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

``````const vec4 = require('../../maths/vec4')

const cache = new WeakMap()

/**
* Measure the bounding sphere of the given polygon.
* @param {poly3} polygon - the polygon to measure
* @returns {vec4} the computed bounding sphere; center point (3D) and radius
* @alias module:modeling/geometries/poly3.measureBoundingSphere
*/
const measureBoundingSphere = (polygon) => {
const boundingSphere = cache.get(polygon)
if (boundingSphere) return boundingSphere

const vertices = polygon.vertices
const out = vec4.create()

if (vertices.length === 0) {
out[0] = 0
out[1] = 0
out[2] = 0
out[3] = 0
return out
}

// keep a list of min/max vertices by axis
let minx = vertices[0]
let miny = minx
let minz = minx
let maxx = minx
let maxy = minx
let maxz = minx

vertices.forEach((v) => {
if (minx[0] > v[0]) minx = v
if (miny[1] > v[1]) miny = v
if (minz[2] > v[2]) minz = v
if (maxx[0] < v[0]) maxx = v
if (maxy[1] < v[1]) maxy = v
if (maxz[2] < v[2]) maxz = v
})

out[0] = (minx[0] + maxx[0]) * 0.5 // center of sphere
out[1] = (miny[1] + maxy[1]) * 0.5
out[2] = (minz[2] + maxz[2]) * 0.5
const x = out[0] - maxx[0]
const y = out[1] - maxy[1]
const z = out[2] - maxz[2]
out[3] = Math.sqrt(x * x + y * y + z * z) // radius of sphere

cache.set(polygon, out)

return out
}

module.exports = measureBoundingSphere
``````