GeoTools坐标转换（投影转换和仿射变换）

GeoTools是在java下的gis开源软件，以下介绍坐标转换的两种方法：投影转换和仿射变换

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• 投影转换

这里以xian80经纬度坐标转xian80，3度分带 111中央经线平面坐标为例

转换函数如下：

         Point pointXian80 = projectTransform(lon, lat, "EPSG:4610", "EPSG:2382");

     /**
      * 投影转换， lon=经度，lat=纬度，ESPG格式（例）：EPSG:4610
      */
     public static Point projectTransform(double lon, double lat,
             String epsgSource, String epsgTarget) throws FactoryException,
             MismatchedDimensionException, TransformException {
         // 原始坐标点
         // PS:通常逻辑上理解经度应该是横坐标x，纬度是y，可是这里经度要填到y，纬度x，否则会报错
         Point sourcePoint = JtsHelper.createPoint(lat, lon);

         // 定义转换前和转换后的投影，可以用ESPG或者wkt
         // "PROJCS[\"Xian_1980_3_Degree_GK_CM_111E\",GEOGCS[\"GCS_Xian_1980\",DATUM[\"D_Xian_1980\",SPHEROID[\"Xian_1980\",6378140.0,298.257]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Gauss_Kruger\"],PARAMETER[\"False_Easting\",500000.0],PARAMETER[\"False_Northing\",0.0],PARAMETER[\"Central_Meridian\",111.0],PARAMETER[\"Scale_Factor\",1.0],PARAMETER[\"Latitude_Of_Origin\",0.0],UNIT[\"Meter\",1.0]]";
         // CoordinateReferenceSystem mercatroCRS = CRS.parseWKT(strWKTMercator);
         CoordinateReferenceSystem crsSource = CRS.decode(epsgSource);
         CoordinateReferenceSystem crsTarget = CRS.decode(epsgTarget);
         // 投影转换
         MathTransform transform = CRS.findMathTransform(crsSource, crsTarget);
         Point pointTarget = (Point) JTS.transform(sourcePoint, transform);

         return pointTarget;
     }

关于定义坐标系的说明，GeoTools中定义坐标系有两种方法，一是坐标系的wkt，二是ESPG
坐标系的wkt可以从arcgis的prj文件中过去，用记事本打开prj文件，里面的内容就是该坐标系的wkt格式内容，例如：PROJCS[\"Xian_1980_3_Degree_GK_CM_111E\",GEOGCS[\"GCS_Xian_1980\",DATUM[\"D_Xian_1980\",SPHEROID[\"Xian_1980\",6378140.0,298.257]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Gauss_Kruger\"],PARAMETER[\"False_Easting\",500000.0],PARAMETER[\"False_Northing\",0.0],PARAMETER[\"Central_Meridian\",111.0],PARAMETER[\"Scale_Factor\",1.0],PARAMETER[\"Latitude_Of_Origin\",0.0],UNIT[\"Meter\",1.0]]

获取到wkt后，可以通过 CoordinateReferenceSystem mercatroCRS = CRS.parseWKT(strWKTMercator); 获取到坐标系对象

另一种方法是ESPG，意思是每一个坐标系都有一个ESPG标准的号码，查询坐标系的ESPG可通过以下网站 http://spatialreference.org/

PS：当转换的两种坐标系的datum不同，会报错Bursa-Wolf parameters，暂时未解决

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• 仿射变换

代码如下：

首先是输入三组参考点，前三个是转换前，后三个是转换后

最后结果是pointReuslt

         // 参考点坐标
         Coordinate s1 = new Coordinate(429275.549, 2801455.153);
         Coordinate s2 = new Coordinate(428110.626, 2792148.620);
         Coordinate s3 = new Coordinate(428966.479, 2800016.622);

         Coordinate t1 = new Coordinate(4628.339, 801349.338);
         Coordinate t2 = new Coordinate(3515.906, 792036.308);
         Coordinate t3 = new Coordinate(4327.381, 799909.069);
         // 建立仿射变换对象
         AffineTransformationBuilder afb = new AffineTransformationBuilder(s1,
                 s2, s3, t1, t2, t3);
         AffineTransformation atf = afb.getTransformation();

         Point pointReuslt = JtsHelper.createPoint(x,y);

         // 坐标转换
         pointReuslt.apply(atf);