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Core mathematical underpinnings
2.1. Assumed Maths Core mathematical underpinnings
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Assumed Maths: Coordinate Systems
Assumed mathematical knowledge dealing with coordinate systems
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See links at end for reference material if needed
Coordinate systems The location of a point in space can be described in terms of a coordinate system, defined using an origin reference point and a number of coordinate axes. A coordinate system may be given relative to a parent coordinate system. The Cartesian (rectangular) coordinate system defines coordinate axes which are perpendicular to each other. A given set of coordinate axes spanning a space is called the frame of reference, or basis, for the space. There are infinitely many frames of reference for a given coordinate space.
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Assumed Maths: Vectors
Assumed mathematical knowledge dealing with vectors
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Vectors The following vector concepts should be familiar:
Assume u, v and w are vectors and r and s are scalars For addition and subtraction: u + v = v + u (u + v) + w = u + (v + w) u − v = u + (−v) −(−v) = v v + (−v) = 0 v + 0 = 0 + v = v For scalar multiplication: r(s v) = (rs) v (r + s) v = r v + s v s(u + v) = s u + s v 1 v = v The following vector concepts should be familiar: Vector structure (mostly restricted to 2, 3 or 4 components). Vector addition, subtraction, scalar multiplication and length (including normalisation) Common vector algebraic identities
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Vectors Dot (scalar) product and common ● algebraic identities
Assume u, and v are vectors and r and s are scalars u · v = u1v1 + u2v2 +· · ·+unvn u · v = |u|| v| cos θ u · u = |u|2 u · v = v · u u · (v ± w) = u · v ± u · w r u · s v = rs(u · v) Dot (scalar) product and common ● algebraic identities
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Vectors Assume u, v , w and x are vectors and r and s are scalars u × v = −(v × u) u × u = 0 u · (v × w) = (u × v) · w u × (v ± w) = u × v ± u × w (u ± v) × w = u × w ± v × w |u × v| = |u|| v| sin θ (u × v) · (w × x) = (u · w)(v · x) − (v · w)(u · x) (Lagrange’s identity) r u × s v = rs(u × v) Cross (vector) product and × algebraic identities and dependency upon coordinate system ‘handedness’. A right-handed system is assumed.
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Vectors Understanding that the scalar triple product, i.e. (u × v) · w or [uvw] geometrically corresponds to the signed volume of the parallelepiped formed by vectors u, v and w.
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Assumed Maths: Matrices
Assumed mathematical knowledge dealing with matrices
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Matrices The following matrix concepts should be familiar:
Matrix structure (mostly restricted to 3x3 or 4x4), including identity, square, row and column matrices. Transpose of a matrix.
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Matrices Matrix addition, subtraction and multiplication
Assume A, B and C are matrices and r and s are scalars For addition and subtraction: A + B = B + A A + (B + C) = (A + B) + C A − B = A + (−B) −(−A) = A s(A ± B) = sA ± sB (r ± s)A = r A ± sA r(sA) = s(r A) = (rs)A For multiplication: AI = IA = A A(BC) = (AB)C A(B ± C) = AB ± AC (A ± B)C = AC ± BC (sA)B = s(AB) = A(sB) For transposition: (A ± B)T = AT ± BT (sA)T = sAT (AB)T = BTAT Matrices Matrix addition, subtraction and multiplication Common matrix algebraic identities If A is an m × n matrix and B an n × p matrix, then matrix multiplication (C = AB) is defined as:
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Matrices Matrix determinants and inverse
The determinant of a matrix A is denoted det(A) or |A|, is calculated as: 1x1 2x2 3x3 The inverse of a 2x2 or 3x3 matrix is:
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Assumed Maths: Calculus
Assumed mathematical knowledge dealing with basic calculus
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Calculus Basic calculus including: simple differential calculus (rate of change over time of a variable) and integral calculus
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Assumed Maths: Polyhedra
Assumed mathematical knowledge dealing with polygons and polyhedra
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Polygons Definition of a polygon, including edges and vertices, convex and concave, polygon mesh.
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Polyhedra Definition of polyhedra including interior and exterior, polytope (bounded convex polyhedron).
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Assumed Maths: Miscellaneous
Miscellaneous mathematical aspects
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Barycentric Coordinates
Barycentric coordinates parameterize the space formed using a weighted combination of a set of reference points. C Consider two points A and B, any point on the line between A and B can be expressed as P = A + t(B − A) = (1 − t)A + tB or simply as P = uA + vB, where u + v = 1, i.e. P is on the segment AB if and only if 0 ≤ u ≤ 1 and 0 ≤ v ≤ 1. Expressions, as above, in terms of (u,v) are the barycentric coordinates of P with respect to A and B. B A
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Line, Rays, Segments, Planes and Halfspaces
Definition of a line, ray and segment Definition of a plane and half-space Assume A, B and C are defined points and t, u and v are scalars, and n is a normal vector:
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Minkowski Sum and Difference
Basic understanding of the Minkowski sum and Minkowski difference. Appreciate that two point sets intersect if, and only if, their Minkowski difference contains the origin. Assume A and B are two point sets, and a and b are position vectors of points in A and B. The Minkowski sum, A ⊕ B, is defined as the set the Minkowski difference is obtained by adding A to the reflection of B about the origin; that is, A Ѳ B = A ⊕ (−B)
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Voronoi regions Given a set S of points in the plane, the Voronoi region of a point P in S is defined as the set of points in the plane closer to (or as close to) P than to any other points in S. Within a collision detection context, given a polyhedron P, let a feature of P be one of its vertices, edges, or faces. The Voronoi region of a feature of P is then the set of points in space closer to (or as close to) the feature than to any other feature of P.
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Directed reading Directed Reading Directed mathematical reading
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Directed reading Directed reading Read Chapter 3 (pp23-72) of Real Time Collision Detection Read Section 4 (pp ) of Game Engine Architecutre. Read Section 2 (pp15-42) and Section 9 (pp ) of Game Physics Engine Development Consult the excellent Wolfram MathWorld
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To do: Summary Explore linked mathematical resources.
Today we explored: Mathematical knowledge assumed within the module to cover collision detection and rigid body dynamics. To do: Explore linked mathematical resources. Consider how you can best make use of a ‘just-in-time’ approach for mathematical concepts.
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