La Rioja PAU Technical Drawing Applied to Plastic Arts and Design II flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Thales' theorem

An angle inscribed in a semicircle is a right angle. Used to construct perpendiculars and right triangles with compass and straightedge from a given diameter.

Perpendicular bisector locus

The set of points equidistant from the endpoints of a segment. It is perpendicular to the segment at its midpoint, and the three bisectors of a triangle meet at the circumcentre.

Regular polygon exterior angle

For a regular polygon with n sides the exterior angle is 360°/n and the interior angle is 180° − 360°/n. These values set the compass opening for stepwise construction.

Golden ratio value

φ = (1+√5)/2 ≈ 1.618. A rectangle with sides in this ratio, when a square is removed, leaves a smaller rectangle of the same proportion.

Tangent from external point

Draw the circle with diameter equal to the segment joining the external point to the centre. Its intersections with the given circle are the two tangency points.

Similarity ratios

If two similar figures have linear ratio k, their areas are in ratio k² and their volumes in ratio k³. A 1:2 model has one quarter the surface and one eighth the volume.

Scale factor definition

Scale = drawing length divided by real length. At 1:50, one centimetre on the drawing represents 50 cm, that is 0.5 m, in reality.

Fourth proportional

The value x satisfying a/b = c/x, so x = bc/a. Constructed graphically by Thales' intercept theorem using two rays from a common vertex.

ISO 216 A-series

Paper sizes with aspect ratio √2:1. A0 has an area of one square metre and each following size halves the area, so A4 is one sixteenth of a square metre.

Dividing segment into n parts

Draw an auxiliary ray from one endpoint, step off n equal lengths, join the last point to the other endpoint, then draw parallels through the marks.

True length by change of plane

Introduce a new projection plane parallel to the segment. The segment then projects at true length, and a second change gives true shape of a face.

Dihedral angle measurement

The angle between two planes is measured in a plane perpendicular to their line of intersection. In that section the angle appears in true size.

Point-to-plane distance

The length of the perpendicular from the point to the plane. In multiview it is found after obtaining the plane as an edge view.

Surface development method

Unroll a developable surface such as a cylinder or cone into a plane. The shortest path between two points on the surface becomes a straight line in the development.

Rotation method

Rotate the object about an axis perpendicular to a projection plane until the element is parallel to that plane, keeping one coordinate constant to reveal true length.

First-angle projection

European convention in which the object sits between observer and plane. The top view is placed below the front view and the left view to the right.

Third-angle projection

American convention in which the projection plane lies between observer and object. The top view appears above the front view and the right view to the right.

Line types in technical drawing

Continuous thick lines for visible outlines, dashed lines for hidden edges, long-short dashes for centre lines, and thin continuous lines for dimension and extension lines.

Dimensioning placement rule

Each dimension is given once, on the view where the feature appears in true shape. Dimension lines run parallel to the measured edge, outside the outline, with values above the line.

Datum dimensioning

All dimensions are measured from one common reference origin rather than chained end to end. This avoids accumulation of tolerance errors across a part.

Auxiliary view purpose

A view projected perpendicular to an inclined face so that face appears in true size and shape. Depths are transferred from the adjacent principal view.

Isometric foreshortening factor

True isometric projection shortens each axis by about 0.816. Isometric drawing uses full scale along the axes, which enlarges the image by roughly 22 percent.

Cabinet oblique projection

The front face is drawn true shape and parallel to the picture plane; receding edges are drawn at 45° at half scale to reduce apparent distortion.

Vanishing point definition

The intersection of the picture plane with the line through the station point parallel to a family of parallel lines. All lines of that family converge there.

Cone of vision limit

The picture should subtend roughly 30° to 60° at the eye, never more than 60°, otherwise perspective distortion appears at the edges of the image.

Measuring points in perspective

Points on the horizon used to transfer true lengths onto receding lines. Each principal direction has its own measuring point derived from the station point.

Two-point perspective

Both sets of horizontal edges recede to two vanishing points on the horizon, used when a corner of the object faces the viewer rather than a flat face.

Additive and subtractive colour

RGB light mixes additively toward white; CMY pigment mixes subtractively toward black. The two systems use complementary primaries and different mixing rules.

Complementary colour contrast

Colours opposite on the colour wheel produce maximum chromatic contrast. Adjacent analogous colours instead give harmony and lower visual tension.

Simultaneous contrast

A colour appears shifted toward the complement of its surrounding field, so identical swatches look different against different backgrounds.

Gestalt grouping laws

Proximity, similarity, continuity, closure and figure-ground describe how separate marks are perceived as organised forms rather than isolated elements.

Rule of thirds

Dividing the frame into a three-by-three grid and placing key elements near the intersections yields dynamic balance compared with central, symmetrical placement.