js 求multipolyline 折中点

你可以使用以下代码来找到 multipolyline 的折中点：

function findMidpoint(multipolyline) {
  let totalLength = 0;
  let lengths = [];

  // 计算multipolyline每个线段的长度和总长度
  for (let i = 0; i < multipolyline.length; i++) {
    let polyline = multipolyline[i];
    let length = 0;
    for (let j = 1; j < polyline.length; j++) {
      let p1 = polyline[j - 1];
      let p2 = polyline[j];
      length += Math.sqrt(Math.pow(p2[0] - p1[0], 2) + Math.pow(p2[1] - p1[1], 2));
    }
    totalLength += length;
    lengths.push(length);
  }

  // 找到总长度的一半
  let halfLength = totalLength / 2;
  let currentLength = 0;
  let currentSegment = 0;

  // 找到折中点所在的线段和该线段上的位置
  for (let i = 0; i < lengths.length; i++) {
    currentLength += lengths[i];
    if (currentLength > halfLength) {
      currentSegment = i;
      break;
    }
  }

  // 计算折中点的坐标
  let polyline = multipolyline[currentSegment];
  let remainingLength = halfLength - (currentLength - lengths[currentSegment]);
  let length = 0;
  for (let j = 1; j < polyline.length; j++) {
    let p1 = polyline[j - 1];
    let p2 = polyline[j];
    let segmentLength = Math.sqrt(Math.pow(p2[0] - p1[0], 2) + Math.pow(p2[1] - p1[1], 2));
    if (length + segmentLength > remainingLength) {
      let ratio = (remainingLength - length) / segmentLength;
      let x = p1[0] + (p2[0] - p1[0]) * ratio;
      let y = p1[1] + (p2[1] - p1[1]) * ratio;
      return [x, y];
    }
    length += segmentLength;
  }

  return null;
}

这个函数接受一个 multipolyline 参数，其中每个元素都是一个多段折线，每个折线都是由一组点表示的数组。它将返回折中点的坐标。如果无法计算折中点，则返回 null