2:1 isometric grid calculator

calculateIsoGrid.js

/**
 * Calculate a 2:1 iso grid for specific sizes.
 *
 * @author Henning Pohlmeyer
 *
 * @param  {number} smallestValue The smalles value to use in the grid.
 * @return {object}               The grid spacing value and rotate and
 *                                shear values for each plane.
 */
function calculateIsoGrid(smallestValue) {
	const a = smallestValue || 1;
  const b = a * 2;
  const c = Math.sqrt(Math.pow(a, 2) + Math.pow(b, 2));

  const radians = Math.atan(a/b);
  const degree = radians * 180 / Math.PI;

  return {
    gridSpacing: `${c}px`,
    topPlane: {
      rotate: `${degree}°`,
      shear: `${90 - 2 * degree}°`,
    },
    rightPlane: {
      rotate: `${degree}°`,
      shear: `${-degree}°`,
    },
    leftPlane: {
      rotate: `${-degree}°`,
      shear: `${degree}°`,
    },
  };
}