PAU Technical Drawing Applied to Plastic Arts and Design II key terms

The line or ray that divides an angle into two equal halves; every point on it lies at the same distance from both sides of the angle. It is the locus used to inscribe circles tangent to two lines.

The line made of all points equidistant from two given points, crossing the segment joining them at a right angle through its midpoint. It locates circumcentres and mirrors of points.

The proportion in which a segment is divided so that the whole relates to the longer part as the longer part relates to the shorter, a value of about 1.618. It is used to analyse harmonic composition.

Any angle whose vertex lies on a circle and whose sides pass through the ends of a diameter is a right angle. It is the standard construction for drawing tangents and right triangles.

The arc of a circle from which a given segment is seen under a constant angle. It is the locus of points forming a triangle with a fixed base and fixed apex angle.

The set of all points that satisfy a stated geometric condition, such as a fixed distance from a point or a line. Constructions are usually solved by intersecting two loci.

A line touching a circle at exactly one point, perpendicular to the radius drawn to that point. Tangency constructions connect arcs and straight lines smoothly in design drawings.

The circle drawn inside a polygon so that it touches every side; its centre is the intersection of the angle bisectors. In design it defines the inner clearance of a shape.

The circle passing through all the vertices of a polygon, centred where the perpendicular bisectors of the sides meet. It gives the outer envelope of a regular figure.

A procedure that divides a circle into equal parts to place the vertices of a polygon with equal sides and angles. Approximate methods exist for polygons such as the heptagon.

An operation that moves or resizes a figure while preserving stated properties, such as translation, rotation, reflection, homothety or inversion. It underpins pattern and modular design.

A scaling transformation about a fixed centre, where every point moves along a ray from the centre and all distances change by the same factor. It produces similar figures of different size.

A curve obtained by cutting a cone with a plane: ellipse, parabola or hyperbola. In technical drawing, conics are constructed point by point and appear in arches and lenses.

A closed convex curve built from four circular arcs with two axes of symmetry, often used as an approximation of an ellipse. Its construction is a classic compass exercise.

A parallel projection in which projectors strike the picture plane at right angles, so lengths parallel to that plane keep their true size. It is the basis of multiview technical drawing.

The standard orthographic views of an object, usually front, top and side, each taken along a principal axis. Together they describe the object's shape without ambiguity.

A multiview arrangement in which the object sits between the observer and the projection plane, so the view is placed on the opposite side. Common in Europe, it follows ISO conventions.

A multiview arrangement in which the projection plane lies between the observer and the object, so each view appears on the same side as the observer. It is standard in the United States.

The flat surface on which the projected image of an object is captured. In dihedral and trihedral systems, mutually perpendicular planes produce the standard sets of views.

The method that projects an object onto two perpendicular planes, horizontal and vertical, then unfolds them into one sheet. It organises plan and elevation into a single drawing.

The line where the horizontal and vertical projection planes meet, shown as the fold line in a dihedral drawing. Heights and depths are measured from it.

A view projected onto a plane that is not one of the principal planes, used to show a slanted face at true shape. It is obtained by projecting perpendicular to that face.

The actual size and form of a face or section when it is parallel to the projection plane. Finding true shape is the goal of auxiliary views and of surface development.

An axonometric projection in which the three axes are equally inclined to the picture plane and separated by 120 degrees, so lengths along them foreshorten equally. Circles appear as ellipses.

A parallel projection of an object tilted to the picture plane so that several faces are visible at once, preserving parallel lines. Isometric, dimetric and trimetric variants differ by axis angles.

An oblique projection in which the front face is drawn true size and receding edges are drawn at half scale, usually at 45 degrees. It is a quick way to sketch depth.

In central perspective, the point where parallel lines receding from the viewer appear to converge on the horizon. Each direction of space has its own vanishing point.

The line in a perspective drawing marking the height of the viewer's eye, on which vanishing points for horizontal lines lie. It fixes the apparent level of the scene.

The position of the observer's eye in a perspective construction, seen as a point in plan. Its distance from the picture plane sets the scale and distortion of the image.

The cone of rays reaching the eye from the scene, whose opening angle limits how much can be drawn without distortion. Keeping within roughly 60 degrees avoids extreme perspective.

A thin line, usually with arrowheads at both ends, that carries a measurement between two extension lines. It shows the value and direction of a dimension.

A thin line drawn from the feature being measured to the dimension line, showing where the measurement begins and ends. It normally stops short of the object outline.

The permitted variation in a dimension, stated as limits or as a plus/minus value, within which the part is still acceptable. It links drawing intent to manufacture.

A symbolic specification controlling form, orientation, location or runout of a feature, given in a rectangular frame. It states the allowed deviation from an ideal geometry.

A theoretically exact reference surface, axis or point from which dimensions and geometric tolerances are measured. Datum symbols in a frame identify these references on the drawing.

The ratio between a drawn length and the real length it represents, such as 1:2 for reduction or 2:1 for enlargement. It must be stated on the drawing sheet.

A view showing the interior of an object as if cut by a plane, with the cut surface hatched. It clarifies hidden features that would otherwise need dashed lines.

Parallel thin lines filling a cut surface in a section view, angled consistently and spaced evenly. Different hatch patterns can distinguish adjacent parts.

The organised arrangement of views, title block, dimensions, notes and frame on a standard sheet format. Good layout follows ISO paper sizes and leaves clear margins.

The relation between the sizes of parts of a composition or figure, often expressed as a ratio. It governs visual balance and can be analysed with regulating lines.

A straight line drawn over an artwork or design to reveal alignments and proportional relationships between elements. It is an analytical tool, not part of the finished work.

A line about which a figure maps onto itself under reflection. Identifying axes helps describe balance, pattern and the structure of a composition.

A network of evenly spaced lines that organises elements into consistent units across a layout. It supports repetition, alignment and scalable design systems.

The flat pattern obtained by unfolding the surfaces of a three-dimensional object onto a plane. It is used to cut and fold sheet materials such as card or metal.

A three-dimensional representation built to a fixed ratio of the real object, used to test form and proportion. It translates drawing conventions into physical space.

A thin line used to locate features, align views or carry measurements in a drawing. It is not part of the object outline but guides construction and dimensioning.