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Projective Geometry

1639 CE17th-century France (Desargues)

Through Projective Geometry: What survives when shapes change, and which rules divide one world from another?

Begin with lengths and angles, then move toward less visible properties of space: connection, holes, and dimension.

This voyage is an editorial path for understanding, not a claim of direct historical influence or sole invention.

Understand it in one breath

"What if parallel lines meet at a point at infinity?" The idea grew from Renaissance perspective and was formalized by Desargues in the 17th century. An ideal pinhole camera projects 3D points onto an image plane; real lenses also introduce distortions that must be modeled separately. Projective geometry is basic to computer vision, 3D graphics, and camera calibration.

At a glance

HorizonPoint at infinity [0 : 1 : 0]Two parallel rails meet at a point at infinityIn ℙ², every family of parallel lines meets at exactly one point

Concept

Geometry with "points at infinity" — discovered for Renaissance perspective, foundational for algebraic geometry.

Key formula

[x:y:z][λx:λy:λz],λ0[x : y : z] \sim [\lambda x : \lambda y : \lambda z],\quad \lambda \neq 0

Ports in time

This concept was not invented in one instant

Follow the scenes to see problems, notation, standards of proof, and applications changing across different times and places.

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AD 1413Scene 1 / 4Florence

Brunelleschi — mathematical perspective

In Florence, architect Filippo Brunelleschi used a view of the Baptistery to demonstrate linear perspective, helping open a new chapter in Renaissance art.

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AD 1639Scene 2 / 4Lyon

Desargues — an early treatise on projective geometry

Girard Desargues published a unified geometry using points at infinity. Its unfamiliar language left the work largely overlooked for generations.

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AD 1822Scene 3 / 4Continue through the world of this year

Poncelet — a revival

Ideas Jean-Victor Poncelet developed while a prisoner of war helped revive projective geometry and drive the 19th-century renewal of geometry.

No reliable place is given, so time continues without an invented pin

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AD 1980Scene 4 / 4Continue through the world of this year

Homogeneous coordinates in computer graphics

Three-dimensional graphics adopted four-component homogeneous coordinates so translation, rotation, projection, and perspective could be combined with matrix operations.

No reliable place is given, so time continues without an invented pin

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Modern applications

Homogeneous coordinates in computer graphics, camera calibration, projection in 3D games, machine vision, and algebraic geometry.

Beyond MathVoyage

Curated sources and problems. Bring one discovery back from OEIS, Project Euler, MathOverflow, or arXiv.

No concept belongs to one person

Follow people who played different roles

These are not inventor credits. They are different ports: opening a problem, sharpening a language, or carrying it into another world.

Number lenses

A concept looks different when its world of numbers changes

These numbers are editorial lenses for the voyage, not required prerequisites.

Concept genealogy

What supports it, and what does it open?

Concepts arriving from before

Current port

Projective Geometry

Concepts opened from here

Only direct editorial links are shown; this is not a complete learning order or historical influence line.