* Simple Line Fitting

 * Keith J. O'Hara <kohara2@swarthmore.edu>

 * March 2024

 */

​

// uses ML.js https://github.com/mljs/ml?tab=readme-ov-file

// because jsfeat svd is broken :(

​

// the points we are fitting

let p = [];

​

function setup() {

  createCanvas(640, 480);

  noStroke();

  background(255);

}

​

function mouseDragged() {

  p.push(new p5.Vector(mouseX, mouseY, 1));

}

​

function estimate_least_squares() {

  let x = new p5.Vector(0, 0, 0);

​

  if (p.length >= 2) {

    as = []

    bs = []

    // Creates the estimation matrix

    for (let i = 0; i < p.length; i++)     {

      as.push([p[i].x, 1]);

      bs.push([p[i].y]);

    }

    let mls_a = new ML.Matrix(as);

    let mls_b = new ML.Matrix(bs);

    let mls_x = ML.MatrixLib.solve(mls_a, mls_b);

    let a = mls_x.data[0][0];

    let b =  -1; 

    let c = mls_x.data[1][0];

    x = new p5.Vector(a, b, c);

  }

  return x;

}

​

function draw() {

  background(255);

  stroke(0);

  fill(0);

  for (let i = 0; i < p.length; i++) {

    ellipse(p[i].x, p[i].y, 5, 5);

  }

​

  if (p.length >= 2) {

    stroke(255, 0, 0);

    strokeWeight(2);

    let ln = estimate_least_squares();

    plotLine(ln);

    let tot = 0;

    for (let i = 0; i < p.length; i++) {

      let error = ln.dot(p[i]);

      tot += sq(error);

      // show error

      strokeWeight(0.5);

      stroke(200, 0, 0);

      line(p[i].x, p[i].y, p[i].x, p[i].y + error);    

    }

    textSize(24);

    text("total error^2 = " + round(tot), 20, 20);

  }

}

​

​

function plotLine(v) {

  if (abs(v.x) < abs(v.y)) {

    // mostly horizontal

    line(0, v.z/-v.y, width, (v.x*width + v.z)/-v.y);

  }

  else {

    //mostly vertical

    line(v.z/-v.x, 0, (v.y * height + v.z)/-v.x, height);

  }

}