77 lines
1.7 KiB
Plaintext
77 lines
1.7 KiB
Plaintext
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import Mathlib.Data.Real.Basic
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import Mathlib.Data.Real.Sqrt
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import Common.Real.Trigonometry
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/-! # Common.Geometry.Point
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A representation of a point in the two-dimensional Cartesian plane.
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-/
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namespace Geometry
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structure Point where
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x : ℝ
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y : ℝ
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noncomputable instance : DecidableEq Point := by
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intro p₁ p₂
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have ⟨x₁, y₁⟩ := p₁
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have ⟨x₂, y₂⟩ := p₂
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if hp : x₁ = x₂ ∧ y₁ = y₂ then
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rw [hp.left, hp.right]
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exact isTrue rfl
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else
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rw [not_and_or] at hp
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refine isFalse ?_
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intro h
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injection h with hx hy
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apply Or.elim hp
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· intro nx
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exact absurd hx nx
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· intro ny
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exact absurd hy ny
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namespace Point
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/--
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The function mapping a `Point` to a `2`-tuple of reals.
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-/
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def toTuple (p : Point) : ℝ × ℝ := (p.x, p.y)
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/--
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The function mapping a `2`-tuple of reals to a `Point`.
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-/
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def fromTuple (p : ℝ × ℝ) : Point := Point.mk p.1 p.2
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/--
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An isomorphism between a `Point` and a `2`-tuple.
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-/
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def isoTuple : Point ≃ ℝ × ℝ :=
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{
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toFun := toTuple,
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invFun := fromTuple,
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left_inv := by
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unfold Function.LeftInverse fromTuple toTuple
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simp,
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right_inv := by
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unfold Function.RightInverse Function.LeftInverse fromTuple toTuple
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simp
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}
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/--
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The length of the straight line segment connecting points `p` and `q`.
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-/
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noncomputable def dist (p q : Point) :=
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Real.sqrt ((abs (q.x - p.x)) ^ 2 + (abs (q.y - p.y)) ^ 2)
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/--
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The undirected angle at `p₂` between the line segments to `p₁` and `p₃`. If
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either of those points equals `p₂`, this is `π / 2`.
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-/
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noncomputable def angle (p₁ p₂ p₃ : Point) : ℝ :=
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Real.euclideanAngle (toTuple p₁) (toTuple p₂) (toTuple p₃)
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end Point
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end Geometry
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