The history of the technical drawing: from sketch to CAD

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§Antiquity and Middle Ages: drawing as a secret art

Already in ancient Egypt and Mesopotamia, carved ground plans of buildings are found on stone and clay tablets. The Romans worked with measurement and building plans, and the architect Vitruvius described in antiquity how a building could be shown in ground plan, elevation, and perspective. In the Middle Ages, building art was often a secret knowledge that the stonemasonry guilds guarded. People liked to draw building parts at full size directly on floors or plastered surfaces – so-called scratch floors – so the stonemason could lay the stone on top of the drawing and carve along the outline.

In the Renaissance, artists and engineers like Leonardo da Vinci began to combine artistic drawing with technical machine sketches. But there was not yet a common, mathematically correct system for showing an object from multiple sides so it could be reproduced precisely. Drawings were personal — two drafters could draw the same thing in two ways.

§Monge and descriptive geometry

The decisive breakthrough came with the French mathematician Gaspard Monge in the late 1700s. As a young draftsman at a military engineering school he developed a method to describe a three-dimensional object with two perpendicular projection planes — what we today know as rectangular projection. His work Géométrie descriptive (descriptive geometry) from 1799 is considered the foundation for modern technical drawing.

With descriptive geometry the trade finally got a common objective language: anyone could now draw the same object in the same way and be understood. It is this system of plan section and elevation that is still the backbone of technical drawing.

§Industrialisation: the drawing office and the common standard language

With industrialisation in the 1800s the need for precise drawings exploded. Machines and parts had to be made identically in factories far from the designer and parts had to be interchangeable. This required that a drawing meant precisely the same thing regardless of who read it. Therefore the drawing office became a workplace and an entire profession of draftspeople arose translating the engineer's ideas into working drawings.

The tools themselves were a craft: drawing board, T-square, drawing triangles, compass, caliper and later the drawing machine with parallelogram arms. You drew with ink on parchment or tracing paper, and copies were produced as dyeline prints (blueprints), where the white lines stood on a blue background. An error often meant that the entire drawing had to be redrawn from scratch.

In the course of the 1900s, the need to standardise drawing language grew so companies and countries could exchange drawings. National standards emerged, and later international ISO standards, for line types, dimensioning, projection method, tolerances and formats. The A series of paper formats we use today and the symbols in the drawing header come from this standardisation wave.

§The digital revolution: from Sketchpad to CAD

The next major shift was the computer. In 1963 Ivan Sutherland demonstrated at MIT the program Sketchpad where with a light pen you could draw directly on a screen and even tie lines together with constraints — a forerunner of today's parametric drawing. Sketchpad was never sold commercially but it showed the way. Through the 1960s and 70s the car and aircraft industries developed expensive large CAD systems on mainframe computers.

The broad breakthrough came when CAD moved from expensive specialist machines to the personal computer. With the launch of AutoCAD in the early 1980s, computer-supported drawing suddenly became something an ordinary drawing office could afford. The drawing board began to disappear and the draughtsman became someone working at a screen.

§The craft today: from drawing to model.

Today the technical designer is rarely one who draws lines with ink. Work happens in parametric 3D models where the 2D drawing is a derived result rather than the starting point. In construction building information models (BIM) combine geometry and data in one model which several trades work in simultaneously. But although the tool has changed from compass to parameter the core task is the same as in Monge's time: to show reality so unambiguously that whoever builds or manufactures can trust the drawing completely.

“The tool has moved from ink and drawing board to screen and parameter — but the task is still to make the room unambiguous on a surface.”

— About the history of technical drawing