Engineering Drawing is the systematic graphical representation of objects, machines, components, structures and spatial designs so that their shape, size, position, construction, assembly and operation can be communicated accurately. It is closely related to Technical Drawing, Machine Drawing, Descriptive Geometry and Computer-Aided Design (CAD).
Engineering drawing is fundamentally concerned with transforming information about three-dimensional object space into drawings, projections and models that can be understood, measured, manufactured and constructed. It uses several different perspective and projection systems, particularly Parallel Perspective, Orthographic Projection, Multi-View Projection, Axonometric Projection and Oblique Projection, while linear or central perspective can also be used where a more visually realistic view is required.
Perspective is therefore not incidental to engineering drawing. It provides many of the geometrical principles through which spatial objects can be viewed, projected, measured, modelled and represented.
What Is Engineering Drawing?
Engineering drawing is a form of technical graphical communication used to describe how an object or system is designed, constructed, assembled or manufactured.
A drawing may communicate information about:
- overall shape and form;
- dimensions;
- scale;
- relative position of components;
- internal and external structure;
- assembly relationships;
- manufacturing requirements;
- tolerances;
- materials or components; and
- the way a machine or structure functions.
The aim is not necessarily to imitate the way an object looks naturally to the eye. Instead, the drawing system is selected according to the information that needs to be communicated.
Engineering Drawing and Perspective
The Dictionary of Perspective identifies Technical / Engineering Drawing Perspective as the use of drawing and projection to communicate how something functions or is constructed.
Within engineering drawing, spatial objects can be represented according to different projection principles.
- Parallel Perspective preserves parallel projection directions and is fundamental to engineering and technical drawing.
- Orthographic Projection produces plans, elevations, sections and other measurable views.
- Axonometric Projection shows several dimensions of an object simultaneously within one pictorial view.
- Oblique Projection preserves a principal face while projecting depth obliquely.
- Linear Perspective can represent how the completed object appears from a finite viewpoint.
Engineering drawing therefore uses different kinds of perspective for different functions rather than relying upon one universal projection method.
Why Parallel Perspective Is Fundamental
Parallel Perspective is particularly important to engineering drawing because its projectors remain parallel rather than converging towards a finite centre of projection.
This avoids the ordinary diminution of projected size associated with central or optical perspective. Equal structures positioned at different represented depths do not automatically become progressively smaller simply because they are farther away.
This makes parallel projection especially useful for:
- measurement;
- design;
- manufacturing;
- construction;
- comparison of dimensions;
- component relationships; and
- systematic description of three-dimensional form.
Parallel Perspective therefore prioritises geometrical clarity and controllable scale over the optical appearance generated by a finite viewpoint.
Orthographic Projection
Orthographic Projection is one of the principal foundations of engineering drawing.
It is a form of parallel projection in which the projection lines are perpendicular to the projection plane.
A three-dimensional object can be represented through a coordinated set of two-dimensional views, commonly including:
- front view;
- top or plan view;
- side view;
- bottom or rear views where required;
- auxiliary views; and
- sectional views.
The number of views should be sufficient to define the object unambiguously. Three principal views are common, although simpler objects may require fewer.
Primary and Multi-View Projection
Primary Projection or Multi-View Projection represents a three-dimensional object through several mutually related orthographic views.
A typical set contains:
- Plan — a view from above or below;
- Front Elevation — a view directly towards the front;
- Side Elevation — a view from one side.
These separate views correspond to different directions around the same object.
Together they can provide a far more complete description of three-dimensional geometry than one isolated pictorial view.
The principle can be expressed as:
3D Object → Several Orthogonal Projection Directions → Coordinated 2D Views → Defined 3D Form.
Plans
A Plan is an orthographic view projected from above or, in some applications, from below.
Plans are particularly useful for showing:
- horizontal dimensions;
- positions of components;
- layout;
- alignment;
- relative spacing; and
- relationships between parts.
Because the view is not produced through ordinary finite-viewpoint recession, a plan can provide a stable framework for accurate graphical measurement within the conditions and scale of the projection.
