LC DCG key terms

A method of representing a three-dimensional object by projecting its features onto two or more mutually perpendicular planes, giving separate views such as plan and elevation that together describe the whole form.

The view of an object seen from directly above, projected onto a horizontal plane. It shows length and breadth, and is normally positioned below or above the front elevation in a standard layout.

A view of an object projected onto a vertical plane, showing height together with either length or breadth. Front, end and side elevations are distinguished by the direction from which the object is viewed.

A view projected onto a plane that is inclined to one or more principal planes, used to show the true shape and size of a slanted face that would appear foreshortened in the standard views.

The actual size and outline of a face or section as it exists on the object, obtained when the projection plane is parallel to that face rather than tilted to it.

A flat surface that is tilted relative to the principal reference planes, so it appears foreshortened in at least one standard orthographic view and requires an auxiliary view to reveal its true shape.

A flat surface inclined to two or more principal planes, so that it is foreshortened in every standard view and cannot be shown at true shape by a single auxiliary projection.

The line of intersection between two projection planes, drawn on a sheet to separate adjacent views and to act as the reference from which heights and distances in each view are measured.

A construction line representing where one projection plane hinges relative to another. Distances are transferred perpendicular to it to build auxiliary views and to relate features between views.

An imaginary flat surface onto which the points and edges of an object are projected to form a view, conventionally arranged as horizontal, vertical and profile planes in a standard layout.

A layout convention in which the object sits between the observer and the projection plane, so the view seen from the front is placed behind the object, and the plan appears below the front elevation.

A layout convention in which the projection plane lies between the observer and the object, so the plan appears above the front elevation and the view from the left is placed on the left.

A dimensioned technical drawing made up of related flat views produced by orthographic projection, used to specify an object precisely for manufacture rather than to suggest its appearance.

The fixed ratio between a length on a drawing and the corresponding real length of the object, stated as a ratio or representative fraction such as 1:20 or 1:1.

The system of adding sizes, notes and arrowed lines to a drawing so that every feature can be made without scaling off the sheet, following conventions for placement and units.

The conventional range of lines used on technical drawings, including continuous outlines, hidden dashes, centre lines, construction lines and cutting-plane lines, each carrying a distinct meaning.

Features that lie behind visible surfaces in a given view, drawn using evenly spaced short dashes so the reader knows they exist without confusing them with edges that can be seen directly.

A chain-dashed line marking an axis of symmetry, the centre of a circle or the path of a cylindrical feature, used as a construction reference and to locate holes and radii.

A view produced by imagining the object cut by a plane and removing the nearer part, with the cut surface hatched, so internal features appear as solid outlines instead of hidden lines.

An imaginary plane that slices through an object to define where a section is taken, indicated on another view by a chain line with arrows showing the direction of viewing.

A pictorial drawing method in which the three principal axes are drawn 120 degrees apart with equal foreshortening, giving a single three-dimensional view in which all three axes use the same scale.

A reduced scale, about 0.816 of full size, applied along the isometric axes when constructing a true isometric projection, since the axes are foreshortened relative to the real edges.

Any pictorial projection in which an object is rotated relative to the viewing direction so that several faces are visible at once; isometric, dimetric and trimetric forms differ in how much each axis is foreshortened.

A pictorial method in which the front face is drawn true shape and parallel to the picture plane, while receding edges are drawn at an angle, usually half scale, to suggest depth.

A pictorial representation in which parallel receding lines converge towards vanishing points, so objects appear smaller with distance in the way the eye actually perceives them.

The point on the horizon at which a set of parallel receding lines appears to meet in a perspective drawing; each distinct direction of parallel lines has its own vanishing point.

The horizontal line in a perspective drawing representing the eye level of the viewer, on which all vanishing points for horizontal receding lines are located.

A perspective construction in which the object is viewed with a vertical corner nearest the eye, so two sets of horizontal edges recede to two separate vanishing points on the horizon.

A CAD approach in which geometry is driven by named dimensions, constraints and relationships, so that editing a parameter automatically updates all dependent features of the model.

