



3D
Sculptor 
3D
Sculptor  a professional CAD engineer who uses Surfacing;
also known as Surfacing Engineer 
acceleration 
the
rate of change of the slope of a curve or surface. An arc, which has
constant curvature, has
zero acceleration. 
antitangent 
not a real word,
but "antitangent" is sometimes used in
modelling circles to describe two surfaces that are tangent to each
other but meet at a cusp (a sharp
edge). ie. they are 180 degrees from tangent. 
arc 
a
segment of a circle. Arcs are primary building blocks
for curves and surfaces. 
aspect
Ratio 
describes
the proportions of rectangular type shapes. A square has a low aspect
ratio (1:1). A long plank of wood has a high aspect
ratio 
base
Feature 
in
CAD construction this describes one of the primary features onto which
more detailed construction is then added. At the end of the model
build there may be little left of the base feature
even though it may still be recognizeable. 
beltline 
an
automotive design term describing the waistline of the car. 
bevel 
the
inclination between 2 surfaces when they are not at 90 degrees. 
bezel 
a mostly decorative
part surrounding an important element of a device. A bezel
is often a metal or plastic band that both covers a gap between 2
parts and also adds a finishing touch to the design. Examples could
be a watch bezel or the trim around the display on
a TV or the decorative chrome around the lights on a car. 
bezier 
a bezier
curve is a parametric, polynomial curve popularized by Monsiour
Bezier who made car bodies. Most commonly, they are quadratic
and cubic mathematical expressions. 
blend 
a
surface that transforms, or "blends", from
one section to another. 
blister 
a
tight, convex, bulbous form
that grows out of a larger base surface. 
boolean 
British
mathematician, George Boole, invented boolean algebra
with which all computers operate. A boolean union
combines 2 geometric forms. A boolean subtraction
removes one 3D form from another. 
bounding
box 
the
smallest rectilinear box into which a 3D feature, model, or assembly
will fit. 
Bspline 
a Bspline
or "Basis spline" is a parameterized spline
curve related to a Bezier curve. 
bulge 
I
think you know what a bulge is. A bulge
is most likely to be a soft form with continuous border where it meets
the base feature. Remember it is the base surface that is bulging
out rather than a discrete protrusion that is being added on. 
CAD 
Computer
Aided Design. Software such as Unigraphics, Catia, or Pro/Engineer 
CAD
monkey 
anyone
(almost exclusively male) who uses CAD 
chamfer 
an angled surface
created by sweeping a straight line around the outside edge of a part. 
character
line 
a crease in
the bodywork on the side of a car to create interest. Same as swageline. 
chine 
a chine
is a hard or soft edge between 2 surfaces on a boat that run down
the length of the hull. One can have one, two, or three chines
depending on the construction. Chines origininated
because of construction limitations rather than performance. When
using rigid, planar material such as plywood, where two boards meet
there will frequently be a hard edge. 
chord 
a straight line
drawn through 2 points on the circumference of an arc or circle. 
chord
length 
when creating
a tesselated file for export, one typically has to specify the maximum
chord length which effectively becomes the maximum
width of each facet. 
class
A surfacing 
a poorlydefined
term that relates to the quality of surface construction. Mostly associated
with the automotive industry, it stresses the avoidance of imperfections
when creating large, glossy, nontextured surfaces. Many people associate
class A surfacing with curvature continuity. 
closed
quilt 
a continuous
quilt or surface that contains a fixed and defined volume and has
no openings can be described as a closed quilt. A
solid can be created from a closed quilt. 
coke
bottle 
distinct
modified hourglass shape
in which the upper part is smaller and has a smaller diameter than
the main lower part of the bottle. 
concave 
a
curved, "hollow", surface where the surface
normals point towards each other such as the inner surface
of a sphere. 
cone 
a cone
is a fundamental 3D building block like a sphere or a cube. A cone
is an example of a "ruled surface". 
conic 
a
curve that is created by intersecting a cone with a plane. Possible
examples are hyperbola, parabola,
ellipse and a circle. 
