【CesiumJS-5】绘制动态路线实现飞行航线、汽车轨迹、路径漫游等

实现效果

前言

Cesium中，动态路线绘制的核心是借助CZML格式，CZML是一种用来描述动态场景的JSON数组,可以用来描述点、线、多边形、体、模型及其他图元,同时定义它们是怎样随时间变化的；

CZML主要做三件事：

1.添加模型信息

2.添加路径信息

3.计算速度，修改时间

CZML数据格式

[
  {
    "id": "document",
    "version": "1.0",
    "clock": {
      "interval": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
      "currentTime": "2024-03-13T03:00:00Z",
      "multiplier": 5
    }
  },
  {
    "id": "plane",
    "availability": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
    "viewFrom": {
      cartesian: [-2080, -1715, 779]
    },
    "model": {
      "gltf": "/model/plane.glb",
      "scale": 2
    },
    "orientation": {
      "velocityReference": "#position"
    },
    "path": {
      "material": {
        "solidColor": {
          "color": {
            "interval": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
            "rgba": [0, 0, 205, 255]
          }
        }
      },
      "width": [
        {
          "interval": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
          "number": 2
        }
      ],
      "show": [
        {
          "interval": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
          "boolean": true
        }
      ]
    },
    "position": {
      "interpolationAlgorithm": "LAGRANGE",
      "interpolationDegree": 1,
      "epoch": "2024-03-13T03:00:00Z",
      "cartographicDegrees": []
    }
  }
]

主要有两个对象组成：第一个对象声明czml，第二个对象生成模型。

1. 声明czml

  {
    "id": "document",
    "version": "1.0",
    "clock": {
      "interval": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
      "currentTime": "2024-03-13T03:00:00Z",
      "multiplier": 5
    }
  }

2. 设置相机位置

    "viewFrom": {
      cartesian: [-2080, -1715, 779]
    },

3. 生成场景模型，设置时间范围

  {
    "id": "plane",
    "availability": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
    "model": {
      "gltf": "/model/plane.glb",
      "scale": 2
    }
  }

4. 设置模型运动方向

    "orientation": {
      "velocityReference": "#position"
    },

5. 生成动态路径

    "path": {
      "material": {
        "solidColor": {
          "color": {
            "interval": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
            "rgba": [
              0,
              0,
              205,
              255
            ]
          }
        }
      },
      "width": [
        {
          "interval": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
          "number": 2
        }
      ],
      "show": [
        {
          "interval": "2024-03-13T03:00:00Z/2024-03-13T03:12:50Z",
          "boolean": true
        }
      ]
    },

6. 设置运动路线

cartographicDegrees设置经纬度：4个一组分别是时间，经度，纬度，高度

    "position": {
      "interpolationAlgorithm": "LAGRANGE",
      "interpolationDegree": 1,
      "epoch": "2024-03-13T03:00:00Z",
      "cartographicDegrees": [0, 120.13125463180745, 30.316189813141357, 20]
    }

功能实现

本人在实现功能中没用json格式,而是直接用的数组对象变量，上述中仅做学习记录。

注意: czml只能识别ISO8601日期，需要使用Cesium内置方法转换时间；

1. 将当前时间作为开始时间并将js日期转为儒略日格式

const start = Cesium.JulianDate.fromDate(new Date());

