使用Unity做游戏开发，那么它的一些基本概念不可不知。

场景

游戏对象

组件

资产

序列化和反序列化

参考文献

1. Unity游戏开发者需知的基本概念,by Eyas.

Cesium在很早之前就支持GLTF模型动画，例如：

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var czml = [
  {
    id: "document",
    name: "CZML Model",
    version: "1.0",
  },
  {
    id: "aircraft model",
    name: "Cesium Air",
    position: {
      cartographicDegrees: [-77, 37, 10000],
    },
    model: {
      gltf: "../SampleData/models/CesiumAir/Cesium_Air.glb",
      scale: 2.0,
      minimumPixelSize: 128,
    },
  },
];

var viewer = new Cesium.Viewer("cesiumContainer", {
  shouldAnimate: true,
});

var dataSourcePromise = viewer.dataSources.add(
  Cesium.CzmlDataSource.load(czml)
);

这种方法存在一定局限性，只能支持全局动画，不能控制动画的起止。但最近版本中，Cesium进行了一定改进，可以支持在一定程度上控制GLTF动画了。示例代码如下：

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var czml = [
  {
    id: "document",
    name: "CZML Model",
    version: "1.0",
    clock: {
      interval: "2019-06-01T16:00:00Z/2019-06-01T16:10:00Z",
      currentTime: "2019-06-01T16:00:00Z",
      multiplier: 60,
      range: "LOOP_STOP",
      step: "SYSTEM_CLOCK_MULTIPLIER",
    },
  },
  {
    id: "test model",
    name: "Cesium Air",
    position: {
      cartographicDegrees: [-77, 37, 10000],
    },
    model: {
      gltf: "https://assets.agi.com/models/launchvehicle.glb",
      scale: 2.0,
      minimumPixelSize: 128,
      runAnimations: false,
      articulations: {
        "Fairing Open": {
          epoch: "2019-06-01T16:00:00Z",
          number: [0, 0, 600, 120],
        },
        "Fairing Separate": {
          epoch: "2019-06-01T16:00:00Z",
          number: [0, 0, 400, -50],
        },
        "Fairing Drop": {
          epoch: "2019-06-01T16:00:00Z",
          interpolationAlgorithm: "LAGRANGE",
          interpolationDegree: 2,
          number: [0, 0, 80, 0, 100, 0, 120, -1, 600, -120],
        },
      },
    },
  },
];

var viewer = new Cesium.Viewer("cesiumContainer", {
  shouldAnimate: true,
});

var dataSourcePromise = viewer.dataSources.add(
  Cesium.CzmlDataSource.load(czml)
);

dataSourcePromise
  .then(function (dataSource) {
    viewer.trackedEntity = dataSource.entities.getById("test model");
  })
  .otherwise(function (error) {
    console.error(error);
  });

这段示例代码的原理还有待分析，我将launchvehicle.glb导入blender 2.90中，但并没有看到上述代码中的三段动画。按照链接Model Articulations “Number” variable的说法，这三段动画是通过GLTF扩展实现。

参考链接

1. Model Articulations “Number” variable,by cesium.
2. glTF 2.0 Quick Reference Guide ,by KhronosGroup.
3. glTF,by KhronosGroup.
4. Cesium Model Articulations,by cesium.

为了使Cesium与整个网页的背景融合，需要去掉Cesium的黑色星空背景，具体方法如下：

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viewer.scene.skyBox.destroy();
viewer.scene.skyBox = undefined;
viewer.scene.sun.destroy();
viewer.scene.sun = undefined;
viewer.scene.moon.destroy();
viewer.scene.moon = undefined;
viewer.scene.skyAtmosphere.destroy();
viewer.scene.skyAtmosphere = undefined;

viewer.scene.backgroundColor = new Cesium.Color(0, 0, 0, 0);