construction
history 
history
is a element of parametric CAD programs that enable an engineer to
redefine, reorder, and evaluate individual features that have been
created to construct a model. Programs which don't have history
force the user to reconstruct the model when making most significant
changes. 
contiguous 
you can use
this word to describe things other than 48 American states. Contiguous
simply means unbroken, connected or continuous. 
continuity 
continuity
can refer to positional continuity
(G1), tangency (G1), curvature
continuity (G2) and higher. The greater the continuity,
the less noticeable will be the point or boundary between two curves
or surfaces. 
contour 
a contour
is mostly used to describe in 2D the form of a 3D body. It really
just means the outline of something. With a contour
map, this outline is created by intersecting a flat plane with the
3D geometry. 
control
vertex CV 
a control
vertex is the "handle" of a Bspline
that enables a user to manipulate a parametric curve. A single span
for a cubic Bspline will
have 4 CV's. 
convex 
the opposite
of concave. A convex
surface is curved in three dimensions such that the surface normals
point away from each other. An example would be the outer surface
of a sphere. 
cookie
cutter 
an extruded
cut made in a surface is sometimes described as a "cookiecutter". 
COS
curve on surface 
many CAD packages
provide the ability to create and modify a curve that is entirely
on an existing surface. This method can be compared with creating
a two dimensional curve and then projecting it onto a surface. 
crease 
a precise, smooth
bend in a piece of sheetmetal similar to a crease
in a piece of paper. Creases are created in a press
by a simple or progressive die. 
crown 
a "crown"
or "crowning" is the addition of convex
curvature to a protrusion (like the crown of the head). 
cubic 
an equation
to the third degree is described as cubic. They are
more flexible than second degree curves which are called quadratics.
Incidentally, if you are researching for the the arkbuilding trade,
a cubit is 18 inches or 45.72 cm. 
curvature 
the degree by
which a nonlinear or surface curves. A straight line or plane has
zero curvature. The smaller a radius, the greater
the curvature. 
curvature
continuity 
two surfaces
that are curvature continuous (G2) have the same
value of curvature across their common boundary. A curve or surface
that has curvature continuity also has positional
and tangency continuity. 
cusp 
a cusp
is a sharp edge on a surface that may be a modelling defect and will
probably be difficult to mould or machine. Think of a cusp
as the tip of an ocean wave that is about to break. Strictly speaking,
the two surfaces that meet at the cusp should be
tangent (antitangent)
to each other. 
cutline 
this is used
mostly in automotive circles to refer to the line or gap around openable
parts of the bodywork such as the doors, bonnet, and boot. Also called
splitline 
datum 
a fixed reference
feature such as a plane, axis, or point 
deboss 
not a proper
word. Don't use this in public. Deboss is used as
the opposite of emboss. A deboss
is created when a surface is lowered locally in a predefined shape.
They are frequently associated with the creation of a logo or pattern
on the surface of plastic 
dog
leg 
an element of
a design that resembles the back leg of a dog. For example, the distinctive
line of a BMW "C"pillar. 
draft 
an american
spelling variation of draught 
draught 
the beveling
of a surface in a constant direction in order to make it mouldable.
Depending on the material, texture, and geometry, a minimum angle
will be required for all surfaces in order to injection mould or cast
the part. 
ellipse 
an ellipse
is a type of conic section which
resembles an oval. An ellipse can be defined by a
major and minor diameter. In CAD, a partial ellipse can usually be
constructed that is basically a quarter of an oval. Here, apart from
the beginning and end points, the ellipse is defined by start and
end angle vectors and a rho value. Rho varies between 0 and 1 where
0 would be a straight line and 1 is a sharp corner. A pure ellipse
has a rho value of 0.414 
emboss 
to raise the
surface locally in a predefined shape for decorative (logos, etc)
or functionally (bosses, etc) effect. Designers also tend to use "deboss"
for the opposite of emboss. 
engrave 
if you cut your
girlfriends name into the bark of a tree you are not only a sap and
a vandal, but also an engraver. Engravers
typically work in the jewellery field. An engraved
feature could also be described as a "debossed" feature. 
exercise 
same as "flex" 
extend 
an extension
of an edge of an existing surface that is at least tangent
or curvature continuous
is called an extend. 
extrusion 
if you take
any two dimensional shape and and translate this shape normal to the
plane of the sketch, you will have an extrusion.
