引言

今天小编碰到个需求，要求通过两个坐标点位向外扩大500米半径，通过这两个500米半径的圆给前端地图提供可画出长方形的四个坐标点

maven引用

        <dependency>
            <groupId>org.osgeo</groupId>
            <artifactId>proj4j</artifactId>
            <version>0.1.0</version>
        </dependency>

代码示例

public class RectangleFromLine {

	/**
	 * 经纬度地理坐标转面坐标
	 * 
	 * @param lat
	 * @param lng
	 * @return
	 */
	public static double[] coordinateTransformation(double lat, double lng) {
		CRSFactory crsFactory = new CRSFactory();
		CoordinateReferenceSystem wgs84 = crsFactory.createFromName("EPSG:4326");
		CoordinateReferenceSystem webMercator = crsFactory.createFromName("EPSG:3857");

		// 创建坐标变换器
		CoordinateTransformFactory ctFactory = new CoordinateTransformFactory();
		CoordinateTransform transform = ctFactory.createTransform(wgs84, webMercator);
		ProjCoordinate srcCoord = new ProjCoordinate(lng, lat);

		// 执行转换
		ProjCoordinate destCoord = new ProjCoordinate();
		transform.transform(srcCoord, destCoord);
		return new double[]{destCoord.x, destCoord.y};
	}

	/**
	 * 面坐标转地理坐标
	 * 
	 * @param x
	 * @param y
	 * @return
	 */
	public static double[] coordinateTransformationReversal(double x, double y) {
		CRSFactory crsFactory = new CRSFactory();
		CoordinateReferenceSystem wgs84 = crsFactory.createFromName("EPSG:4326");
		CoordinateReferenceSystem webMercator = crsFactory.createFromName("EPSG:3857");

		// 创建坐标变换器
		CoordinateTransformFactory ctFactory = new CoordinateTransformFactory();
		CoordinateTransform transform = ctFactory.createTransform(webMercator, wgs84);
		ProjCoordinate srcCoord = new ProjCoordinate(x, y);
		// 执行转换
		ProjCoordinate destCoord = new ProjCoordinate();
		transform.transform(srcCoord, destCoord);
		return new double[]{destCoord.y, destCoord.x};
	}

	/**
	 * 取两圆的最小包围盒(正北方向)
	 * 
	 * @param startLatitude
	 * @param startLongitude
	 * @param endLatitude
	 * @param endLongitude
	 * @param radius
	 * @return
	 */
	public static double[][] calculateRectangleVertices(double startLatitude, double startLongitude, double endLatitude,
			double endLongitude, double radius) {
		double[] p1 = coordinateTransformation(startLatitude, startLongitude);
		double[] p2 = coordinateTransformation(endLatitude, endLongitude);

		double[] leftBottom = new double[]{Math.min(p1[0], p2[0]) - radius, Math.min(p1[1], p2[1]) - radius};
		//面坐标转地理坐标
		double[] leftBottom_1 = coordinateTransformationReversal(leftBottom[0], leftBottom[1]);
		double[] leftTop = new double[]{Math.min(p1[0], p2[0]) - radius, Math.max(p1[1], p2[1]) + radius};
		//面坐标转地理坐标
		double[] leftTop_1 = coordinateTransformationReversal(leftTop[0], leftTop[1]);
		double[] rightTop = new double[]{Math.max(p1[0], p2[0]) + radius, Math.max(p1[1], p2[1]) + radius};
		//面坐标转地理坐标
		double[] rightTop_1 = coordinateTransformationReversal(rightTop[0], rightTop[1]);
		double[] rightBottom = new double[]{Math.max(p1[0], p2[0]) + radius, Math.min(p1[1], p2[1]) - radius};
		//面坐标转地理坐标
		double[] rightBottom_1 = coordinateTransformationReversal(rightBottom[0], rightBottom[1]);
		return new double[][]{leftBottom_1, leftTop_1, rightTop_1, rightBottom_1};
	}

	/**
	 * 取两圆的最小包围盒(轴方向)
	 *
	 * @param startLatitude
	 * @param startLongitude
	 * @param endLatitude
	 * @param endLongitude
	 * @param radius
	 * @return
	 */
	public static double[][] calculateRectangleVertices1(double startLatitude, double startLongitude,
			double endLatitude, double endLongitude, double radius) {
		double[] p1 = coordinateTransformation(startLatitude, startLongitude);
		double[] p2 = coordinateTransformation(endLatitude, endLongitude);

		double minX = Math.min(p1[0], p2[0]) - radius;
		double maxX = Math.max(p1[0], p2[0]) + radius;
		double minY = Math.min(p1[1], p2[1]) - radius;
		double maxY = Math.max(p1[1], p2[1]) + radius;

		// 计算中心点
		double centerX = (minX + maxX) / 2.0;
		double centerY = (minY + maxY) / 2.0;

		// 计算轴方向
		double axisDirection = Math.atan2(maxY - minY, maxX - minX);

		// 计算宽度和高度
		double width = maxX - minX;
		double height = maxY - minY;

		// 计算四个顶点
		double[][] vertices = new double[4][2];
		vertices[0] = calculateVertex(centerX, centerY, width / 2, height / 2, axisDirection, -1, -1);
		vertices[1] = calculateVertex(centerX, centerY, width / 2, height / 2, axisDirection, -1, 1);
		vertices[2] = calculateVertex(centerX, centerY, width / 2, height / 2, axisDirection, 1, 1);
		vertices[3] = calculateVertex(centerX, centerY, width / 2, height / 2, axisDirection, 1, -1);

		// 将顶点从Web Mercator坐标转回地理坐标
		for (int i = 0; i < 4; i++) {
			vertices[i] = coordinateTransformationReversal(vertices[i][0], vertices[i][1]);
		}

		return vertices;
	}

	/**
	 * 计算单个顶点
	 *
	 * @param centerX
	 *            中心点的X坐标
	 * @param centerY
	 *            中心点的Y坐标
	 * @param width
	 *            包围盒的宽度
	 * @param height
	 *            包围盒的高度
	 * @param angle
	 *            轴方向（弧度）
	 * @param dx
	 *            X方向的偏移量（-1或1）
	 * @param dy
	 *            Y方向的偏移量（-1或1）
	 * @return 顶点坐标
	 */
	private static double[] calculateVertex(double centerX, double centerY, double width, double height, double angle,
			int dx, int dy) {
		double x = centerX + dx * width * Math.cos(angle) - dy * height * Math.sin(angle);
		double y = centerY + dx * width * Math.sin(angle) + dy * height * Math.cos(angle);
		return new double[]{x, y};
	}

}