This is a term which refers to the general case
of flat geometry, meaning that the geometry in question will lie
on a plane. Strictly 2D geometry means that only two of the three
coordinates [x,y,z] are saved and used. 2D, however, can also be
used to refer to a portion of three-dimensional geometry which
lies on a plane.

This is a term which refers to geometry that is
described using all three coordinate values [x,y,z]. All
geometric models of objects use 3D geometry to define their
shapes.

This is a somewhat arbitrary location defining
the mid-point of the boat. It usually is defined as one-half the
distance between the forward end of the waterline to the aft end
of the waterline. Since the forward end of the waterline is
usually placed at X=0 in the coordinate system, then the
amidships position is located at X = LWL/2. This amidships point
is important since it is the location where the draft is
measured.

This location is usually at the aft end of the
design waterline (DWL) or located at the rudderpost for large
ships.

Attribute is a term used to describe the
identifying features of an entity (point, curve, or surface).
Attributes of an entity include things like color, visibility,
and point type.

The baseline is the location where Z=0 in the
coordinate system. Normally, this is where the bottom of the boat
or the keel is located. During the design process, however, the
position of the keel may change, but the baseline is always at
the Z=0 position.

This is the maximum width of the boat at any
location along its length.

In naval architecture, this term is used to
describe a specific format for the section view of the boat. This
section view involves drawing the forward stations of a boat on
the right side of a vertical centerline, and the aft stations
flipped over and drawn on the left side of the centerline. The
amidships location is usually used to determine when to begin
flipping the sections over to the left side. This is done so that
the forward sections will not cover up the aft sections.

This defines a common edge joining two NURB
surfaces. Both surfaces must meet at that edge with exactly the
same number of defining points and the connection must extend the
full length of each surface edge. This is different from a merged
edge in that a single relationship entry is created for this
edge. Certain commands, like Add Row/Col will continue across a
bonded edge, but not a merged edge.

This is another term for a knuckle or knuckle
point, which is a hard or non-smooth change point along a curve.
On a chine-type hull cross-section, for example, the chine point
may be called a knuckle point or a breakpoint.

This is class of piecewise polynomials that is
used for curve and surface definition. The B stands for basis.
B-splines are mathematically defined using vertex control points,
which do not lie on the curve or surface.

This is the curve created by intersecting a
plane at a specific half-breadth (Y-value) with the hull
geometry. The curve can be seen in the profile view of the boat.

This is the maximum width of the boat measured
across a waterplane cut of the boat. Depending on the context,
this value may or may not refer to the beam at the design
waterline.

The centerline is the Y=0 location on the
coordinate system. It defines the global symmetry plane for the
boat.

The centroid (sometimes called a center of
gravity) of a bounded surface is the center point or middle point
of the area. Traditionally, this point is found by cutting the
area out of cardboard and balancing it on a pin. The balance
point location is the centroid.

This is a hard (not smooth) division line
between two surfaces located below the sheer line. For example,
most standard planing power boats contain at least one chine for
spray separation.

This term refers to the process of pressing and
releasing a mouse button. This is usually the left mouse button,
unless otherwise specified. A click is different than a pick,
because with a click operation, you are not necessarily selecting
an object or entity. The Add Point command, for example, requires
to to position the cursor where you want the point and click the
left mouse button to set the point.

In discussing B-splines or NURBS, a column is
one of the iso-parametric curves which define these surfaces.
"Rows" lie in a direction perpendicular to columns.
These surfaces are made up of a rectangular-like mesh of rows and
columns.

This term is often used interchangeably with
the term vertex point, because it is the point officially used by
a B-spline to define its shape. In this program, however, you can
use either the vertex point or a point on the curve or surface to
control its shape. Therefore, "control point" may be
used to refer to either a point on the curve or surface.

Many of the commands in this program will be
used over and over again in succession, like the Move Point
command. This program does not require you to reselect the Move
Point command each time you want to move a point, because after
the first menu selection, it becomes the current command and its
label is shown on the right side of the Status Line. For the Move
Point command, you simply pick and move the next point. The
current command remains in effect until another command is
selected.

The current plate is the hull surface selected
by the user for development. This is done using the Select Plate
command. For development, the plate must have either two rows or
two columns. Once a surface (plate) is current, you can display
its Layout View or its Layout Numbers.

