---
tag: 4YDJDTV6B7
kind: concept
name: Descriptive geometry
msc: [51N05]
sources:
  - url: https://en.wikipedia.org/wiki/Descriptive_geometry
same_as:
  wikidata: Q638755
  wikipedia: Descriptive geometry
---

## Summary

Descriptive geometry represents three-dimensional objects by two-dimensional drawings, usually several orthogonal projections, and solves spatial problems by constructions on these drawings.
Its classical form is due to Gaspard Monge.
There a point of space is given by its projections onto a horizontal and a vertical plane, drawn together on one sheet.
From such drawings one can construct true lengths, true angles, intersections of surfaces and shadows.
It was the theoretical basis of technical drawing in engineering and architecture.

## Explanations

### L1 human

An engineer's drawing of a machine part usually shows a top view and a front view, side by side, carefully lined up.
Each view alone loses one dimension, but together they fix the object completely.
Descriptive geometry is the set of rules for making such views and for reading answers from them.
Examples are the true length of a slanted rod or the line where two pipes meet.
It does by careful drawing what analytic geometry does with coordinates.