A rule applied in a CAD sketch or assembly that restricts geometry, for example making lines parallel, equal or tangent, or fixing a point in position relative to the origin.

A CAD sketch in which every degree of freedom has been removed by dimensions and geometric constraints, so no element can be dragged to a new position or size.

A CAD technique in which a solid is built as an ordered history of operations such as extrude, revolve, hole and fillet, each stored so it can be edited or suppressed later.

A solid modelling command that combines two bodies by union, subtraction or intersection, for example adding a boss to a part or cutting a cavity out of it.

A CAD representation that encloses a closed volume with surfaces, so it has mass properties and can be sectioned, rendered or prepared for manufacture without ambiguity.

A CAD representation made of connected faces with no enclosed volume, useful for complex outer forms but unable to report mass or guarantee a watertight interior.

A CAD representation consisting only of edges and vertices with no surfaces, giving a quick outline that cannot hide rear edges or support shading and volume calculations.

The process of generating a shaded or photorealistic image from a CAD model by applying materials, lighting and a viewpoint, used to communicate appearance rather than precise dimensions.

A short written statement of the problem to be solved, setting out the user, the need, the constraints and the criteria against which a proposed solution will later be judged.

A detailed list of measurable requirements a product must meet, covering size, materials, performance, cost and safety, written so that a design can be tested objectively against it.

The staged sequence of investigating, defining, generating ideas, developing, testing and evaluating that moves a designer from an identified need to a justified final solution.

The stage in which a finished or prototype solution is judged against the specification and user needs, recording strengths, weaknesses and recommended improvements with evidence.

The study of how people interact physically with products and spaces, applied so that sizes, forces and reaches suit the intended user and reduce strain or injury.

The collection and use of body measurements, such as reach, stature and hand size, to set dimensions so that a product fits the range of users it is designed for.

A straight line that touches a curve at exactly one point without crossing it, meeting a circle at right angles to the radius drawn to that point of contact.

Drawing a line or arc that touches a given circle or curve smoothly at a single point, commonly used to blend curves and lines into continuous outlines in technical graphics.

Joining two lines or curves with a smooth intermediate arc that is tangent to both, so the transition has no visible corner or sudden change of direction.

The set of relationships involving chords, radii, tangents and arcs, including the facts that a tangent is perpendicular to a radius and that the angle in a semicircle is a right angle.

A straight line joining two points on a circle's circumference, which is bisected by the perpendicular drawn from the centre and which subtends an angle at the circumference.

A closed curve traced by a point whose distances from two fixed foci add to a constant total, drawn in graphics using the concentric-circle, trammel or intersecting-lines methods.

The path traced by a point that moves while obeying a stated geometric rule, for example the locus of a point at a fixed distance from a line or from another point.

A three-dimensional curve formed by a point moving around a cylinder while advancing steadily along its axis; its development is a straight line on the unwrapped cylinder surface.

The true-shape flat pattern of a three-dimensional surface, obtained by unfolding it onto a plane, as used for sheet-metal work such as ducts, cones and cylinders.

A development method for surfaces that cannot be unfolded directly, in which the surface is divided into a series of adjacent triangles whose true shapes are found and laid out in order.

The proportion of about 1:1.618 in which a whole relates to its larger part as the larger part relates to the smaller, often used to analyse pleasing proportions in design and graphics.

The relationship between the sizes of parts of a design or composition, judged as a ratio so that elements relate harmoniously rather than by accident.

The arrangement of views, notes, title block and dimensions on a drawing sheet, planned so the drawing is balanced, legible and easy to read in a logical order.

A ruled panel, usually at the bottom right of a drawing sheet, recording the part name, drawing number, scale, projection convention, date, author and revision status.

Rapid drawing by hand without instruments, using light construction lines and consistent proportions to record and communicate ideas before formal drafting begins.

A hand-drawn set of related flat views produced quickly to convey a design idea, keeping correct alignment and proportion even though lines are not drawn with instruments.