This is a mathematically-defined term which
refers to the amount of roundness located at a point on a curve
or surface. If a curve is flat, then its curvature is zero. As
the curve becomes more rounded, the radius of curvature goes down
and the curvature goes up. Curvature 'k' = 1 / rho, where rho is
defined as the radius of curvature. These two values ('k' and
'rho') are inversely related.

This is the term used to identify those 3D
points that are used to define an entity. For a point entity,
there is just one defining point. For a curve, there are a series
or string of defining points, ordered from one end of the curve
to the other. For a surface, there are a grid or matrix of
defining points, located at the intersections of all defining
rows and columns.

This term refers to a relationship between two
entities. Some relationships, like Fix Pnt Rel Pnt, involve an
independent and dependent entity. The point that is fixed
relative to another is said to be dependent (form a dependency)
on the other point. If the independent point is moved, then the
dependent (relative) point moves along with it automatically.

This is a vague distance usually defined as the
distance from the bottom of the hull (without appendages) to the
highest point on the sheer line. If the program uses this number,
it is only for sizing purposes and need not be perfectly
accurate.

This term is used to describe hull surfaces
which can be easily constructed out of flat material, like
aluminum and plywood. Developable surfaces are combinations of
flat, cylindrical, and conical shapes. Mathematically, a
developbable surface is one where all points on the surface have
a Gaussian curvature of zero. In addition, one may use the
concept of ruling lines to define a developable surface.

This is the curve defined by intersecting a
plane diagonally through the bilge area of the hull geometry. The
curve can be seen in the profile or plan views. The diagonal
plane is defined by two values: its intersection height (Z-value)
on centerline and the heel angle of the plane.

This term refers to the process of tracing
lines into the compuer using a tablet or digitizer pad. For boat
design, this usually refers to taping a body plan to the tablet
and tracing each station into the computer, one by one. These
stations can then be fit or "skinned" with B-splines
surfaces. (See the Digitizer program.)

For this program, a document is the virtual
representation of a particular 3D view of the model. A document
view is created by scaling the 3D model view to the document
coordinates using the user-defined scale factor (e.g. 1 inch = 1
foot) and adding the user-defined margins. If the document is to
large to fit on the output device, it is automatically broken
into pages covering the whole virtual document.

This term refers to the process of pressing and
releasing a mouse button (usually the left) two times in a row,
in rapid succession. This is a common technique used by many
Windows programs for various purposes. It normally means that you
want to edit an object or to look at its attributes.

This is the distance from the baseline (Z=0) to
the waterline at amidships. Normally, draft is used to mean the
distance to the design waterline(DWL), but it often depends on
its context of use. In addition, the bottom of the boat is
usually located at the baseline so that draft refers to the
distance from the bottom of the boat to the waterline. However,
if the bottom of the boat is NOT located at the baseline, you
still must calculate draft from the baseline.

In reference to computer-aided design, drag is
process of moving points or objects in a computer program. The
process involves using the left button of the mouse to select
(pick) an object or entity and move (drag) it to a new position.
To begin the drag, use the left mouse button to select an object
(such as a point). While holding down the left button, move the
mouse to reposition the object. When it is in a desired location,
fix it there by releasing the left mouse button.

This is the length from the intersection of the
design waterplane at the bow, to the intersection of the design
waterplane at the stern. Often, people use just LWL, but DWL is
more specific.

DXF stands for Data eXchange File. It is a file
that contains simple geometry entities (like lines, polylines,
and text) that was created by AutoDesk, makers of AutoCAD. It has
now become a standard means for transferring geometry data
between CAD programs. These files are identified by their
".dxf" extensions.

This is a term used to refer to specific
geometric objects. Most all CAD programs use entities as their
basic unit of definition. For this program, the basic entities
are: point, curve (includes polylines and combination curve and
lines), and surfaces.

This is the process of manipulating the
definition of a hull shape to create a smooth surface for
construction. Traditionally, this has been done on a drafting
board using splines, ducks, and ships curves applied to stations,
waterlines, buttocks, and diagonals. By computer, this is done
using curvature analysis applied to the rows and columns of
B-spline surfaces.

