Cesium计算范围(十三)

  function bounds(positions = [], expand = 0) {
    let minLng = 180
    let minLat = 90
    let maxLng = -180
    let maxLat = -90
    positions.forEach(item => {
      minLng = Math.min(minLng, item.lng || item.x)
      minLat = Math.min(minLat, item.lat || item.y)
      maxLng = Math.max(maxLng, item.lng || item.x)
      maxLat = Math.max(maxLat, item.lat || item.y)
    })

    if (expand > 0) {
      let diffLng = Math.abs(maxLng - maxLng)
      let diffLat = Math.abs(maxLat - minLat)
      minLng -= diffLng * expand
      minLat -= diffLat * expand
      maxLng += diffLng * expand
      maxLat += diffLat * expand
    }
    return {
      west: minLng,
      south: minLat,
      east: maxLng,
      north: maxLat
    }
}