Elevations
An Elevation is an orthographic representation of an object viewed directly from the front, back or side.
A front elevation can show the frontal arrangement and dimensions of a machine, building or component, while a side elevation reveals its corresponding lateral organisation.
A feature parallel to the projection plane can retain its true shape and size at the selected drawing scale. Features inclined to the projection plane may appear foreshortened and may therefore require another view or an auxiliary projection.
Sectional Views
A Sectional View or Sectional Perspective Drawing reveals the internal structure of an object by imagining that the object has been cut by a plane.
The portion in front of the cutting plane is conceptually removed so that otherwise hidden internal features can be shown.
Sectional drawings may include:
- full sections — the complete object is cut through;
- half sections — only half is cut;
- broken-out sections — a local portion is removed to reveal an internal feature.
Sections are particularly important where the construction or operation of an object depends upon spatial relationships that cannot be understood from its external surfaces alone.
First-Angle and Third-Angle Projection
Engineering drawings commonly organise their orthographic views through First-Angle or Third-Angle Projection.
Both systems establish a consistent relationship between the three-dimensional object, the directions from which it is projected and the positions of the resulting views on the drawing.
The Dictionary of Perspective and Volume 1 associate both systems with Primary or Multi-View Projection, Descriptive Geometry and technical or engineering drawing.
The essential purpose is the same: to organise several orthogonally related views so that they can be interpreted together as a consistent representation of one three-dimensional object.
Descriptive Geometry
Descriptive Geometry provides a major geometrical foundation for engineering drawing.
It represents three-dimensional objects in two dimensions through a systematic set of projections and geometrical procedures.
Coordinated orthographic and auxiliary projections can be used to determine:
- true size;
- true shape;
- true length;
- inclination;
- position;
- intersection; and
- spatial relationships between components.
Descriptive Geometry therefore allows complex spatial problems to be translated into graphical constructions that can be inspected and solved on a two-dimensional surface.
Auxiliary Views
Auxiliary Views are used when an inclined line or surface cannot be represented in its true shape or size within the principal front, top or side views.
A new projection direction is selected so that the feature of interest is viewed in a geometrically useful orientation.
This may reveal:
- true length;
- true inclination;
- true shape of an inclined surface; or
- dimensions obscured by foreshortening in a primary view.
Auxiliary projection demonstrates an important principle of engineering perspective: there is no requirement to describe every feature from one fixed viewpoint. Different views can be selected according to the information that needs to be recovered or communicated.
Axonometric Projection
Axonometric Projection provides a pictorial parallel view in which several principal dimensions of a three-dimensional object can be shown simultaneously.
The object is oriented so that its principal axes are projected together within one drawing.
Axonometric projection is divided principally into:
- Isometric Perspective — all three principal axes share the same projected scale or degree of foreshortening;
- Dimetric Perspective — two principal axes share the same scale while the third differs;
- Trimetric Perspective — all three principal axes have different projected scale factors.
These systems allow a three-dimensional object to be represented pictorially while retaining the parallel structure characteristic of Parallel Perspective.
Isometric Drawing
Isometric Projection is one of the most widely used axonometric methods in technical and engineering drawing.
The three principal object axes are equally foreshortened and their projected directions are separated by equal angular relationships of 120 degrees.
The common scale relationship along the three principal axes provides a convenient framework for representing and comparing dimensions.
Isometric drawings are therefore especially useful where a single image needs to communicate the general three-dimensional construction of an object more immediately than separate plans and elevations.
Dimetric and Trimetric Drawing
Dimetric and Trimetric Projection provide alternative axonometric systems.
- In Dimetric Perspective, two principal axes have equal projected scale and the third differs.
- In Trimetric Perspective, all three principal axes possess different projected scales.
These differences allow the orientation and appearance of an engineering object to be adjusted while remaining within an axonometric parallel-projection framework.
Oblique Projection
Oblique Projection is another form of Parallel Perspective used in technical drawing.
Unlike orthographic projection, the projection rays meet the projection plane obliquely rather than at right angles.