This is a subjective, human term, which refers
to the smoothness of a hull surface. There is no mathematical
definition of fairness, although some define it as continuity of
the second derivative. This may be a necessary condition, but it
is not sufficient. A cubic B-spline guarantees second derivative
continuity, but can easily be unfair. A better definition relates
to the continuity of curvature of the curve or surface.

This is the position on the boat where X = 0.
Usually this is set to the forward end of the design waterline.

This is the curve created by intersecting a
plane at a specific transverse cut location (X-value) with the
hull geometry. Although this term specifically refers to a
structural member located at a particular transverse
cross-section, it is often used interchangably with term station.
The curve can be seen in the section view of the boat.

This term refers to the distance from the
waterline to the sheer line. Often, freeboards at very specific
locations are needed, in which case you have to be very careful
in determining exactly where and how the freeboards are measured.
Sometimes the sheer point is not well defined.

This is a mathematical term used to describe
the double curvature of a point on a surface. If a surface is
developable (flat in one direction), then the Gaussian curvature
is zero. As the surface becomes more curved in two directions
(twisted), the Gaussian curvature increases (positively or
negatively). Mathematically, the Gaussian curvature is the
product of the two principal curvatures.

For B-splines, this refers to a technique which
changes the shape of the curve or surface over the entire range
of the curve or surface. The change might be very small, but
there is no guarantee of no change. (see also local)

This term is used to describe the straight
lines drawn at the defined hull cut locations. These locations
are defined in the HullCuts pull-down menu section. Their dispaly
can be turned on and off using the Display Options dialog box,
located under Options.

The heel angle is the angle in degrees that the
waterline assumes with respect to the baseline of the boat.
Upright, the boat has a heel angle of zero. For the calculations,
the boat remains upright in the coordinate system and all
calculations are done with a heeled waterline. That way, all of
the numbers relate to the constant, upright coordinate system.

This is a generic term used to define a planar
cut of the B-spline hull surfaces. Since the rows and columns
that define the B-spline hull surfaces are not necessarily any of
the traditional lines (stations, waterlines, buttocks, diagonals,
and "other cuts"), then the program must calculate
their shapes by mathematically cutting the B-spline surfaces with
a plane. That is why the program often refers to the traditional
lines as hull cuts.

IGES stands for Initial Graphics Exchange
Specification. It is an ANSI standard file definition for
transferring 3D geometric data between CAD programs and allows
for a large variety of entities, especially NURB curves and
surfaces.

This term refers to the process of defining a
curve (or surface) that passes through a set of points.
Interpolation does not imply any one curve type or technique. It
can be applied to almost any type of curve or surface. For
B-splines, interpolation is a process whereby the program
calculates the control vertices for a curve or surface which pass
through the input defining points.

This term refers to a curve defined using the curvature values of a curve (or row or column), the normal vector to the curve (or surface), and a scaling factor. The K_curve is drawn by connecting the K_Curve points, which are defined as:

K_Curve Point = Point on curve + curvature*scale factor*normal vector

This curve magnifies the fairness of a curve
and is used for fairing curves and surfaces.

This term is used interchangeably with the term
VCG. The 'K' refers to the keel of the vessel, which for many
designs, is located at the baseline (Z=0). The 'G' refers to the
center of gravity point. Therefore, KG is the vertical distance
between 'K' and 'G', which is the same as VCG.

Refering to NURBS, a knot is a number which is
part of the definition of a B-spline curve or surface and which
is used to control its shape. The collection of all knots used by
a B-spline is called a knot vector. The distance between knot
values is called its knot spacing. Uniform B-splines set the knot
spacing to 1 (usually), and NURBS (non-uniform) allow for uneven
spacing of the knots.

This term refers to an abrupt or hard edged
change in the shape of a curve or a surface. The point at which
the hard change is located is called a knuckle point or a
breakpoint on the curve. For surfaces, a knuckle line or curve
usually forms the hard edge between two surfaces. (Most people
call this a chine!)

This is a term use to describe the process of
un-wrapping surfaces into their equivalent 2D shapes. It only
applies to surfaces that are developable.

This is the distance between the forward
perpendicular (FP) and the aft perpendicular (AP). It is usually
called LPP for large ships. For small vessels, this value is
usually equivalent to LWL..

