经纬度坐标和投影坐标的转换

清疚 2022-08-18 08:37 298阅读 0赞

昨天，有朋友要我帮忙看看一个将经纬度坐标转换成墨卡托投影（墨卡托投影有很多变种，我也不知道他说的是哪一种）的程序，他说转换以后的坐标精度太差。当时，他的程序没怎么看懂，然后研究了一下Geotools，自己写了一个转换小程序，很简单的几行代码！

Geotools是Java语言编写的开源GIS工具包。该项目已有十多年历史，生命力旺盛，代码非常丰富，包含多个开源GIS项目，并且基于标准的GIS接口。Geotools主要提供各种GIS算法，各种数据格式的读写和显示。由于Geotools库依赖比较复杂，所以在Eclipse中我采用Maven进行建构。对于在Eclipse下怎么使用Maven，请自己百度之。貌似最新的Eclipse是直接集成Maven插件的不需要自己单独安装了。虽说Eclipse不需要安装Maven插件了，可以使用Eclipse自带的Eclipse Maven插件，但是还是建议自己安装一个最新的Maven二进制包。

在Eclipse新建Maven工程，添加库和依赖：

这里主要添加的是要下载Geotools的库：

<repositories>
        <repository>
            <id>maven2-repository.dev.java.net</id>
            <name>Java.net repository</name>
            <url>http://download.java.net/maven/2</url>
        </repository>
        <repository>
            <id>osgeo</id>
            <name>Open Source Geospatial Foundation Repository</name>    <url>http://download.osgeo.org/webdav/geotools/</url>
        </repository>
      </repositories>

以及用到的Geotools库：

<dependencies>
        <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version>4.12</version>
          <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.geotools</groupId>
            <artifactId>gt-referencing</artifactId>
            <version>${geotools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.geotools</groupId>
            <artifactId>gt-epsg-wkt</artifactId>
            <version>${geotools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.geotools</groupId>
            <artifactId>gt-api</artifactId>
            <version>${geotools.version}</version>
        </dependency>
        <dependency>
            <groupId>com.vividsolutions</groupId>
            <artifactId>jts</artifactId>
            <version>1.13</version>
        </dependency>
      </dependencies>

最后的pom.xml文件如下：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
      <modelVersion>4.0.0</modelVersion>
    
      <groupId>cn.tzy</groupId>
      <artifactId>geotools</artifactId>
      <version>0.0.1-SNAPSHOT</version>
      <packaging>jar</packaging>
    
      <name>geotools</name>
      <url>http://maven.apache.org</url>
    
      <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <geotools.version>14.1</geotools.version>
      </properties>
    
      <repositories>
        <repository>
            <id>maven2-repository.dev.java.net</id>
            <name>Java.net repository</name>
            <url>http://download.java.net/maven/2</url>
        </repository>
        <repository>
            <id>osgeo</id>
            <name>Open Source Geospatial Foundation Repository</name>    <url>http://download.osgeo.org/webdav/geotools/</url>
        </repository>
      </repositories>
    
      <dependencies>
        <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version>4.12</version>
          <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.geotools</groupId>
            <artifactId>gt-referencing</artifactId>
            <version>${geotools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.geotools</groupId>
            <artifactId>gt-epsg-wkt</artifactId>
            <version>${geotools.version}</version>
        </dependency>
        <dependency>
            <groupId>org.geotools</groupId>
            <artifactId>gt-api</artifactId>
            <version>${geotools.version}</version>
        </dependency>
        <dependency>
            <groupId>com.vividsolutions</groupId>
            <artifactId>jts</artifactId>
            <version>1.13</version>
        </dependency>
      </dependencies>
    </project>

下面开始写程序：

package cn.tzy.geotools;
    
    import org.geotools.geometry.jts.JTS;
    import org.geotools.referencing.CRS;
    import org.geotools.referencing.crs.DefaultGeographicCRS;
    import org.opengis.geometry.MismatchedDimensionException;
    import org.opengis.referencing.FactoryException;
    import org.opengis.referencing.crs.CoordinateReferenceSystem;
    import org.opengis.referencing.operation.MathTransform;
    import org.opengis.referencing.operation.TransformException;
    
    import com.vividsolutions.jts.geom.Coordinate;
    import com.vividsolutions.jts.geom.GeometryFactory;
    import com.vividsolutions.jts.geom.Point;
    
