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index.js
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index.js
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const _ = require('lodash')
module.exports = (options) =>{
options = options || {};
const x = options.x || 'longitude';
const y = options.y || 'latitude';
const isLeft = (p0, p1 , p2) => {
return (p1[x] - p0[x]) * (p2[y] - p0[y]) - (p2[x] - p0[x]) * (p1[y] - p0[y]);
}
const sortByX = (a, b) => {
return a[x] - b[x];
}
const sortByY = (a, b) => {
return a[y] - b[y];
}
return (points, sort) => {
if(!(points instanceof Array)) {
throw new TypeError('points must be an array');
}
if(points.length < 2) {
return [];
}
if(sort) {
points = _.orderBy(points, [x, y], ['asc', 'asc']);
}
let bot = 0;
let top = -1;
let hull = [];
let minMin = 0;
let xMin = points[0][x];
let i = 1;
for(;i < points.length; i++) {
if(points[i][x] !== xMin) {
break;
}
}
minMax = i - 1;
if(minMax === points.length - 1) {
hull[++top] = points[minMin];
if(points[minMax][y] !== points[minMin][y])
hull[++top] = points[minMax];
hull[++top] = points[minMin];
return hull;
}
let maxMin, maxMax = points.length - 1;
let xMax = points[points.length - 1][x];
for(i = points.length -2; i >= 0; i--) {
if(points[i][x] !== xMax) {
break;
}
}
maxMin = i + 1;
hull[++top] = points[minMin];
i = minMax;
while (++i <= maxMin) {
if (isLeft(points[minMin],points[maxMin], points[i]) >=0 && i < maxMin) {
continue;
}
while (top > 0) {
if (isLeft(hull[top - 1], hull[top], points[i]) > 0) {
break;
} else {
top--;
}
}
hull[++top] = points[i];
}
if (maxMax !== maxMin) {
hull[++top] = points[maxMax];
}
bot = top;
i = maxMin;
while (--i >= minMax) {
if (isLeft(points[maxMax], points[minMax], points[i]) >= 0 && i > minMax) {
continue;
}
while (top > bot) {
if (isLeft(hull[top - 1], hull[top], points[i]) > 0) {
break;
} else {
top--;
}
}
if (points[i][x] === hull[0][x] && points[i][y] === hull[0][y]) {
return hull;
}
hull[++top] = points[i];
}
if (minMax !== minMin) {
hull[++top] = points[minMin];
}
return hull;
}
}