GCSGUI/src/utils/map/geocomputation.ts

/*
 * @Author: cbwu 504-wuchengbo@htsdfp.com
 * @Date: 2024-03-22 15:42:49
 * @LastEditors: cbwu
 * @LastEditTime: 2024-04-01 14:05:43
 * @Description: 地理计算
 */
import { Cartesian3, Math as Cesium_Math } from 'cesium'
/**
 * 计算空间中一点到一条直线的最短距离的交点（在不考虑地球曲率的情况下）
 * @param lineStart 直线的起点：[longitude1, latitude1, height1]
 * @param lineEnd 直线的终点:[longitude2, latitude2, height2]
 * @param point 空间中的点:[[longitude3, latitude3, height3]]
 * @returns 最近的交点
 */
function getClosestPoint(
  lineStart: Cartesian3,
  lineEnd: Cartesian3,
  point: Cartesian3,
): Cartesian3 {
  // 计算直线方向向量
  const lineDirection = new Cartesian3()
  Cartesian3.subtract(lineEnd, lineStart, lineDirection)
  Cartesian3.normalize(lineDirection, lineDirection)

  // 计算点到直线起点的向量
  const pointToStart = new Cartesian3()
  Cartesian3.subtract(point, lineStart, pointToStart)

  // 计算投影长度，即点到直线的向量在直线方向向量上的分量长度
  const projectionLength = Cartesian3.dot(pointToStart, lineDirection)

  // 使用标量乘法和向量加法确定交点
  const closestPoint = new Cartesian3()
  Cartesian3.multiplyByScalar(lineDirection, projectionLength, closestPoint)
  Cartesian3.add(lineStart, closestPoint, closestPoint)
  return closestPoint
}

/**
 * 判断一个点是否在直线上（在不考虑地球曲率的情况下）
 * @param lineStart 直线的起点：[longitude1, latitude1, height1]
 * @param lineEnd 直线的起点：[longitude2, latitude2, height2]
 * @param pointToCheck 直线的起点：[longitude3, latitude3, height3]
 * @param tolerance 容差
 * @returns 是否在线段上
 */
function isOnLineSegment(
  lineStart: Cartesian3,
  lineEnd: Cartesian3,
  pointToCheck: Cartesian3,
  tolerance: number = Cesium_Math.EPSILON1,
): boolean {
  const dist_AP = Cartesian3.distance(lineStart, pointToCheck)
  const dist_BP = Cartesian3.distance(lineEnd, pointToCheck)
  const dist_AB = Cartesian3.distance(lineStart, lineEnd)

  const isCollinear = Math.abs(dist_AP + dist_BP - dist_AB) < tolerance
  return isCollinear
  /*
  const startToEnd = new Cartesian3()
  const startToPoint = new Cartesian3()
  const endToPoint = new Cartesian3()

  // 计算向量
  Cartesian3.subtract(lineEnd, lineStart, startToEnd)
  Cartesian3.subtract(pointToCheck, lineStart, startToPoint)
  Cartesian3.subtract(pointToCheck, lineEnd, endToPoint)

  // 判断共线
  const cross = Cartesian3.cross(startToEnd, startToPoint, new Cartesian3())
  console.log('cross:' + Cartesian3.magnitude(cross).toString())
  // Math.EPSILON6 是一个非常小的值，用来防止浮点数计算的误差
  const isCollinear = Cartesian3.magnitude(cross) < tolerance

  // 判断点是否在线段之间
  let isBetween = false
  if (isCollinear) {
    const dotProduct1 = Cartesian3.dot(startToEnd, startToPoint)
    const dotProduct2 = Cartesian3.dot(startToEnd, endToPoint)
    isBetween = dotProduct1 >= 0 && dotProduct2 <= 0
  }
  return isBetween
  */
}


export { getClosestPoint, isOnLineSegment }