This is the longitudinal X-position of the
center of the volume of the underwater portion of the hull. It is
calculated by the Hydro Calc command. It is referenced from the
forward perpendicular (FP at X=0). Be careful, because some texts
reference this value from amidships and some define it as a
percentage distance (of LWL) aft of the forward end of the
waterline.

This is the length of the boat from the tip of
the bow to the furthest point aft on the stern.

For B-splines, this refers to a technique which
changes the shape of the curve or surface only over a limited
range of the curve or surface. Outside of this range, the program
guarantees that the shape won't change at all. (see also global)

These are structural members which are attached
(welded, perhaps) to the hull and which run along the length of
the boat. They are often called stringers.

This is the distance from the forward
perpendicular (FP) to the aft perpendicular (AP). This is the
same as LBP, but this term is more common in the big ship world.

This is the distance from the intersection of
the waterplane at the bow, to the intersection of the waterplane
with the stern. Often, this term is used to mean the design or
target waterline length. See also DWL.

This defines a common edge between two NURB
surfaces, where all of the edge points of one surface have been
Merge Pnt To Pnt to all of the edge points of a second surface.
This is different from a bonded edge in that one merge
relationship is stored for each connecting edge point and no
commands will cross a merged edge boundary. For example, if you
add a row into one surface that runs into a merged edge, the add
row command will not continue into the merged surface.

Model can be used as a noun or a verb. A
geometric "model" is a 3D definition of an object such
that a program can use it to perform analyses (volumetric,
structural, etc.) and to create construction information
(templates, NC cutting instructions, etc.). To "model"
an object, refers to the process of defining the 3D shape of an
object.

For NURB surfaces, this term refers to the
allowable uneven spacing of the defining knot values (knot
vector). Knots are used in the definition of B-splines and can be
used to control their shapes.

This term refers to using data extracted from a
3D geometric model and sending it to a cutting machine (lathe,
mill, router, etc.) for automatic cutting of a part. For example,
you can take the 2D frame shapes and the 2D developed plate
shapes and transfer that information to an NC plasma cutter to
cut out the pieces from large aluminum sheets.

Non-Uniform Rational B-Spline. This is the most
general form of a B-spline commonly being used by CAD programs.
Non-Uniform allows uneven spacing of the B-spline knots for more
control over the shape of the curve or surface. Rational allows
for exact representation of conic shapes and simpler perspective
projections.

This term normally refers to [x,y,z] points
which define the intersection of waterlines and buttocks with
each station of the hull. These points can then be organized into
an "offsets table". X is the station location, Y is the
half-breadth, and Z is the height of the offset.

This is a unique term which refers to the
process of moving a point by a very small amount (an ooch
distance). With the Move Point command it is impossible to change
the shape by less than one pixel on the screen. Most programs
require you to zoom in until you have the resolution you need.
This is inconvenient for many tasks, so the ooch point command
was invented to allow you to move a point by a fixed distance,
which may be less than one pixel This command is very useful for
fairing.

This is the curve created by intersecting a
plane with the hull geometry. This includes all hull cuts not
covered by stations, waterlines, buttocks, and diagonals. Since
three points in space define a unique plane, that is what is used
to define an "other cut". This curve can be seen in any
view.

For B-splines, this refers to the independent
value or parameter that is used to define the curve or surface.
For curves, the parameter is called 'u' and its value changes
from 0.0 at one end of the curve to 1.0 at the other end.
Rectangular-like B-spline surfaces have two parameters: constant
'u' for the row direction and constant 'v' for the column
direction. Their values also range from 0.0 to 1.0, so that every
combination of 'u' and 'v' values between 0.0 and 1.0 define the
entire surface.

This term refers to the area on a B-spline
surface located between consecutive rows and columns of the
surface. Therefore, all of the rows and columns subdivide the
surface into a grid of patches. The program sometimes allows you
to deal with the surface on a patch-by-patch basis.

This term is used to describe the process of
selecting an object on the screen. First you position the cursor
near the object or entity and then you press and release (click)
the left mouse button. Many commands require you to select an
object by "picking" it.