This is the most fundamental feature in CAD and is no different than
using a shape cut into a die to make a plastic or aluminium extrusion. 
fade 
a way of describing
a surface feature that is quite pronounced at one point and then fades
to a smaller or softer form or indeed disappears alltogether. 
fair,
faired, fairing 
a fairing
is the streamlined, fibreglass shell that makes a motorcycle faster
and more slippery to the wind. It is also the process by which spline
curves are smoothed out or "faired" to
make them softer. You are most likely to "fair"
a curve or surface digitally. People that build surfboards or wooden
boats often do their fairing manually. 
faceted 
a model that
is "faceted" is comprised entirely of triangular
or rectangular faces. This way of creating or saving data is very
useful for several applications such as rendering, rapid prototyping
and finite element analysis. 
fascia 
a zone
that is probably planar typically on the front of a product or component
that is frequently used for decoration or logos or to mount controls
or instrumentation. 
feature 
virtually all
created entities in the CAD world can be described as "features".
They don't need to be geometric features. They could
also be datum features. With parametric, historybased,
CAD, each feature will be a seperate entity in the
model tree. 
fillet 
a fillet
is the addition of material at the intersection of two surfaces in
order to make a smooth, tangent
connection. A fillet always adds material, whereas
a round removes material. 
flex 
in parametric
CAD circles, flexing the model means ensuring that
the part is robust by changing dimensions or parameters and checking
to see that it doesn't fail. This is very important if you work in
a large corporation and many other people will be working on your
part. It is extremely important if your part will be modified and
saved so as to create a family of similar parts. 
flow 
flow
is an important attribute to many industrial designs. Frequently,
surfaces must be seen to flow seamlessly around the
product without irregularities such as pinching or puckering. 
flush 
a surface that
is in line with another surface is flush (they both
protrude by the same amount). 
freeform 
freeform
surfaces are complex surfaces such as NURBS
that have been manipulated by pulling on CV's. They are not parametric. 
G0
continuity 
see positional
continuity 
G1
continuity 
see tangency 
G2
continuity 
see curvature
continuity 
gaussian
analysis 
gaussian
analysis evaluates the gaussian curvature
of a surface. This curvature
can be positive (for convex
objects like a sphere), zero (for ruled surfaces), and negative (for
concave surfaces). 
geometric 
geometric
forms are comprised of geometric elements such as rectangular extrusions
and spheres, etc. Contrast geometric shapes with
organic ones. 
hard
points 
hard
points are used to represent the location of critical elements
in the design around which everything else will be layed out or designed.
In many cases, these hard points will actually be axes, planes, etc. 
hourglass 
you can use
the word hourglass to describe not only your favourite
girlfriend but also some product designs. Another option is "peanut"
but your girlfriend may not be so keen on that one. 
hybrid
modeller 
a hybrid
modeller combines the functionality and advantages of surface
modelling and solid modelling. 
inflection 
an inflection
is a point on a curve where the curvature
changes from one direction to another. For example, the profile of
a wine glass will have an inflection point where
it changes from concave to
convex. 
iges 
Initial Graphic
Exchange Specification. A neutral data exchange format that uses ASCII
to define geometry in order to transfer it to another CAD program
(for evaluation or machining, etc). IGES was defined
in 1980. It has largely been superceded by STEP. 
interpolation 
interpolation
is figuring out the intermediate values inbetween the values that
you are sure about. When you create a curve or surface, your CAD program
will interpolate the necessary values between the points and curves
that you provide. 
isoline 
an isoline
is a curve that connects all the points on a surface that have equal
values. If the value is height, then isolines are the same as geographical
contour lines. 
isoparm 
short for "isoparametric
curve". By definition its any curve running across the entire
width of a nurbs surface that
is parallel to either the u or v direction of the surface. In reality,
isoparm is used to refer to any visible internal
curves on a surface or quilt. ie. any curves that aren't edge boundaries.
