calibrate.js

var compass = require("./build/Release/binding");

var SAMPLE_RATE = 30;

var min = {
  x: Infinity,
  y: Infinity,
  z: Infinity,
};
var max = {
  x: -Infinity,
  y: -Infinity,
  z: -Infinity,
};
var count = 0;
var MAX_NUM = 1000;

compass.initialize();

console.log(
  "This script will calculate the offset & scale matrixes for correcting magnetometer output."
);
console.log(
  "Rotate the magnetometer around all 3 axes, until the min and max values don't change anymore."
);
console.log(
  "    x        y        z      min x    min y    min z    max x    max y    max z"
);

setInterval(function () {
  if (count++ > MAX_NUM) {
    wrapUp();
  }

  var vals = compass.readRawData();

  min.x = Math.min(min.x, vals.x);
  min.y = Math.min(min.y, vals.y);
  min.z = Math.min(min.z, vals.z);

  max.x = Math.max(max.x, vals.x);
  max.y = Math.max(max.y, vals.y);
  max.z = Math.max(max.z, vals.z);

  process.stdout.write(
    p(vals.x) +
      p(vals.y) +
      p(vals.z) +
      p(min.x) +
      p(min.y) +
      p(min.z) +
      p(max.x) +
      p(max.y) +
      p(max.z) +
      "\r"
  );
}, SAMPLE_RATE);

function p(num) {
  var str = num.toFixed(3);
  while (str.length <= 7) {
    str = " " + str;
  }
  return str + " ";
}

var offset = {};
var scale = {};
function calcCalibration() {
  offset = {
    x: (min.x + max.x) / 2,
    y: (min.y + max.y) / 2,
    z: (min.z + max.z) / 2,
  };
  var vmax = {
    x: max.x - (min.x + max.x) / 2,
    y: max.y - (min.y + max.y) / 2,
    z: max.z - (min.z + max.z) / 2,
  };
  var vmin = {
    x: min.x - (min.x + min.x) / 2,
    y: min.y - (min.y + min.y) / 2,
    z: min.z - (min.z + min.z) / 2,
  };
  var avg = {
    x: (vmax.x - vmin.x) / 2,
    y: (vmax.y - vmin.y) / 2,
    z: (vmax.z - vmin.z) / 2,
  };
  var avg_radius = (avg.x + avg.y + avg.z) / 2;
  scale = {
    x: avg_radius / avg.x,
    y: avg_radius / avg.y,
    z: avg_radius / avg.z,
  };
}

function wrapUp(err) {
  if (err) {
    console.error(err);
  } else {
    console.log("\n\nCalibrated values:");
    calcCalibration();
    console.log({
      offset: offset,
      scale: scale,
    });
  }

  var exit = process.exit;
  exit(0);
}