参考链接

1. Scene Background Transparent,by cesium dev.

Cesium样条插值主要有三种：Linear、Lagrange、Hermite。理解Cesium样条插值对生成平滑飞行路径十分关键。

插值概念

在数学的数值分析领域中，内插或称插值（英语：interpolation）是一种通过已知的、离散的数据点，在范围内推求新数据点的过程或方法。求解科学和工程的问题时，通常有许多数据点借由采样、实验等方法获得，这些数据可能代表了有限个数值函数，其中自变量的值。而根据这些数据，我们往往希望得到一个连续的函数（也就是曲线）；或者更密集的离散方程与已知数据互相吻合，这个过程叫做拟合。

与插值密切相关的另一个问题是通过简单函数逼近复杂函数。假设给定函数的公式是已知的，但是太复杂以至于不能有效地进行评估。来自原始函数的一些已知数据点，或许会使用较简单的函数来产生插值。当然，若使用一个简单的函数来估计原始数据点时，通常会出现插值误差；然而，取决于该问题领域和所使用的插值方法，以简单函数推得的插值数据，可能会比所导致的精度损失更大。

在数值分析这个数学分支中，样条插值是使用一种名为样条的特殊分段多项式进行插值的形式。由于样条插值可以使用低阶多项式样条实现较小的插值误差，这样就避免了使用高阶多项式所出现的龙格现象，所以样条插值得到了流行。

插值定义

给定$n$个离散数据点（称为节点）${\displaystyle (x_{k},y_{k})}(x_{k},y_{k})，{\displaystyle k=1,2,…,n}$。对于${\displaystyle x,(x\neq x_{k},k=1,2,…n)}$，求${\displaystyle x}$所对应的$y$的值称为内插。

$f(x)$为定义在区间$[a,b]$上的函数。${\displaystyle x_{1},x_{2},x_{3}…x_{n}}$为$[a,b]$上 $n$ 个互不相同的点，$G$ 为给定的某一函数类。若$G$ 上有函数$g(x)$ 满足：

$$g(x_{i})=f(x_{i}),k=1,2,…n$$

则称 $g(x)$为 $f(x)$ 关于节点 $x_{1},x_{2},x_{3}…x_{n}$ 在 $G$ 上的插值函数。

参考链接

1. Cesium专栏-样条插值(平滑路径、飞行动画，源码下载),by GIS之家.
2. Cesium的Property机制总结,by vtxf.
3. 插值,by wikipedia.
4. 样条插值,by wikipedia.

Cesium摄像头进入地面下的Bug已经在Cesium 1.66版本中修复。

1.66.0 - 2020-02-03

Deprecated ⏳

• The property Scene.sunColor has been deprecated and will be removed in Cesium 1.69. Use scene.light.color and scene.light.intensity instead. #8493

Additions 🎉

• useBrowserRecommendedResolution flag in Viewer and CesiumWidget now defaults to true. This ensures Cesium rendering is fast and smooth by default across all devices. Set it to false to always render at native device resolution instead at the cost of performance on under-powered devices. #8548
• Cesium now creates a WebGL context with a powerPreference value of high-performance. Some browsers use this setting to enable a second, more powerful, GPU. You can set it back to default, or opt-in to low-power mode, by passing the context option when creating a Viewer or CesiumWidget instance:

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  var viewer = new Viewer('cesiumContainer', { contextOptions : { webgl : { powerPreference: 'default' } } });

• Added more customization to Cesium’s lighting system. #8493
  • Added Light, DirectionalLight, and SunLight classes for creating custom light sources.
  • Added Scene.light for setting the scene’s light source, which defaults to a SunLight.
  • Added Globe.dynamicAtmosphereLighting for enabling lighting effects on atmosphere and fog, such as day/night transitions. It is true by default but may be set to false if the atmosphere should stay unchanged regardless of the scene’s light direction.
  • Added Globe.dynamicAtmosphereLightingFromSun for using the sun direction instead of the scene’s light direction when Globe.dynamicAtmosphereLighting is enabled. See the moonlight example in the Lighting Sandcastle example.
  • Primitives and the globe are now shaded with the scene light’s color.
• Updated SampleData models to glTF 2.0. #7802
• Added Globe.showSkirts to support the ability to hide terrain skirts when viewing terrain from below the surface. #8489
• Added minificationFilter and magnificationFilter options to Material to control texture filtering. #8473
  Updated earcut to 2.2.1. #8528
• Added a font cache to improve label performance. #8537