The pixel is the smallest unit of resolution
for an output device. It is usually used to describe the
resolution of the display screen. Although laser printer output
is made up of dots (or pixels), one usually refers to its output
in terms of dpi or "dots per inch".

This term usually refers to a surface of a boat
which can be created out of flat material, like aluminum or
plywood. This means that the surface is developable. This term is
also used to refer to the sheet of steel or aluminum that will be
used to construct the boat, whether or not the surface is
developable.

This is a series of 3D points in space
connected by straight lines. For this program, polyline is
considered to be a variation of the curve entity, which can
define NURB curves, polylines, and combinations of the two.

This term refers to a particular type of
equation that is used as the basis for all B-spline curves and
surfaces. A polynomial has the general form: F(x) = a0 + a1*x +
a2*x^2 + a3*x^3 + ... The highest exponent value that is used (3,
in this example), is called the degree of the polynomial
(degree=3 is also called a cubic polynomial). The number of
coefficients ('a' values) is the order of the polynomial. Order
is always one more than degree.

This defines a geometrical connection between
two entities that is enforced by the program. For example, if you
fix a point to a curve, then you can only move or drag the point
along that curve. Likewise, if you move the curve, the point will
remain attached to the curve and remain in the same relative
position.

In discussing B-splines or NURBS, a row is one
of the iso-parametric curves which define these surfaces.
"Columns" lie in a direction perpendicular to rows.
These surfaces are made up of a rectangular-like mesh of rows and
columns.

These are straight lines which lie entirely on
a surface, traveling from one edge of the surface to another. If
a surface can be constructed entirely of non-overlapping ruling
lines, it is said to be developable and can be constructed out of
flat material. Note that all flat, conical, and cylindrical
surfaces contain ruling lines and are developable.

This is the well-defined curve which forms the
junction between the deck and the hull.

This term refers to a technique whereby a point
is automatically shifted to a near-by grid point. This is useful
if you have to define or move points to positions which fall
exactly on the intersections of a pre-defined grid. See the Set
Grid, Grid ON, and Snap ON commands.

This is the curve defined by intersecting a
transverse cut plane (X-value) through the hull geometry.
Although station specifically defines one of the cross-sections
used to define the boat, it may be used in a more general sense
for any cross-section, and may be used interchangably with the
term "frame". This curve can be seen in the section
view.

The status line is the line at the bottom of
the application window which displays user prompts, warning
messages, and error message. You should always look there if you
are not sure what is happening.

These are structural members which are attached
(welded, perhaps) along the length of the boat. They are
sometimes called longitudinals.

This is the transverse distance from the
centerline to the center of the volume of the underwater portion
of the boat. It is calculated by the Hydro Calc command. This
value is zero for symmetrical boats in the upright condition. It
will not be zero if you specify an heel angle.

This term refers to the process of turning on
and off a switch type of command or option (like a light switch).
The first time you use a command, you turn on the option, and the
next time you select the command, you turn it off.

For B-Splines, this term refers to the constant
or uniform spacing of the defining set of knot values (knot
vector). The knots are part of a B-spline definition and can be
used to control the shape of the curve or surface.

This is the distance from the baseline (Z=0) to
the center of the underwater volume of the boat.

This is the distance from the baseline (Z=0) to
the vertical position of the center of gravity of all of the hull
weights. This value is obtained from a weight study (see the
Weights program) of the boat which identifies all of the weight
items (hull, joinery, machinery, etc.) that make up the boat..
This is a very important number which affects the motions and
stability of the boat.

This is a term used to describe the official
defining points of a B-spline curve or surface. These points do
not necessarily lie on the curve or surface, but they do
influence its shape. For every vertex point, however, there is an
associated point on the curve or surface. Since you can
mathematically convert one point to the other, then sometimes the
points on the surface are referred to as defining points. This
program allows you to control shapes using either point.

This is the curve defined by intersecting a
horizontal plane (Z-value) through the hull geometry. All
waterlines are parallel to the main design waterline or
waterplane. The curve can be seen in the plan view of the boat.

This is a generic term used by many programs to
refer to the process of enlarging (and sometimes reducing) the
view that appears on the screen. This can be done many ways: as a
percentage magnification factor (zoom in), as a scale down factor
(zoom out), or an enlarge defined by a user-specified rectangle
in the view (zoom window).