目前最新的Nodejs LTS已不再支持Windows7。如需在Windows7上安装Nodejs，需安装12.19.1或之前的版本。
参考链接
- windows安装Node JS及配置,by 兰若惜.
使用Electron和Vuejs创建桌面应用程序的方法
最近遇到一个奇特的需求，要求构建一个评估系统，分为前后端。它的前端是桌面应用程序，后端也是桌面应用程序。前后端之间的通信是通过前端导出一个数据包文件，然后交给后端导入完成的。由于熟悉Nodejs前后端开发，我选择Electron加Vuejs的解决方案。具体的技术选型如下：
- 前端：electron+vuejs+indexedDB+localForage，前端程序需要存储数据，但数据量会比较小，通常使用indexedDB就足够了。
- 后端：electron+vuejs+sqlite3+sequlize，后端程序会汇总前端程序导出的数据包，并做一些统计查询，存储数据量大，读写效率要求高。因此选择sqlite3数据库，可随electron打包到一起安装。
技术简介
Electron简介
Electron（原名为Atom Shell）是GitHub开发的一个开源框架。它允许使用Node.js（作为后端）和Chromium（作为前端）完成桌面GUI应用程序的开发。Electron现已被多个开源Web应用程序用于前端与后端的开发，著名项目包括GitHub的Atom和微软的Visual Studio Code。
一个基础的Electron包含三个文件：package.json（元数据）、main.js（代码）和index.html（图形用户界面）。框架由Electron可执行文件（Windows中为electron.exe、macOS中为electron.app、Linux中为electron）提供。开发者可以自行添加标志、自定义图标、重命名或编辑Electron可执行文件。
vuejs简介
Vue.js是一款流行的JavaScript前端框架，旨在更好地组织与简化Web开发。Vue所关注的核心是MVC模式中的视图层，同时，它也能方便地获取数据更新，并通过组件内部特定的方法实现视图与模型的交互。
Vuejs适合开发单页应用程序。
indexedDB数据库简介
IndexedDB 是一种底层 API，用于在客户端存储大量的结构化数据（也包括文件/二进制大型对象（blobs））。该 API 使用索引实现对数据的高性能搜索。虽然 Web Storage 在存储较少量的数据很有用，但对于存储更大量的结构化数据来说力不从心。而 IndexedDB 提供了这种场景的解决方案。
IndexedDB 是一个事务型数据库系统，类似于基于 SQL 的 RDBMS。 然而，不像 RDBMS 使用固定列表，IndexedDB 是一个基于 JavaScript 的面向对象数据库。IndexedDB 允许您存储和检索用键索引的对象；可以存储结构化克隆算法支持的任何对象。您只需要指定数据库模式，打开与数据库的连接，然后检索和更新一系列事务。
indexedDB的API不够友好，建议使用localForage，支持类Storage API语法的客户端数据存储polyfill，支持回退到Storage和Web SQL
项目构建过程
构建Vuejs项目
使用如下命令构建Vuejs项目脚手架：
1 | npm install -g @vue/cli |
构建Electron项目
在上一节创建Vuejs项目的基础上，使用如下命令为Vuejs项目添加Electron支持，从而生成桌面应用程序：
1 | vue add electron-builder |
构建Sqlite3数据库
使用如下命令为项目添加Sqlite3数据库支持：
1 | npm install sequelize --save --registry https://registry.npm.taobao.org |
构建32位安装程序
使用如下命令构建32位Electron安装程序：
1 | npm run electron:build -- --ia32 |
或者
1 | yarn electron:build --ia32 |
问题备注
Electron构建程序下载依赖包失败
请参考 Electron：运行npm run build构建环境失败解决方案。
Electron makensis构建失败
当遇到如下错误时, 解决方法很简单,打包项目路径不能包含中文路径。
1 | .electron-builder\Cache\nsis\nsis-3.0.3.2\Bin\makensis.exe exited with code ERR_ELECTRON_BUILDER_CANNOT_EXECUTE |
Electron Vuejs显示空白页
请参考Blank screen on builds, but works fine on serve。
支持平台
electron支持macOS、Windows、Linux。在Windows平台，electron仅支持 Windows 7 或更高版本, 旧版操作系统已不再支持(并且无法运行).
参考链接
- Create an Electron application with Vue and Vuetify,by bromix.
- Electron：运行npm run build构建环境失败解决方案,by 请给我一杯冰可乐.
- How to build app for Windows 32bit version?,by nklayman.
- 支持平台,by electronjs.
- Electron应用数据库选型暨indexedDB扫盲,by shenlvmeng.
- LOCALFORAGE,by localforage.
- IndexedDB,by mozilla.
- 浏览器数据库 IndexedDB 入门教程,by ruanyifeng.
- electron集成sqlite3，win10上折腾了2天,by 兴哥.
- Electron笔记,by 小羽信息.
- Blank screen on builds, but works fine on serve,by Vue CLI Plugin Electron Builder.
- Remove menubar from Electron app,by stackoverflow.
Simulink仿真视频教程记录
看了吴菁老师的几个Simulink教学视频，很不错，记录一下。
参考链接
- 使用Simulink和Stateflow快速实现飞行器的设计仿真,by 吴菁.
- 使用Simulink 和Stateflow完成建模、仿真和飞行控制设计,by 吴菁.
- 使用 MATLAB 和 Simulink 让控制系统的开发更轻松,by 吴菁.
- 四旋翼飞行器的建模仿真和控制,by 吴菁.
Cesium支持GLTF动画研究
Cesium在很早之前就支持GLTF模型动画，例如：
1 | var 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：
1 | var czml = [ |
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
- Model Articulations “Number” variable,by cesium.
- glTF 2.0 Quick Reference Guide ,by KhronosGroup.
- glTF,by KhronosGroup.
- Cesium Model Articulations,by cesium.
Cesium去掉黑色星空背景并透明的方法
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：
1 | viewer.scene.skyBox.destroy(); |
参考链接
- Scene Background Transparent,by cesium dev.
Cesium样条插值方法
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
- Cesium专栏-样条插值(平滑路径、飞行动画，源码下载),by GIS之家.
- Cesium的Property机制总结,by vtxf.
- 插值,by wikipedia.
- 样条插值,by wikipedia.
Cesium摄像头进入地面下问题跟踪
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:
1
2
3
4
5
6
7var 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
求三个球交点的方法
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
- How Does GPS Work?,by Aryaman Sharda.
- 三个球的交点,by sinat_27504423.
简单英语写作方法
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
- How to write in plain English,by plainenglish.
- 英语中表达并列，and前加不加逗号？,by zhihu.
- 英文中关于逗号使用方法,by 桃子爱不完.
- 状语,by wikipedia.
- 英语动名词作定语的用法形式有哪些,by 大山教育.
- 考研英语：英语语法中只有三大从句,by yanzhaowang.
- 过去分词在句子中做状语的用法总结,by 古月月.
- 现在分词在句子中作状语的用法,by 古月月.
- 副词修饰动词时在英语句子中不同的位置,by yufa.
- 定语,by wikipedia.
- English learning,by 一飞同学.
- 表语,by wikipedia.