etched
onto wafers of silicon. They are often referred to as chips. Examples of ICs
would be the CPU, RAM, ROM, graphics coprocessors.

Icon
A small graphical image that symbolizes a program or option in a com-
puter program. They are clicked on, selected, or opened to have the program per-
form a function. They appear in the GUI of operating systems (click on an icon to
start a program such as a CAD program) and in the user interface of CAD pro-
grams (in an icon panel).

I-DEAS™ A high-end CAD system that was sold by a company called SDRC.
It was also available on IBM mainframes as a system called CAEDS. In the
1990s, it was totally reorganized as a system called I-DEAS Master Series. This
CAD system had a somewhat unique level of integration between a FEA program
and the 3-D CAD modeling. It also used a rather sophisticated set of database
tools to manage the 2-D, 3-D, FEA data.

IGES
A CAD neutral file. It can be used for 2-D (drawings) as well as 3-D
(models). It can contain data for a wide range of geometric entities, therefore.
However, a 3-D IGES file can be considered a file with just 3-D trimmed surfaces
(but not solid models). IGES stood for Initial Graphics Exchange Standard.