These internal curves are created when one of the boundaries on a
4 sided surface is comprised of 2 or more curves. 
knot 
as
you know, each spline is comprised
of a number of pieces each of which are defined by a polynomial. Between
each of these pieces is a "knot". 
lathe 
a lathed
surface is one that has been revolved (on a lathe) around a fixed
axis. 
lattice
structure 
one
approach to surface model building is to create an elaborate network
of interconnected curves that are then used to create boundary surfaces.
Some people use "lattice structure" to
refer to this curve network. 
linear 
linear
refers to a straight line (geometry) or a uniform rate of change of
function. ie. something that increases or decreases in a constant
fashion rather than the accelleration or decelleration that would
be the result of using a quadratic
or sine function, etc. 
loft 
a loft
is a type of surface construction. Lofted surfaces smoothly connect
2 or more curves in a continuous fashion. In Alias a loft
is called a skin. In Pro/Engineer
it is called a Blend. 
match
surfaces 
when creating
surfaces, there is frequently an option or necessity to join the new
surface to existing geometry. A surface can be "matched"
to its neighbour with either positional,
tangent, or curvature
continuity. 
merge 
a merge
is a boolean union between
2 surfaces. 
nacelle 
This is a nice
word that has its origins in the Latin word for boat. Today, it is
mostly used to refer to the streamlined enclosure for an aircraft
engine. Nacelle also is used for any kind of bump, blister, or housing
that houses the crew on a hot air balloon, aircraft, or dirigible.

nurbs 
Nurbs
are a specific mathematical definition of a curve or surface. Nurbs
stands for nonuniform rational Bsplines,
where the "B" refers to Monsiour Bezier.
Bezier was an engineer at
Renault in the 1950's and also a clever bastard. Nurbs
are defined by their order (mostly 1,2,3 or 5), their control points
(points in space that can be dragged around), and knots
(these provide control on how much the control points influence the
curve). 
obround 
A 2D shape that
is a combination of oblong and round. Its basically 2 straight, parallel
lines connected by 2 semicircles at either end. Another word for
obround is racetrack. Obround
is most frequently used in the world of sheetmetal punches where they
are used to provide clearance holes for bolts. 
ogee 
A shape where
a convex curve flows into a
concave curve. This form
is most commonly found on architectural details such as crown moulding. 
organic 
organic
surfaces tend to be smooth, soft, and flow together seamlessly, possibly
resembling forms found in nature. They may also be asymmetrical or
blobby. One might say that the opposite of organic
is geometric. 
oval 
A generic term
for an eggshaped form. It is not well defined like an ellipse
and can refer to a variety of symmetrical and asymmetrical (eg. eggs)
shapes. 
overbuilt 
A construction
technique whereby surfaces are created that are larger than necessary.
This ensures that there will always be a clear intersection line when
trimming or merging (surfaces
that are built linetoline may run into tolerance related failures
when merging). It also makes
the model more robust in the sense that it can be scaled up during
future design changes with less chance of failure. 
ovoid 
something that
looks like an egg. 
parabola 
A "U"
shaped conic section that is
frequently found in natural forms. An path of an object, such as a
cricket ball, thrown in the air can be defined by a parabola. 
patch 
the smallest
element of a nurbs surface is
a patch. 
perforated 
something with
lots of holes in it. 
pillow(ed) 
a pillowed
surface is one that is plumped up (like a pillow). Same as a crowning
except that pillowing is almost exclusively associated
with 3D whereas crowning can refer to 2D. 
pip 
a pip
is often used to define a tiny geometric bump on a surface. An example
might be the pip for blind people found on the number 5 key of most
cellphones. 
pivot
direction 
in Pro/Engineer,
the pivot direction was a term used to describe a
type of variable section sweep. The section being swept was always
aligned with the pivot direction. It is now called "normal to
projection". I used to think of an upright soldier squarebashing
and pivoting on one foot when making a turn. His body is the constant
normal or pivot direction with respect to the ground.