A principal face can therefore be shown in a convenient frontal relationship while the depth dimension is projected at an angle.
Important forms include:
- Cavalier Projection;
- Cabinet Projection;
- Military Projection;
- Plan-Oblique Projection; and
- general Oblique Projection.
The projected depth scale can vary according to the method employed, so measurements must always be interpreted according to the particular scale conventions of the drawing.
Cavalier and Cabinet Projection
Cavalier and Cabinet Projection are two familiar forms of oblique engineering drawing.
In Cavalier Projection, receding depth can be represented at full scale, which can make the resulting object appear visually elongated.
Cabinet Projection reduces the represented depth scale, producing a less exaggerated pictorial appearance.
Both preserve the convenience of presenting a principal face directly while displaying depth through oblique parallel lines.
Paraline Drawing
Paraline Drawing is a broad term for pictorial parallel-projection methods such as axonometric and oblique drawing.
Paraline drawings are especially useful when spatial relationships and measurable constructional information are more important than reproducing the visual appearance generated by a finite viewpoint.
Families of corresponding object-space parallels remain parallel within the drawing and therefore do not converge towards finite vanishing points.
This distinguishes a paraline framework from a central-perspective framework in which receding parallel directions generally converge.
Engineering Drawing versus Linear Perspective
Engineering drawing should not be equated exclusively with Parallel Perspective.
Linear or Central Perspective can also be used to explore an engineering or architectural model, particularly where the aim is to communicate how the completed object will appear from a particular viewpoint.
The two approaches answer different questions.
- Parallel / Orthographic Drawing: What is the object’s geometrical form, size and construction?
- Central / Linear Perspective: How will the object appear from a selected finite viewpoint?
An engineering project can therefore use both methods at different stages or for different communicative purposes.
True Shape and True Size
The ability to establish true shape and true size is one of the most important functions of engineering projection.
In an orthogonal projection, a planar feature parallel to the projection plane can be shown in its true shape and at the selected drawing scale.
An oblique or inclined feature is generally foreshortened in that view and therefore does not automatically appear in true shape.
Another primary or auxiliary view can then be constructed in which the feature is appropriately aligned with the projection plane.
This is why an accurate engineering description often depends upon several coordinated views rather than one supposedly perfect view.
Scale in Engineering Drawing
Scale allows very large or very small spatial objects to be represented at manageable drawing dimensions while preserving controlled proportional relationships.
A machine component, building, vehicle or other object can therefore be modelled and represented at a selected scale rather than being drawn at its physical size.
Volume 1 emphasises that perspective and technical drawing enabled different scales and views of an object to be systematically related, thereby contributing to the increasing importance of measurement and quantification in science and engineering.
Scale is therefore not merely a matter of fitting a drawing onto paper. It provides a controlled relationship between object space and drawing space.
Dimensions and Measurement
Engineering drawings are commonly dimensioned so that physical sizes and spatial relationships can be communicated explicitly rather than estimated from visual appearance alone.
Dimensions can specify:
- length;
- width;
- height;
- depth;
- diameters and radii;
- angles;
- positions;
- clearances; and
- relationships between components.
The engineering drawing therefore operates not merely as a picture, but as a measurable and quantitative spatial description.
Machine Drawing
Machine Drawing is a specialised form of technical and engineering drawing concerned with machines and their components.
A machine drawing can communicate both external and internal construction and may include:
- component shape and size;
- relative position;
- machining information;
- tolerances;
- bill of materials;
- assembly relationships; and
- manufacturing information.
Perspective and projection allow individual components to be isolated, represented, measured and then related back to the complete machine.
Part and Assembly Drawings
Engineering and machine drawings can be divided according to the information they communicate.
- Part Drawing — describes one individual component, including its form and dimensions.
- Assembly Drawing — shows how several components fit together to form a larger working object or machine.
- Exploded View — separates components spatially so that their order, alignment and relationships can be understood more clearly.
These forms show that engineering drawing can represent both the individual part and the structural system of which it forms a component.