Fixes 🔧

• Fixed a bug where the camera could go underground during mouse navigation. #8504
• Fixed a bug where rapidly updating a PolylineCollection could result in an instanceIndex is out of range error. #8546
• Fixed issue where RequestScheduler double-counted image requests made via createImageBitmap. #8162
• Reduced Cesium bundle size by avoiding unnecessarily importing Cesium3DTileset in Picking.js. #8532
• Fixed a bug where files with backslashes were not loaded in KMZ files. #8533
• Fixed WebGL warning message about EXT_float_blend being implicitly enabled. #8534
• Fixed a bug where toggling point cloud classification * visibility would result in a grey screen on Linux / Nvidia. #8538
• Fixed a bug where a point in a PointPrimitiveCollection was rendered in the middle of the screen instead of being clipped. #8542
• Fixed a crash when deleting and re-creating polylines from CZML. ReferenceProperty now returns undefined when the target entity or property does not exist, instead of throwing. #8544
• Fixed terrain tile picking in the Cesium Inspector. #8567
• Fixed a crash that could occur when an entity was deleted while the corresponding Primitive was being created asynchronously. #8569
• Fixed a crash when calling camera.lookAt with the origin (0, 0, 0) as the target. This could happen when looking at a tileset with the origin as its center. #8571
• Fixed a bug where camera.viewBoundingSphere was modifying the offset parameter. #8438
• Fixed a crash when creating a plane with both position and normal on the Z-axis. #8576
• Fixed BoundingSphere.projectTo2D when the bounding sphere’s center is at the origin. #8482

参考链接

1. Camera Controller can go underground,by cesium.
2. Prevent camera from going underground during mouse navigation,by cesium.

我们知道，在使用美国GPS时，需要获得三颗GPS卫星信号，才能够定位自身位置。那么其背后的原理是什么呢？很简单，用数学语言表述，就是通过求解三个球的交点。通常三个球的交点会有两个点，排除位置较高的那个点，剩下的点就是我们空间位置点。

参考链接

1. How Does GPS Work?,by Aryaman Sharda.
2. 三个球的交点,by sinat_27504423.

简介

This guide begins with an introduction called, ‘So what’s plain English?’

The guide then looks at the main ways to make writing clearer.

• Keep your sentences short
• Prefer active verbs
• Use ‘you’ and ‘we’
• Use words that are appropriate for the reader
• Don’t be afraid to give instructions
• Avoid nominalisations
• Use lists where appropriate

The guide then looks at the difficult subject of apologising, and deals with some of the myths that can get in the way of clear communication.

The guide finishes with a summary and a list of words to avoid.

什么是简单英语

First let’s say what plain English isn’t and destroy some of the myths about it.

• It’s not ‘cat sat on the mat’ or ‘Janet and John’ writing. Almost anything - from leaflets and letters to legal documents - can be written in plain English without being patronising or oversimplified.
• It doesn’t mean reducing the length of your message or changing its meaning. Most of the UK’s biggest insurance companies produce policies that explain everything fully in plain English.
• It’s not about banning new words, killing off long words or promoting completely perfect grammar. Nor is it about letting grammar slip.
• It is not an amateur’s method of communication. Most forward-looking senior managers always write in plain English.
  And finally, it is not as easy as we would like to think.

句子尽量短

Most experts would agree that clear writing should have an average sentence length of 15 to 20 words.

使用主动语态

Do you want your letters to sound active or passive - crisp and professional or stuffy and bureaucratic?

合适使用被动语态

There are times of course when it might be appropriate to use a passive.

• To make something less hostile - ‘this bill has not been paid’ (passive) is softer than ‘you have not paid this bill’ (active).
• To avoid taking the blame - ‘a mistake was made’ (passive) rather than ‘we made a mistake’ (active).
• When you don’t know who or what the doer is - ‘the England team has been picked’.
• If it simply sounds better.

