# modeling/src/geometries/poly3/measureArea.js

``````const plane = require('./plane')

/**
* Measure the area of the given polygon.
* @see 2000 softSurfer http://geomalgorithms.com
* @param {poly3} polygon - the polygon to measure
* @return {Number} area of the polygon
* @alias module:modeling/geometries/poly3.measureArea
*/
const measureArea = (polygon) => {
const n = polygon.vertices.length
if (n < 3) {
return 0 // degenerate polygon
}
const vertices = polygon.vertices

// calculate a normal vector
const normal = plane(polygon)

// determine direction of projection
const ax = Math.abs(normal[0])
const ay = Math.abs(normal[1])
const az = Math.abs(normal[2])

if (ax + ay + az === 0) {
// normal does not exist
return 0
}

let coord = 3 // ignore Z coordinates
if ((ax > ay) && (ax > az)) {
coord = 1 // ignore X coordinates
} else
if (ay > az) {
coord = 2 // ignore Y coordinates
}

let area = 0
let h = 0
let i = 1
let j = 2
switch (coord) {
case 1: // ignore X coordinates
// compute area of 2D projection
for (i = 1; i < n; i++) {
h = i - 1
j = (i + 1) % n
area += (vertices[i][1] * (vertices[j][2] - vertices[h][2]))
}
area += (vertices[0][1] * (vertices[1][2] - vertices[n - 1][2]))
// scale to get area
area /= (2 * normal[0])
break

case 2: // ignore Y coordinates
// compute area of 2D projection
for (i = 1; i < n; i++) {
h = i - 1
j = (i + 1) % n
area += (vertices[i][2] * (vertices[j][0] - vertices[h][0]))
}
area += (vertices[0][2] * (vertices[1][0] - vertices[n - 1][0]))
// scale to get area
area /= (2 * normal[1])
break

case 3: // ignore Z coordinates
default:
// compute area of 2D projection
for (i = 1; i < n; i++) {
h = i - 1
j = (i + 1) % n
area += (vertices[i][0] * (vertices[j][1] - vertices[h][1]))
}
area += (vertices[0][0] * (vertices[1][1] - vertices[n - 1][1]))
// scale to get area
area /= (2 * normal[2])
break
}
return area
}

module.exports = measureArea
``````