Exploded Engineering Drawings
An Exploded View separates the parts of an object while retaining their relative orientation and alignment.
The components may be displaced along principal axes, while connecting or alignment lines indicate:
- their original positions;
- the order of assembly;
- directions of movement; and
- relationships between components.
Exploded drawings can be produced in:
- isometric;
- axonometric;
- dimetric;
- trimetric;
- oblique; or
- plan-oblique forms.
This makes the exploded view particularly useful for communicating complex assemblies whose internal relationships would otherwise be hidden.
Engineering Drawing and Manufacturing
Engineering drawing provides the graphical bridge between design and manufacture.
A proposed machine or component can be geometrically developed and represented before it physically exists.
Its dimensions, component relationships and construction can therefore be examined, corrected and communicated before manufacturing begins.
Volume 1 emphasises the historical importance of this capability: accurate technical, engineering and machine drawings allowed increasingly complex objects and machines to be designed with precision and then manufactured according to controlled spatial specifications.
Engineering Drawing and the Industrial Age
The development of systematic technical and engineering drawing became especially important with the growth of industrial design and manufacture.
By the nineteenth century, increasingly specialised branches of graphical perspective included:
- architectural drawing;
- engineering drawing;
- industrial drawing;
- machine drawing;
- mechanical drawing;
- construction drawing;
- technical drawing; and
- map and plan drawing.
These methods increasingly codified spatial representation so that designs could be transmitted accurately between designers, engineers, manufacturers and builders.
Perspective thereby became an enabling technology of modern design and manufacturing rather than remaining principally an artistic method for depicting spatial appearance.
From Hand Drafting to CAD
Modern engineering drawing has increasingly moved from manual drafting to Computer-Aided Design (CAD).
CAD does not eliminate the underlying geometrical and perspective principles. Instead, it implements and extends them computationally.
A digital engineering system can contain a three-dimensional geometrical model from which many different representations can be generated, including:
- plans;
- elevations;
- sections;
- orthographic views;
- axonometric views;
- oblique views;
- exploded views;
- perspective renderings; and
- other calculated or simulated views.
The perspective method is therefore no longer tied to one fixed drawing. The computer model can generate different views according to the purpose of the engineering task.
3D CAD Models
A modern CAD system can create a three-dimensional geometry model rather than only a collection of separate two-dimensional drawings.
Once created, this model can be viewed and projected in many ways.
The process can be represented as:
Engineering Concept → 3D Geometrical Model → Selected Projection / View → Technical Drawing, Measurement or Visualisation.
The same underlying geometry can therefore support multiple engineering perspectives without the object having to be redrawn independently for every view.
Engineering Models and Simulation
Volume 1 describes modern engineering modelling as extending well beyond the production of static drawings.
CAD and related systems can be associated with models and simulations involving:
- moving components;
- kinematics;
- strength;
- materials;
- temperature;
- friction and movement;
- lighting;
- ageing; and
- other physical or mechanical behaviours.
These simulations involve engineering principles beyond perspective itself, but they depend upon a sufficiently accurate geometrical model of how the design is distributed and constructed in physical space.
Perspective and geometrical representation therefore provide part of the spatial framework upon which more complex engineering analysis can operate.
Design before Construction
One of the most important functions of engineering drawing is that an object can be designed before it exists physically.
A proposed structure can be:
- represented;
- measured;
- modified;
- compared;
- assembled virtually;
- tested computationally; and
- communicated to other people.
This separates the process of developing a spatial solution from the expense and difficulty of constructing every possible version physically.
Engineering drawing therefore connects imagined spatial form with future physical reality.
Engineering Drawing as Spatial Communication
An engineering drawing is fundamentally a communication system.
Its purpose is not merely to create an attractive picture but to transmit enough spatial information for another person or system to understand the intended object.
This can include communicating:
- what the object is;
- how large it is;
- how its components are positioned;
- how those components fit together;
- which features are internal or external;
- how the object is manufactured; and
- how the completed system is expected to function.