    /** * Hello world! * */
    public class CoordConverter { 
        public static double[] convert(double lon, double lat) 
                throws FactoryException, MismatchedDimensionException, TransformException {
            // 传入原始的经纬度坐标
            Coordinate sourceCoord = new Coordinate(lon, lat);
            GeometryFactory geoFactory = new GeometryFactory();
            Point sourcePoint = geoFactory.createPoint(sourceCoord);
    
            // 这里是以OGC WKT形式定义的是World Mercator投影，网页地图一般使用该投影
            final String strWKTMercator = "PROJCS[\"World_Mercator\","
                    + "GEOGCS[\"GCS_WGS_1984\","
                    + "DATUM[\"WGS_1984\","
                    + "SPHEROID[\"WGS_1984\",6378137,298.257223563]],"
                    + "PRIMEM[\"Greenwich\",0],"
                    + "UNIT[\"Degree\",0.017453292519943295]],"
                    + "PROJECTION[\"Mercator_1SP\"],"
                    + "PARAMETER[\"False_Easting\",0],"
                    + "PARAMETER[\"False_Northing\",0],"
                    + "PARAMETER[\"Central_Meridian\",0],"
                    + "PARAMETER[\"latitude_of_origin\",0],"
                    + "UNIT[\"Meter\",1]]";
            CoordinateReferenceSystem mercatroCRS = CRS.parseWKT(strWKTMercator);
            // 做投影转换，将WCG84坐标转换成世界墨卡托投影转
            MathTransform transform = CRS.findMathTransform(DefaultGeographicCRS.WGS84, mercatroCRS);
            Point targetPoint = (Point) JTS.transform(sourcePoint, transform);
    
            // 返回转换以后的X和Y坐标
            double[] targetCoord = {targetPoint.getX(), targetPoint.getY()};
            return targetCoord;
        }
    
        // 将目标投影坐标系作为参数输入，其实和第一个程序类似，我懒得提取公共部分再抽取函数了
        public static double[] convert(double lon, double lat, String strWKT) 
                throws FactoryException, MismatchedDimensionException, TransformException {
            Coordinate sourceCoord = new Coordinate(lon, lat);
            GeometryFactory geoFactory = new GeometryFactory();
            Point sourcePoint = geoFactory.createPoint(sourceCoord);
    
            CoordinateReferenceSystem mercatroCRS = CRS.parseWKT(strWKT);
            MathTransform transform = CRS.findMathTransform(DefaultGeographicCRS.WGS84, mercatroCRS);
            Point targetPoint = (Point) JTS.transform(sourcePoint, transform);
    
            double[] targetCoord = {targetPoint.getX(), targetPoint.getY()};
            return targetCoord;
        }
    
        // main函数进行验证
        public static void main( String[] args ) throws Exception
        {
            double longitude = 113.926982;
            double latitude = 22.53089;
            double[] coordinate = convert(longitude, latitude);
    
            System.out.println("X: " + coordinate[0] + ", Y: " + coordinate[1]);
        }
    }

程序很简单：CRS.findMathTransform()方法定义转换的坐标系，JTS.transform()进行坐标的转换。

其中第一个方法是我专门写的将WGS84经纬度坐标转成World Mercator投影坐标的函数。第二个函数是对第一个函数的抽象，将要转换到的投影坐标提取出来作为参数，如果想要转换到某种投影坐标系，只需要传递一个该投影坐标系的OGC WKT（Well Known Text）给函数，就可以做转换了。常见投影的WKT表示可以在[http://spatialreference.org/][http_spatialreference.org]进行查询！  
看懂了该程序的朋友，就可以写自己的实现了，上面只是一个简单的Hello World示例程序。

[http_spatialreference.org]: http://spatialreference.org/