使用你们和我们

Try to call the reader ‘you’, even if the reader is only one of many people you are talking about generally. If this feels wrong at first, remember that you wouldn’t use words like ‘the applicant’ and ‘the supplier’ if you were speaking to somebody sitting across a desk from you.

使用适合读者的字词

When you are talking to your reader, say exactly what you mean, using the simplest words that fit. This does not necessarily mean only using simple words - just words that the reader will understand.

At the end of this guide there is a list of a few of the words that we suggest you avoid. But for most words you will have to decide yourself whether they are suitable.

Jargon is a type of language that is only understood by a particular group of people. You can use jargon when writing to people who will understand the terms and phrases. It can be a useful form of shorthand. But try to avoid using specialist jargon on the general public.

So in general, keep to everyday English whenever possible. And again, imagine talking to your reader across a table.

不用担心使用祈使句

Sit!

Brush your teeth.

Please send it to me.

These are all commands - officially called imperatives. They are the fastest and most direct way of giving someone instructions.

However, if we asked a hardened bureaucrat to write these expressions, we would end up with something like the following.

避免使用名词

A nominalisation is a type of abstract noun. (Is that plain English?) In other words, it is the name of something that isn’t a physical object, such as a process, technique or emotion.

Nominalisations are formed from verbs.

参考链接

1. How to write in plain English,by plainenglish.
2. 英语中表达并列，and前加不加逗号？,by zhihu.
3. 英文中关于逗号使用方法,by 桃子爱不完.
4. 状语,by wikipedia.
5. 英语动名词作定语的用法形式有哪些,by 大山教育.
6. 考研英语：英语语法中只有三大从句,by yanzhaowang.
7. 过去分词在句子中做状语的用法总结,by 古月月.
8. 现在分词在句子中作状语的用法,by 古月月.
9. 副词修饰动词时在英语句子中不同的位置,by yufa.
10. 定语,by wikipedia.
11. English learning,by 一飞同学.
12. 表语,by wikipedia.

拖放是网页中一种很常见的交互手段。下面简单介绍使用js实现拖放功能的方法。

拖放流程

拖放元素的流程如下：

选中元素—>拖动元素—>释放元素

下面介绍上述拖放元素流程的具体实现方法。

选中元素

在HTML5标准中，为了使元素可拖动，把draggable属性设置为true。文本、图片和链接是默认可以拖放的，它们的draggable属性自动被设置成了true。图片和链接按住鼠标左键选中，就可以拖放。文本只有在被选中的情况下才能拖放。如果显示设置文本的draggable属性为true，按住鼠标左键也可以直接拖放。

draggable属性：设置元素是否可拖动。语法：

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<element draggable="true | false | auto" >

其中：

• true: 可以拖动
• false: 禁止拖动
• auto: 跟随浏览器定义是否可以拖动

拖动元素

每一个可拖动的元素，在拖动过程中，都会经历三个过程，拖动开始–>拖动过程中–> 拖动结束。

释放

到达目的地之后，释放元素事件

DataTransfer对象

与拖放操作所触发的事件同时派发的对象是DragEvent，它派生于MouseEvent，具有Event与MouseEvent对象的所有功能，并增加了dataTransfer属性。该属性用于保存拖放的数据和交互信息，返回DataTransfer对象。

DataTransfer对象常用的属性和方法如下：

浏览器文件拖拽示例

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document.addEventListener("dragenter",function(e) {
    e.preventDefault();
    e.stopPropagation();
},false);

document.addEventListener("dragover",function(e) {
    e.preventDefault();
    e.stopPropagation();
},false);

document.addEventListener("dragleave",function(e) {
    e.preventDefault();
    e.stopPropagation();
},false);

document.addEventListener("drop",function(e) {
    e.preventDefault();
    e.stopPropagation();

    var  df = e.dataTransfer;
    var dropFiles=[];

    if (df.items !==undefined){
        for(var i=0;i<df.items.length;i++){
            var item= df.items[i];
            if(item.kind==="file" && item.getAsEntry().isFile){
                var file =item.getAsFile();
                dropFiles.push(file);
            }
        }
    }
},false);

参考链接

1. js控制文件拖拽，获取拖拽内容。,by segmentfault.
2. HTML5原生拖拽/拖放 Drag & Drop 详解,by weiqinl.
3. 原生JS快速实现拖放（drag and drop）效果,by MudOnTire.