The choice of projection is therefore governed by the information that the drawing is intended to convey.
Measurement versus Visual Appearance
Engineering drawing demonstrates an important distinction between measurable representation and natural visual appearance.
A conventional photograph or central-perspective drawing represents spatial objects from a finite viewpoint and therefore contains diminution, convergence and other projective transformations.
An orthographic engineering drawing intentionally suppresses many of these optical effects so that dimensions and constructional relationships can be represented more systematically.
This does not make one method more correct than the other. They serve different functions:
- optical or central projection emphasises appearance from a viewpoint;
- orthographic and parallel projection emphasise controlled geometrical description.
Engineering Drawing and 2D Perspective
Much traditional engineering drawing represents three-dimensional spatial objects through two-dimensional drawings.
A plan, elevation or section is a 2D image that contains selected information about a 3D object.
Several such views can be combined to communicate the complete spatial geometry more effectively.
Engineering drawing therefore provides an important example of the general perspective transformation:
3D Object Space → Geometrical Projection → 2D Technical Image Space.
Engineering Drawing and 3D Perspective
Engineering drawing also belongs directly to the larger study of 3D Perspective.
The purpose of the drawing system is frequently to describe, construct or analyse forms situated within three-dimensional object space.
Modern CAD systems go further by maintaining the engineering design itself as a three-dimensional model from which two-dimensional and three-dimensional views can be produced.
The dimensional relationship may therefore be:
- 3D object → 2D engineering drawing;
- 3D object → 3D CAD model;
- 3D CAD model → multiple 2D technical projections; or
- 3D CAD model → pictorial or interactive 3D representation.
Technical Perspective and Engineering Drawing
The term Technical Perspective can be used broadly for systematic methods of viewing, measuring, calculating, constructing, projecting or representing spatial objects and scenes.
Engineering drawing is an important application within this larger technical field.
However, Technical Perspective should not be treated as an additional principal Perspective Category. It is a broad descriptive term that can involve several different categories, methods and systems.
Engineering Drawing and Perspective Category Theory
Within Perspective Category Theory, Engineering Drawing operates principally through several interacting Perspective Categories.
- Mathematical Perspective — geometry, coordinates, projection, scale, measurement and calculation.
- Graphical Perspective — plans, elevations, sections, axonometric, oblique and other drawings.
- New Media Perspective — CAD, digital modelling and computational representation.
- Instrument Perspective — measuring, surveying, imaging or manufacturing systems used in conjunction with engineering representation.
- Visual Perspective — the resulting drawings and models as they are visually inspected and interpreted.
Engineering drawing can therefore be understood as a category chain linking geometrical modelling, graphical representation, digital processing, measurement and visual interpretation.
A modern engineering workflow might therefore be expressed as:
Design Concept → Mathematical / Geometrical Model → CAD Model → Technical Projections and Drawings → Measurement / Simulation → Manufacture or Construction.
Why Engineering Drawing Matters to Perspective
Engineering Drawing reveals that perspective has functions far beyond producing a visual illusion of depth.
Perspective can also be used to:
- measure;
- calculate;
- design;
- model;
- compare;
- specify;
- communicate;
- manufacture;
- assemble; and
- construct spatial objects.
Engineering drawing is therefore one of the clearest examples of perspective operating as a practical spatial technology.
Its development allowed proposed objects to be represented precisely before they existed and enabled highly complex physical systems to be divided into understandable and measurable components.
Engineering Drawing — Frequently Asked Questions
What is Engineering Drawing?
Engineering Drawing is the systematic graphical representation of machines, components, structures and other spatial objects so that their shape, size, construction, dimensions, assembly and operation can be communicated accurately.
Is Engineering Drawing a form of perspective?
Yes. Engineering drawing uses several perspective and projection systems, especially Parallel, Orthographic, Axonometric and Oblique Perspective. Central or Linear Perspective can also be used where a realistic finite-viewpoint image is required.
Why is Parallel Perspective important in Engineering Drawing?
Parallel projection avoids the ordinary diminution produced by finite central projection and provides stable geometrical relationships useful for measurement, comparison, construction and manufacturing.
