turf.js实现多边形分割

Posted 2021-12-08 LZU-GIS

概述

在做编辑的时候，难免会遇到多边形的分割问题，本文用turf.js实现此功能。

效果

实现思路

实现代码

function polygonCut(poly, line, tolerance = .001, toleranceType ='kilometers') {
  // 1. 条件判断
  if (poly.geometry === void 0 || poly.geometry.type !== 'Polygon')
    throw ('传入的必须为polygon');
  if (line.geometry === void 0 || line.geometry.type.toLowerCase().indexOf('linestring') === -1)
    throw ('传入的必须为linestring');
  if (line.geometry.type === "LineString") {
    if (turf.booleanPointInPolygon(turf.point(line.geometry.coordinates[0]), poly)
      || turf.booleanPointInPolygon(turf.point(line.geometry.coordinates[line.geometry.coordinates.length - 1]), poly))
      throw ('起点和终点必须在多边形之外');
  }
  // 2. 计算交点，并把线的点合并
  let lineIntersect = turf.lineIntersect(line, poly);
  const lineExp = turf.explode(line);
  for (let i = 0; i < lineExp.features.length - 1; i++) {
    lineIntersect.features.push(turf.point(lineExp.features[i].geometry.coordinates));
  }
  // 3. 计算线的缓冲区
  const lineBuffer = turf.buffer(line, tolerance, {
    units: toleranceType
  });
  // 4. 计算线缓冲和多边形的difference，返回"MultiPolygon"，所以将其拆开
  const _body = turf.difference(poly, lineBuffer);
  let pieces = [];
  if (_body.geometry.type === 'Polygon') {
    pieces.push(turf.polygon(_body.geometry.coordinates));
  } else {
    _body.geometry.coordinates.forEach(function (a) { pieces.push(turf.polygon(a)) });
  }
  // 5. 处理点数据
  for (p in pieces) {
    const piece = pieces[p];
    for (let c in piece.geometry.coordinates[0]) {
      const coord = piece.geometry.coordinates[0][c];
      const p = turf.point(coord);
      for (let lp in lineIntersect.features) {
        const lpoint = lineIntersect.features[lp];
        if (turf.distance(lpoint, p, toleranceType) <= tolerance*2) {
          piece.geometry.coordinates[0][c] = lpoint.geometry.coordinates;
        }
      }
    }
  }
  // 6. 过滤掉重复点
  for (p in pieces) {
    const coords = pieces[p].geometry.coordinates[0]
    pieces[p].geometry.coordinates[0] = filterDuplicatePoints(coords);
  }
  // 7. 将属性赋予每一个polygon，并处理id
  pieces.forEach((a, index) => {
    a.properties = Object.assign({}, poly.properties)
    a.properties.id += `-${index}`
  });
  return turf.featureCollection(pieces);
}