2. 创建czml数组

使用Cesium.JulianDate.toIso8601()方法将时间转为ISO8601日期格式

const czml = [
  {
    id: "document",
    version: "1.0",
    clock: {
      interval: `${Cesium.JulianDate.toIso8601(start, 0)}/${Cesium.JulianDate.toIso8601(Cesium.JulianDate.addSeconds(start, 450, new Cesium.JulianDate()), 0)}`,
      currentTime: `${Cesium.JulianDate.toIso8601(start, 0)}`,
      multiplier: 10,
    }
  },
  {
    id: "plane",
    availability: `${Cesium.JulianDate.toIso8601(start, 0)}/${Cesium.JulianDate.toIso8601(Cesium.JulianDate.addSeconds(start, 450, new Cesium.JulianDate()), 0)}`,
    model: {
      gltf: "/model/plane.glb",
      scale: 2
    },
    // viewFrom: {
    //   cartesian: [-2080, -1715, 779]
    // },
    orientation: {
      velocityReference: "#position"
    },
    path: {
      material: {
        solidColor: {
          color: {
            interval: `${Cesium.JulianDate.toIso8601(start, 0)}/${Cesium.JulianDate.toIso8601(Cesium.JulianDate.addSeconds(start, 450, new Cesium.JulianDate()), 0)}`,
            rgba: [0, 0, 205, 255]
          }
        }
      },
      width: [
        {
          interval: `${Cesium.JulianDate.toIso8601(start, 0)}/${Cesium.JulianDate.toIso8601(Cesium.JulianDate.addSeconds(start, 450, new Cesium.JulianDate()), 0)}`,
          number: 2
        }
      ],
      show: [
        {
          interval: `${Cesium.JulianDate.toIso8601(start, 0)}/${Cesium.JulianDate.toIso8601(Cesium.JulianDate.addSeconds(start, 450, new Cesium.JulianDate()), 0)}`,
          boolean: true
        }
      ]
    },
    position: {
      interpolationAlgorithm: "LAGRANGE",
      interpolationDegree: 1,
      epoch: `${Cesium.JulianDate.toIso8601(start, 0)}`,
      cartographicDegrees: [
        0, 120.13125463180745, 30.316189813141357, 5,
        10, 120.13111416662538, 30.315539106519307, 5,
        20, 120.1309786622693, 30.31489588182787, 5,
        30, 120.13084876734133, 30.314235695359727, 5,
        40, 120.13069473575192, 30.313540629197277, 5,
        50, 120.13054390032266, 30.312912654513724, 5,
        60, 120.13044947371688, 30.312385482730374, 5,
        70, 120.13030971147948, 30.311910736974383, 5,
        80, 120.13009317468772, 30.311390245082837, 5,
        90, 120.12978893985873, 30.310733495046055, 5,
        100, 120.12959024998796, 30.310326531696383, 10,
        110, 120.12938465577722, 30.309954975972268, 30,
        120, 120.12903852757415, 30.309336955328902, 60,
        130, 120.12871206396551, 30.308875801472478, 70,
        140, 120.12838069578686, 30.308490868344943, 70,
        150, 120.12810457466928, 30.308113523536672, 70,
        160, 120.12779772791689, 30.307774086249907, 80,
        170, 120.12737964279644, 30.307483823729378, 80,
        180, 120.1269732925855, 30.307160879171903, 80,
        190, 120.12647213239983, 30.30666310390423, 80,
        200, 120.12546262988464, 30.307181930544864, 80,
        210, 120.1245785033241, 30.307683795316315, 80,
        220, 120.12375576753382, 30.308035432883194, 100,
        230, 120.12308850447974, 30.308497699718018, 100,
        240, 120.12253685192415, 30.308860660895174, 100,
        250, 120.12209783635902, 30.309214249085528, 100,
        260, 120.12124539807733, 30.309730900111948, 120,
        270, 120.12062513785223, 30.30968143768237, 125,
        280, 120.11996146408914, 30.30903962813221, 130,
        290, 120.12080592297113, 30.308199027265523, 135,
        300, 120.1206419712799, 30.307743185311676, 140,
        310, 120.11991139765998, 30.306939478614392, 200,
        320, 120.11894945108537, 30.307236007284757, 220,
        330, 120.11843736124806, 30.307682602103153, 240,
        340, 120.11801295026378, 30.308682424137178, 260,
        350, 120.117608250043, 30.30896814314354, 280,
        360, 120.11756912872843, 30.309470200064347, 300,
        370, 120.11718042273918, 30.310442342271475, 300,
        380, 120.11602779574089, 30.3098989524904, 310,
        390, 120.11550616761767, 30.31093863353403, 310,
        400, 120.11644406776917, 30.31177509905328, 310,
        410, 120.11566744726449, 30.312255943277282, 320,
        420, 120.11627775321915, 30.312631949114188, 320,
        430, 120.11695495518998, 30.313251980473588, 330,
        440, 120.11755845523233, 30.313636377593916, 330,
        450, 120.11843011762987, 30.31389033163698, 340
      ]
    }
  }
]

3. 加载CZML数据并添加到场景中

dataSources：是一个异步Promise，回调参数为我们传入的czml数据；

let dataSource = viewer.dataSources.add(Cesium.CzmlDataSource.load(czml));

4. 相机跟随模型

  dataSource.then(part => {
    // 根据id获取czml中的模型
    let e = part.entities.getById("plane");
    // 相机跟随模型
    viewer.trackedEntity = e;
  });

5. 视角跟随模型

  dataSource.then(part => {
    // 根据id获取czml中的模型
    let e = part.entities.getById("plane");
    // 相机跟随模型
    viewer.trackedEntity = e;

    //++++++++++++++
    // 视角跟随模型
    let prePoint = null; // 前一个点
    viewer.scene.postRender.addEventListener(() => {
      if (e && viewer.clock.shouldAnimate) {
        // 获取当前时间的位置
        let curPoint = e.position.getValue(viewer.clock.currentTime);
        if (prePoint) {
          // 计算heading-代表 Z 轴旋转
          let heading = getHeading(prePoint, curPoint);
          // 计算pitch-代表 Y 轴朝向
          let pitch = Cesium.Math.toRadians(-30.0);
          let range = 100;
          viewer.camera.lookAt(curPoint, new Cesium.HeadingPitchRange(heading, pitch, range));
        }
        // 当前点在下一次渲染时为前一个点
        prePoint = Cesium.Cartesian3.clone(curPoint)
      }
    }) 
  });


function getHeading(pointA, pointB) {
  //建立以点A为原点，X轴为east,Y轴为north,Z轴朝上的坐标系
  const transform = Cesium.Transforms.eastNorthUpToFixedFrame(pointA);
  //向量AB
  const positionvector = Cesium.Cartesian3.subtract(pointB, pointA, new Cesium.Cartesian3());
  //因transform是将A为原点的eastNorthUp坐标系中的点转换到世界坐标系的矩阵
  //AB为世界坐标中的向量
  //因此将AB向量转换为A原点坐标系中的向量，需乘以transform的逆矩阵。
  const vector = Cesium.Matrix4.multiplyByPointAsVector(Cesium.Matrix4.inverse(transform, new Cesium.Matrix4()), positionvector, new Cesium.Cartesian3());
  //归一化
  const direction = Cesium.Cartesian3.normalize(vector, new Cesium.Cartesian3());
  //heading
  const heading = Math.atan2(direction.y, direction.x) - Cesium.Math.PI_OVER_TWO;
  return Cesium.Math.TWO_PI - Cesium.Math.zeroToTwoPi(heading);
}

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