I'm sure that's not what they had in mind. 
positional
continuity 
this is the
lowest level of continuity. Two curves or surfaces that are connected
at a point or along an edge, but are not tangent or curvature continuous,
have positional continuity (G0). 
proud 
a surface that
protrudes more than its neighbour can be described as proud.
Compare with recessed and flush. 
punched 
a solid or surface
that has an extruded cut made through it, can be described as punched.
Same as cookiecutter. 
quadratic 
A secondorder
equation. 
racetrack 
A rectangular
shape with a fullround at both ends. Same as obround. 
rail 
A rail
is a trajectory along which a curve can be swept to create a 3D surface.
Such a sweep may have one or more rails. 
rake 
Rake
describes the angle at which something is designed with respect to
the vertical. For example, a streamlined car might have a heavily
raked windscreen. 
revolved
surface 
a surface that
is created by rotating a section around a fixed axis. 
ribbon 
A surface with
a short, straight, constant crosssection that sweeps along a 3D trajectory.
In surface construction, ribbons are often used as
structures to define tangency
for boundary surfaces. 
robust 
A 3D model can
be defined as robust if random features can be modified slightly without
the model failing. Making changes to verify robustness
is known as "flexing" the model. 
round 
a round
is the softening of an edge by the removal of material. The new surface
is tangent to the original two surfaces. If the edge is at the 90
degree intersection of two planar surfaces, the round
is a quarterround (a qudrant of a cylinder sliced longwise). Rounds
are normally circular in section, but some CAD programs also allow
for conic rounds. Rounds are similar
to fillets. 
ruled
surface 
a ruled
surface is one that can be produced by sweeping a straight
line along a trajectory. Planes, cylinders, and cones are examples
of a ruled surface. All ruled surfaces
have zero gaussian curvature.
An understanding of ruled surfaces is useful for
designing parts in sheetmetal. All sheetmetal parts that need to be
"developed" must be comprised of ruled surfaces
(in order to create a flat pattern). 
saddle
point 
the
point on a surface that is shaped like a horse saddle.
Seen from one direction the surface forms a "u". Seen from
another direction (at 90 degrees) it forms an "n". The form
can also be compared with the shape of a mountain pass. 
scan
data 
the mass of
point data that is created when an object is digitally scanned with
a laser scanner. This raw data is typically then processed to create
more useable file types, such as tesselated data or nurbs. 
scoop 
scoops
are air intake devices frequently found on the bonnet of cars. A scoop
can be used to describe many oriented inlets to a fixed volume. 
sculpt 
the act of adding
or removing material in real life with real materials or digitally
with Computer Aided Design 
shell 
a shell
is a wall of constant thickness. A solid that has its insides "consumed"
to create a thin wall is said to be "shelled
out" (think of a snail being removed from his/her
shell) 
skinning 
skinning
is another word for lofting which is creating a smooth, continuous
surface through 2 or more curves. The term "skinning" is
frequently used by Alias users. 
soft
point 
soft
points are points on a spline that reference existing geometry.
They are created by the user during construction of the spline
by selecting an edge or vertex. They are "soft" in the sense
that the spline will be forced to update when the referenced geometry
changes. 
solid
model 
in 3D CAD terminology
a solid model is once that has a finite closed volume
that can be measured. Any closed surface can be made into a solid.
