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Joan Lasenby on Applications of Geometric Algebra in Engineering

From Y Combinator · Published Jul 22, 2019 · Watch on YouTube

TL;DR

Geometric algebra (GA) unifies scalars, vectors, bivectors, and trivectors into a single algebraic system that simplifies rotations (via rotors), coordinate-free expressions, and differentiation of geometric objects. It was historically developed by Grassmann, Clifford, and David Hestenes, and includes conformal GA (5D) where points, lines, circles, and spheres are first-class objects.

Key insights

  • Lines are harder than points in classical computer vision; GA makes line-based reconstruction natural because lines are objects in the algebra.
  • Cross product (a × b) works only in 3D; GA’s outer product (wedge) generalizes to any dimension via bivectors, trivectors, etc.
  • Quaternions (i, j, k) are actually unit bivectors (oriented planes) in 3D, not imaginary numbers; GA explains them as rotors.

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