Triangle-completion NPM

triangle-completion

Calc a triangle from a partial spec. Basic trig nicely packaged.

Usage

import solveTriangle, { TriangleError } from 'trig';
console.log(solveTriangle({ alpha:60, beta: 30, B: 1 }));
{
  alpha: 60,
  beta: 30,
  gamma: 90,
  A: 1.7320508075688774,
  B: 1
  C: 2.0000000000000004,
}
console.log(solveTriangle({ A:1, C:2, alpha: 10 }));
{
  A: 1,
  B: 2.907370933399707
  C: 3.7264028721887454,
  alpha: 10,
  beta: 30.32203701650613,
  gamma: 139.67796298349387,
  alt: {
    A: 1,
    B: 2,
    C: 2.907370933399707,
    alpha: 10,
    beta: 20.32203701650614
    gamma: 149.67796298349387,
  },
}

Specifications use alpha, beta, gamma for angles and A, B, C for the corresponding opposite sides. As shown, an SSA spec involving an acute angle generates both possible solutions.

Invalid inputs (zero/NaN/undefined, or unsolvable specifications) throw TriangleError, trivially derived from Error. null inputs propogate to the output without throwing an error.

Optimizing

solveTriangle analyzes and mutates the input spec to match up with one of several solver functions. You can import and invoke these solver functions directly, saving both the cost of the analysis (for sure a few conditional evaluations and likely a few rotate/invert object manipulations) and the cost in time and space of importing unused logic. The individual solvers are named for the inputs they expect as follows:

Angle-Angle-Side: aas.js solveGammaAlphaC({ gamma: 20, alpha: 80, C: 3 })
Angle-Side-Angle: asa.js solveAlphaBGamma({ alpha: 80, B: 3, gamma: 20 })
Side-Angle-Side: sas.js solveAGammaB({ A: 1, gamma: 20, B: 3 })
Side-Side-Side: sss.js solveABC({ A: 1, B: 3, C: 5 })
Side-Side-Angle: ssa.js solveABAlpha({ A: 1, B: 3, alpha: 40 })

This last is ambiguous if the angle is acute. As shown above, the solution includes an "alt" key giving another matching triangle. Nothing determines which solution is presented as "alt".

There are also some trivial support functions in common.js, but it's unlikely they'll be of much interest on their own.