计算不规则地图区域的外接矩形

前言地理知识代码实现Java实现测试（示例）

前言

此方法适合计算我国（中国）领土范围内的不规则地图的外接矩形，不适用于跨正负经度（东西经）的情况（如果后面祖国开疆拓土的话我再来修改:-)）。

地理知识

首先：中国的经纬度范围大约是：纬度3.86至53.55，经度73.66至135.05，不存在跨越正负（东西经南北纬）的问题。其次：由下图可知，在中国地图上任取一个不规则区域，其外接矩形呈现从左向右经度（东经）增加，从下向上纬度（北纬）增加的规则。和我们常用的二维直角坐标系类似。

代码实现

Java实现

结果包装类（计算出的外接矩形的四个点）

@Datapublic class RectanglePosition {//左上角坐标private Position topLeft;//右上角坐标private Position topRight;//左下角坐标private Position bottomLeft;//右下角坐标private Position bottomRight;@Datapublic static class Position {//经度private Double lng;//纬度private Double lat;}}

计算外接矩形

此处入参格式为：118.799774,32.095137;118.799913,32.095085;118.800121,32.094972，即经度1,纬度1;经度2,纬度2;经度3,纬度3;格式

//解析不规则区域外接矩形的四个关键点public static RectanglePosition parseBoundingBox(String pointsStr) {String[] pointStrArr = pointsStr.split(";");Double maxLng = null;Double minLng = null;Double maxLat = null;Double minLat = null;for (String pointStr : pointStrArr) {String[] pointInfo = pointStr.split(",");double lng = Double.parseDouble(pointInfo[0]);double lat = Double.parseDouble(pointInfo[1]);if (maxLng == null) {//初始化为第一个点maxLng = lng;minLng = lng;maxLat = lat;minLat = lat;continue;}if (maxLng < lng) {maxLng = lng;}if (minLng > lng) {minLng = lng;}if (maxLat < lat) {maxLat = lat;}if (minLat > lat) {minLat = lat;}}RectanglePosition result = new RectanglePosition();result.setTopLeft(createPosition(minLng, maxLat));result.setTopRight(createPosition(maxLng, maxLat));result.setBottomRight(createPosition(maxLng, minLat));result.setBottomLeft(createPosition(minLng, minLat));return result;}private static RectanglePosition.Position createPosition(Double lng, Double lat) {RectanglePosition.Position position = new RectanglePosition.Position();position.setLng(lng);position.setLat(lat);return position;}

测试（示例）

玄武区地图

测试代码

此处以南京市玄武区为例，pointStr为玄武区的边缘坐标点集合（边缘点集合可以通过地图厂商提供的接口获取，这里用的是高德地图行政区查询API）。

public static void main(String[] args) {String pointStr = 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position = parseBoundingBox(pointStr);System.out.println(JSONUtil.toJsonPrettyStr(position));}

计算结果

{"bottomLeft": {"lng": 118.783824,"lat": 32.014837},"bottomRight": {"lng": 118.908338,"lat": 32.014837},"topRight": {"lng": 118.908338,"lat": 32.106133},"topLeft": {"lng": 118.783824,"lat": 32.106133}}

将结果绘制到地图上（绘制方法，参见：百度JSSDK覆盖物绘制）

完结散花~~~