What is Orthographic Projection?
Orthographic Projection is a parallel-projection method in which the projection direction is perpendicular to the projection plane. It is widely used to create front, top, side and other technical views.
What is Multi-View Projection?
Multi-View Projection describes a three-dimensional object through several coordinated two-dimensional views, commonly including plan, front elevation and side elevation.
What is the difference between a plan and an elevation?
A plan normally represents an object from above or below, while an elevation represents it directly from the front, rear or side.
What is a sectional engineering drawing?
A sectional drawing imagines a cut through the object so that normally hidden internal structures can be represented and understood.
What is an Auxiliary View?
An Auxiliary View is an additional projection used to reveal the true length, inclination, size or shape of a feature that appears foreshortened in the principal orthographic views.
What is Axonometric Drawing?
Axonometric Drawing is a pictorial parallel-projection method that represents several principal dimensions of a three-dimensional object within one image. Its principal forms are isometric, dimetric and trimetric projection.
What is Isometric Drawing?
Isometric Drawing is an axonometric system in which the three principal axes have equal projected scale or foreshortening. It is widely used in engineering and technical representation.
What is Oblique Projection?
Oblique Projection is a parallel-projection system in which the projectors meet the projection plane obliquely rather than perpendicularly. Cavalier and Cabinet Projection are two familiar forms.
What is an Exploded View?
An Exploded View spatially separates the components of an assembly while retaining their orientation and alignment so that their relationships and order of assembly can be understood.
Can dimensions be measured directly from an Engineering Drawing?
Engineering drawings use controlled scales and explicit dimensions, but measurement depends upon the projection used. Features parallel to an orthographic projection plane can retain true shape and size at the selected scale, while inclined features may be foreshortened and require another or auxiliary view.
What is Descriptive Geometry?
Descriptive Geometry is the systematic geometrical representation of three-dimensional objects in two dimensions using coordinated projections. It provides important foundations for technical, architectural and engineering drawing.
What is CAD?
Computer-Aided Design uses digital geometry and computer modelling to create, modify, analyse and represent engineering designs. Modern CAD systems can produce many plans, elevations, sections, pictorial views and simulations from a common geometrical model.
Did CAD replace perspective?
No. CAD automates and extends many of the geometrical, projection and modelling principles historically used in engineering drawing. The underlying problems of viewpoint, projection, dimension, scale, shape and spatial representation remain.
Is Engineering Drawing the same as Technical Drawing?
The terms overlap strongly. Technical Drawing is the broader discipline of drawings used to communicate how objects function or are constructed, while Engineering Drawing is particularly associated with engineering design, manufacture, machines, components and related spatial systems.
Is Technical Perspective a separate Perspective Category?
No. Within Perspective Category Theory, Technical Perspective is a broad descriptive term for systematic methods of viewing, measuring, calculating, constructing and representing spatial reality rather than an additional principal Perspective Category.
Why is Engineering Drawing important?
Engineering Drawing enables spatial objects and systems to be designed, measured, communicated and tested before construction or manufacture. It has therefore been fundamental to the development of modern engineering, industrial production and Computer-Aided Design.
Engineering Drawing within the Wider Field of Perspective
Engineering Drawing demonstrates one of the most important expansions in the history of perspective: the movement from perspective as a means of depicting spatial appearance towards perspective as a means of designing, measuring and constructing spatial reality.
Plans, elevations, sections and multi-view projections allow a three-dimensional object to be analysed through coordinated two-dimensional representations. Axonometric and oblique drawings provide pictorial but measurable descriptions of form. Linear perspective can show how the proposed design will appear from a finite viewpoint. Modern CAD can unite these operations within one digital three-dimensional model.
The engineering drawing is therefore not merely an illustration of an object. It can operate as a precise spatial model, specification, measurement system, manufacturing instruction and design tool.
Seen in this wider context, Engineering Drawing demonstrates the practical power of perspective to connect geometry, representation, measurement, modelling, design and physical construction.