本文主要介绍使用ArcGIS JS API 4.14和eCharts 4.7.0来实现在地图上绘制散点图的实现步骤,包括二维和三维。
概述
上一篇文章中我们介绍了如何使用ArcGIS JS API和eCharts结合,在二维和三维场景下绘制迁徙图。这篇文章我们来介绍下如何在二维和三维场景下绘制散点图,其实散点图跟迁徙图一样,它的绘制也跟地理坐标系有关,所以实现思路跟迁徙图的绘制是一样的,我们来看下最终效果:
实现思路
迁徙图、散点图这种图表跟地理坐标关系紧密,所以仅仅通过二维普通图表绘制的方式是无法实现这类图表绘制的,所以就需要我们来扩展eCharts的相关功能,使其能够够结合最新版的ArcGIS JS API来完成地图上这类图表的绘制,eCharts官网也提供了相应的扩展插件,但这种插件并不能很好地支持我们ArcGIS JS API的高版本,所以我们在这篇文章里直接扩展了一个图层类,下面是具体的实现思路:
实现ArcGIS JS API和eCharts的结合,最最关键的是要实现两个插件库里的坐标系转换,这是重点,只要搞清楚了这一点,我们完全可以脱离地图API库的束缚,理论上可以实现eCharts跟任意地图库的结合。在此处转换坐标时我们使用了eCharts提供的registerCoordinateSystem方法,通过这个方法我们注册了一个名为”arcgis”的坐标系,里面对eCharts中的dataToPoint、pointToData等方法进行了重写,然后将这些所有内容封装为了一个EchartsLayer图层类。至于这个文件的源码,文章结尾会提供,接下来我们看一下具体的实现步骤。
实现步骤
1、本文所用的demo同样是基于React框架搭建的,所以我们首先基于React框架搭建一个初始化项目,然后改写src目录下的App.js这个主文件,实例化出一张二维地图,这中间用到了esri-loader插件,具体的实现过程可查看我的这篇文章【【番外】 React中使用ArcGIS JS API 4.14开发】,里面有具体的实现步骤。
2、通过上述操作实例化完一张二维地图后,我们接下来就要进行散点图的绘制操作了,在开始之前我们需要一些数据,首先是散点图中所要用到的各个城市坐标,我在此处将它们单独抽出来作为一个js文件,源文件如下:
1 | let geoCoordMap = { |
除了上述的城市坐标之外,我们还需要一份跟城市坐标相对应的权重数据,用来表示某个指标在各个城市的值,同样的是一份单独的js文件,源代码如下:
1 | let dataValue = [ |
3、完成了以上操作之后,我们接下来就要进行散点图的配置信息初始化,在此处其实就是实例化series这个属性,代码如下:
1 | //初始化图表参数 |
上述代码中用到了数据转换这个方法,代码如下:
1 | _convertData=(data) => { |
4、图表信息初始化之后,接下来监听地图的绘制完成事件,然后调用绘制图表函数来进行图表的绘制,代码如下:
1 | view.when(function() { |
1 | //绘制图表 |
5、通过以上操作过程就实现了散点图的绘制,如果需要绘制三维场景下的散点图,只需要将mapview更改为sceneview即可。
总结
本文在上一篇文章的基础之上跟大家介绍了一下使用ArcGIS JS API和eCharts来绘制二维和三维场景下的散点图的过程,为了便于代码组织,这篇文章中的代码是在src目录下新建了一个scatterDiagram的组件,如果大家觉得麻烦,可将此组件中的代码直接拷贝到App.js文件里进行学习和参考,中间没有任何问题。
附:
散点图绘制全部源码:
1 | import React,{Component} from 'react'; |
EchartsLayer.min.js源码:
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