How to use js to judge whether it is legal to form a single polygon according to its coordinates

This article introduces how to use js to judge whether it is legal to form a single polygon according to coordinates. The content is very detailed. Interested friends can use it for reference. I hope it will be helpful to you.

Preface

Demand: judge whether the fence drawn by the user is legal in Amap.

Core solution: if the two adjacent segments are judged in reverse order, whether there is an intersection or not, the non-adjacent segments do not intersect.

Install npm install @ turf/helpers @ turf/line-intersect Code / * geometric Geometry tools Library * @ author maybe * @ license https://gitee.com/null_639_5368 * / import * as turf from "@ turf/helpers" import lineIntersect from "@ turf/line-intersect" / * coordinate transition segment * @ param {*} path * @ returns {arr} * / export function pathToLines (path) {const lines = [] Path.forEach ((p, pi) = > {let line; if (pi = = path.length-1) {line = turf.lineString ([path [pi], path [0]]); lines.push (line) return;} line = turf.lineString ([path [pi], path [pi + 1]]) Lines.push (line)}) / / console.log (JSON.stringify (lines)) return lines } / * determine whether a single polygon composed of coordinates is legal * @ param {*} path * @ description Please pass a similar two-dimensional array * @ returns {boolean} * / export function isTruePolygon (path) {/ / judgment array and the length of the array is less than 3 does not constitute a necessary condition to satisfy a facet termination if (! Array.isArray (path) | | path.length

< 3) return false; // 具体坐标也需是一个一维数组，并且数组的长度等于2 if (!path.every(item =>

Array.isArray (item) & & item.length = = 2) return false; / / convert coordinates to line segment const lines = pathToLines (path); / / whether it is legal to mark let isTrue = true; / / verify function function check () {/ / reverse loop for (let I = lines.length-1; I > = 0 Const lineNextIndex -) {/ / baseline segment const line = lines [I]; const lineNextIndex = I = 0? Lines.length-1: I-1; const lineLastIndex = I = = lines.length-1? 0: I + 1; const lineNext = lines [lineNextIndex]; const lineLast = lines [lineLastIndex] / / two adjacent segments must have intersections if (! isIntersect (line, lineNext) | |! isIntersect (line, lineLast)) {console.log ('adjacent segments must have intersections', line, lineNext, lineLast, isIntersect (line, lineNext), isIntersect (line, lineLast) isTrue = false Return;} / / non-adjacent segments must have no intersection const noNearLines = lines.filter ((item, I) = > I! = = lineNextIndex & & I! = = lineLastIndex) NoNearLines.forEach (le = > {if (isIntersect (line, le)) {console.log ('non-adjacent segments must have no intersection') isTrue = false; return;}})} check (); isTrue? Console.info ('legal polygons'): console.log (illegal polygons) return isTrue;} function isIntersect (line1, line2) {return lineIntersect (line1, line2) .features.length > 0 } export default {pathToLines, isTruePolygon,} Test import {isTruePolygon} from'. / geometric'const path_false = [[116.403322, 39.920255], [116.385726, 39.909893], [116.410703, 39.897555], [116.402292, 39.892353], [116.389846, 39.891365]] const path_true = [[116.403322, 39.920255], [116.410703, 39.897555], [116.402292] 39.892353], [116.389846, 39.891365]] console.log (isTruePolygon (path_true)) / / trueconsole.log (isTruePolygon (path_false)); / / false is here about how to use js to determine whether it is legal to form a single polygon according to coordinates. I hope the above content can be helpful to everyone and learn more knowledge. If you think the article is good, you can share it for more people to see.