Common terms used to describe dimensions of objects/shapes used in technical & engineering drawings
The word “dimension” can be defined as the magnitude of a shape or object in a particular direction; it can also be defined as the linear measurement of a line used to describe the value of the length, breadth, height, thickness, or circumference of an object or structure. A dimension is one of the three coordinates of the position of a point, line, area or volume relative to three imaginary but real axes: x, y, and z.
The most common terms used to describe or express dimensions are height (or depth), length, breadth (or width); all three are often interchanged, with one dimension often being referred to by another name. The most important thing to take note of is the obvious fact each dimension or description refers to the orientation of an object along a particular axis; especially the x, y, and z axes, respectively.
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Many geometric shapes have two dimensions, while other types have three dimensions: width, depth, and height; or length, width, and height—whichever combination. The choice of terms used to describe the dimensions of an object depends on the orientation of the shape and size of the object.
Figure 1: A 3D object (cube) expressed in terms of height, length and depth. (Image credit: Curiositi.)
Figure 2: 2D and 3D rectangular objects expressed in terms of a combination of any 2 and 3 terms: length, breadth and height. (Image credit: Siyavula.)
There are quite a number of geometrical shapes used in technical and engineering drawing; they include: cones, cubes, cylinders, prisms, pyramids, spheres, toroids (doughnut-shaped objects), trapeziums, etc.
Whenever any two different shapes intersect/are used together, a kind of curve, interpenetration or intersection is employed to make sure they fit together. It is very important that students or practitioners be able to draw curves and intersections in order to make good drawings and communicate clearly using the different types of technical drawing.
Figure 3: Types or shapes of objects in 2D. (Image credit: Toppr.)
Figure 4: Types or shapes of objects in 3D. (Image credit: Toppr.)
Usually, a spherical-shaped object like a basketball is usually described as having a radius or diameter, which generally, is just one descriptive term—with the height of a basketball having the same dimension as the diameter.
Figure 5: Other types or shapes of objects in 3D. (Image credit: http://www.mathcaptain.com.)
Usually, a cylindrical shape such as a baseball bat can be described by using terms such as “diameter”, and “length” or “height”—depending on whether it is standing up erect, or lying down flat. A hockey puck would be described using diameter, and width or thickness—i.e., two terms. On the other hand, objects that are not spherical or cylindrical could require three terms to appropriately describe their overall shape—as you might have noticed in Figure 1 (the first figure in this article).
The terms that would be used to describe a car, for instance, would include length, width, and height. Typically, width, height, and breadth would be used to describe a cupboard; while length, width, and thickness could be used to describe a sheet of drawing paper.
Generally, the terms used to describe the dimensions, sizes and shapes of objects are interchangeable, and usually done with respect to the position or orientation of objects when they are being viewed from a particular axis. For example, if a rectangular block is being viewed while it is lying flat on the ground (say, in 2D), it could be described as having a width and height; but if it is placed in a vertical standing position (say, in 3D), and viewed from the side, it could be described as having a height, width and breadth.
In order to avoid confusion, it is advisable that distances observed or taken from left to right be referred to as “width”; distances taken from front to back be referred to as “breadth”; while vertical distances taken from bottom to top (or vice versa) be referred to as “height”. Sometimes, the longest dimension of an object is referred to as the “length”.
In some other instances, there are certain unpopular shapes that are defined by applying mathematical methods; they include the type of complex shapes used in the design of structures such as automobiles, aircraft, and the hulls of ships—amongst many others.