Simulink在建立系统模型方面非常的便捷，利用其提供的各种已封装好的组件，可以很快地构建各种模型，如飞机、导弹、诱饵弹等。但是在将导弹、诱饵弹装配到飞机上时就比较复杂了。例如，在飞机发射导弹时，如何将飞机的速度、位姿状态传递给导弹模型就是一个难题。为解决该难题，Simulink必须能够在线修改模型的参数。幸运的是，尽管比较艰难，通过一些特殊的技巧，Simulink还是能够实现在线修改模型参数的。具体的解决方案如下：

• 模型实例化问题。以飞机携带多枚导弹为例，因为飞机携带导弹数量有限，可以直接生成多个导弹模块。如果数量实在太多，可以考虑for each subsystem。

• 在线修改模型参数问题。利用Simulink的s函数，在Update函数中使用set_param函数修改模型参数。

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function Update(block)
    decoyID=block.DialogPrm(1).Data; 
    decoyName=sprintf('%s%d','JetFlighterWithDecoy/Decoys/Decoy',decoyID);

    % 脉冲信号上升沿触发，设置模型参数
    if(block.InputPort(4).Data==1 && block.Dwork(1).Data==0)
        fligherSpeed=block.InputPort(2).Data;
        decoySpeed=[fligherSpeed(1) fligherSpeed(2) fligherSpeed(3)-30];
        dcm=block.InputPort(3).Data;
        docoySpeedInFlatEarth=inv(dcm)*decoySpeed';
        v0=join(['[' string(docoySpeedInFlatEarth') ']']);
        pos0=join(['[' string(block.InputPort(1).Data') ']']);
        set_param(decoyName,'ParameterArgumentValues',struct('decoySpeed',char(v0),'decoyPos',char(pos0)));
        block.Dwork(1).Data = 1;%使能信号
end

参考链接

1. Simulink模块参数在线修改方法的研究,by 郑志波.
2. Why do I get an error when specifying a Simscape component parameter with same name as built-in Simulink parameter?,by mathworks.
3. Parameterize Instances of a Reusable Referenced Model,by mathworks.
4. find_system,by mathworks.

“有图有真相”、“一图抵千言”，这些俗语充分体现了大数据时代图的重要性。与枯燥的数据相比，丰富多样的图形更能揭示数据背后的规律，更受普罗大众的欢迎。因此有必要了解和熟悉一些常用的图，以便根据数据选择合适的图形表示。

弦图 (Chord Diagram)

描述

弦图 (Chord Diagram) 可以显示不同实体之间的相互关系和彼此共享的一些共通之处，因此这种图表非常适合用来比较数据集或不同数据组之间的相似性。

节点围绕着圆周分布，点与点之间以弧线或贝塞尔曲线彼此连接以显示当中关系，然后再给每个连接分配数值（通过每个圆弧的大小比例表示）。此外，也可以用颜色将数据分成不同类别，有助于进行比较和区分。

弦图的缺点是过于混乱，尤其是当要显示太多连接的时候。

功能

• 比较
• 关系

旭日图

描述

也称为「多层饼形图」或「径向树图」。

这种图表通过一系列的圆环显示层次结构，再按不同类别节点进行切割。每个圆环代表层次结构中的一个级别，中心圆表示根节点，层次结构从这点往外推移。

之后圆环会按照其与原属切片的层次关系再被分割，分割角度可以是均等平分，或者与某个数值成比例。

我们也可以用不同颜色突出显示层次分组或特定类别。

功能

• 层次结构
• 部分对整体

参考链接

1.数据可视化工具目录,by datavizcatalogue.