Solids can be added to an subtracted from each other using Boolean
operations. When removing material from a solid, the part is cut whereas
for a surface it is trimmed. 
spline 
A 2D or 3D curve
defined piecewise by polynomials. The term piecewise simply means
that different polynomial expressions are used to define the curve
for different pieces or sections of the curve. A spline
is a simplified approximation of what might otherwise be a very complex
mathematical expression. A Bezier curve
is an example of a spline. The term "spline"
is borrowed from boatbuilding where it refers to a thin strip of flexible
wood (in East Anglian dialect). This wooden strip held between two
fixed points on what will become the ships hull assumes a smooth shape
in order to minimize the energy held in the wood. Wooden splines
were also used in the early days of aviation and automobile design. 
split
line 
the common line
or split between 2 adjacent components. See also cutline 
spoiler 
a spoiler
is an aerodynamic device that is attached to a car that may be used
to increase downforce by reducing the air going under the car or by
directing air by means of a wing type design. 
spun
surface 
see revolved
surface 
step 
Standard for
the Exchange of Product model data. STEP is an ISO
standard (ISO 10303) and is used to transfer model geometry data between
different CAD programs. STEP is a more robust alternative
to IGES. 
strake 
strakes
are two different but related things depending on whether you're discussing
boats or planes. For boats, they are the long planks of wood or steel
that run longitinally down the boat to create the hull. For a jet
plane, strakes are an extension of the wing that runs along the fuselage
of the plane to create improved aerodynamics. 
surface
modeller 
any CAD program
such as Rhino that models with surfaces. Naturally, it follows that
one uses a solid modeller to create and modify solids. Most mainstream
CAD programs such as Pro/Engineer and Solidworks are known as hybrid
modellers since they can function in a mixture of both
modes. 
surface
normal 
all points on
a surface have associated surface normals (normal
simply means a vector at 90 degrees to the direction that the surface
is going). It is typically more convenient to use the surface normals
rather than a surface tangent vector. The surface normal
is also used to define which of the 2 sides of any surface is the
positive one. This is akin to describing the inside and outside of
a surface. This (mathematical) information is used to decide what
happens when merging 2 surfaces
together. 
swage
line 
a swage
line is any raised styling line or crease on an automobile
such as the beltline. Some
time back, it was not possible to create an entire door from one piece
of sheetmetal. Instead, two stamped pieces were swaged (mechanically
joined through deformation) together to create a single part with
a raised line through it. 
sweeten 
to refine curves
in order to improve surface aesthetics. This may be a matter of eliminating
defects, improving smoothness or flow,
or simply adjusting the design. 
tangent 
two curves can
be described as being tangent at a given point if
they point in the same direction at that point. Surfaces that are
tangent to one another across a common boundary join
are joined together in a reasonably smooth manner. 
teardrop 
teardrop
can be used to describe a shape that is basically a triangular form
with a full round at each end. 
topdown 
the best way
of describing "top down" is to describe
the opposite which is "bottom up". If you start to build
a model by grabbing a bunch of Lego blocks and sticking them together,
this is "bottom up" where "bottom" is the smallest
part or feature in the model. If we start of by considering the space
claim and functional requirements of the toplevel of the assembly
or part we are designing, this is "top down"
design or construction. The lower level subassemblies and parts will
all be driven by this initial high level design. In practice, when
using CAD, these topdown considerations are controlled
by a single "master model" that defines that boundaries
of each part and the manner in which each part relates to its neighbour. 
transition 
a transition
is any region of variable geometry that, possibly a sweep or round,
that allows a various parts of a design to fit seamlessly together,
Unless you're designing a sphere or and Ipod, there's a good chance
that your model will be comprised of various distinct geometric regions.
These will be connected by transitions. 
trim 
when surfaces
are cut down to a smaller size, they are "trimmed".
A solid is cut. A surface is trimmed. 
tweak 
to "tweak"
is to marginally refine a feature so that it meets functional or aesthetic
requirements. 
Utah
Teapot 
the standard
3D reference model for rendering that was created at the University
of Utah in 1975. The teapot is useful because it
is a relatively simple model and yet looks very nice when rendered.
It also contains convex and
concave surfaces, saddle
points, and is selfshadowing due to the handle and spout. 
UV 
NURBS
surfaces are constructed in two directions like a grid. The two directions
are nominally called U and V. 
vertex 
a vertex
is a sharp point on a surface where two edges meet. 
voxel 
voxel
is the big brother of pixel. Whereas a pixel is the smallest element
in a 2D image, a voxel is the smallest element in
a 3D "scanned" image. 