jts 将单个多边形转换为多边形

Question

大家好，我正在使用带有 geotools 快照 21 的 JTS 1.15：

我编写了一个以多边形集合作为输入参数的方法，输出方法是多多边形几何体。这工作正常，无一例外：我还有一个联合标志，如果重叠或接触，它将联合我的多边形。如果现在所有多边形都重叠，则只会返回一个多边形。但是之后就会出现ClassCastException。

无法将单个多边形转换为多边形

有没有简单的方法可以将单个多边形转换为多边形？我找不到几何 jts uml 图，但我发现了 Polygons 使用 Polygonal 接口扩展了 Geometry class Multipolygon 扩展了 GeometryCollection，它扩展了 Geometry 并且还具有 Polygonal 接口。

在JTS Geometry Jacadoc中提到了以下内容：叠加方法

The overlay methods return the most specific class possible to represent the result. If the result is homogeneous, a Point, LineString, or Polygon will be returned if the result contains a single element; otherwise, a MultiPoint, MultiLineString, or MultiPolygon will be returned. If the result is heterogeneous a GeometryCollection will be returned.

我写了一个简单的字符串操纵器方法来更改我的 wkt 字符串，但是还有其他方法可以实现这个目标吗？

这是我的方法

public static MultiPolygon createSPMultiPolygon(Collection<Polygon> polygons, boolean dissolveResult) {


    // if emty collection is returned
    if (polygons.size() == 0){
        //emty collection returns emty MultiPolygon

        GeometryFactory geomFactory = new GeometryFactory();
        MultiPolygon fail = geomFactory.createMultiPolygon();

        return fail;
    }

    //it will be assumed that all polygons have the same epsg code

    int epsgCode = polygons.iterator().next().getSRID();
    prec = new PrecisionModel(1000000)
    //creates the factory object
    GeometryFactory geomFactory = new GeometryFactory(prec, epsgCode);

    MultiPolygon result = null;


    // main task

    result = (MultiPolygon) geomFactory.buildGeometry(polygons);


        //mergedOptions
        if (dissolveResult) {

            try {
                result = (MultiPolygon) result.union();
                // there will be an exception if result or merge is a single polygon that polygon cant be cast to Multipolygon
            } catch (ClassCastException e) {

                // DO SOMETHING ELSE
            }

        }

    }

我正在使用以下 Maven 包：

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <geotools.version>21-SNAPSHOT</geotools.version>
</properties>
<dependencies>
<dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.11</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.geotools</groupId>
  <artifactId>gt-geometry</artifactId>
  <version>${geotools.version}</version>
</dependency>
<dependency>
  <groupId>org.geotools</groupId>
  <artifactId>gt-epsg-hsql</artifactId>
  <version>${geotools.version}</version>
</dependency>
<dependency>
  <groupId>org.geotools</groupId>
  <artifactId>gt-epsg-wkt </artifactId>
  <version>${geotools.version}</version>
</dependency>

我正在使用以下示例数据和辅助函数：

    String touches1_wkt = "POLYGON ((7.896407750956972 49.73405361813658, 8.14886306623246 49.73405361813658, 8.14886306623246 49.73405361813658, 8.14886306623246 49.46768344296402, 7.902371262341433 49.46569560583586, 7.896407750956972 49.73405361813658))";
    String touches2_wkt = "POLYGON ((8.14886306623246 49.61478339044737, 8.39137919586718 49.616771227575526, 8.39137919586718 49.616771227575526, 8.399330544379795 49.35835240091558, 8.14886306623246 49.35835240091558, 8.14886306623246 49.46768344296402, 8.14886306623246 49.61478339044737))";


    Polygon touch1 = (Polygon) createSPGeom(touches1_wkt, 4326);
    Polygon touch2 = (Polygon) createSPGeom(touches2_wkt, 4326);

    Collection<Polygon> polyCollection = new ArrayList<>();
    polyCollection.add(touch1);
    polyCollection.add(touch2);

    MultiPolygon multi = createSPMultiPolygon(polyCollection, true);

使用以下帮助方法进行 wkt 阅读：

     public static Geometry createSPGeom(String wktString, Integer epsgCode){

    Geometry returnedGeom =null;
    prec = new PrecisionModel(1000000);

    GeometryFactory geomFactory = new GeometryFactory(prec, epsgCode);
    WKTReader wktReader = new WKTReader(geomFactory);

    try {
        returnedGeom = wktReader.read(wktString);
    } catch (ParseException e) {
        // if wktString is invalid, an emty point geometry is used
        returnedGeom = geomFactory.createPoint();
    }

    return returnedGeom;
}

提前感谢您的帮助

Answer 1

您的 ClassCastException 似乎可以通过检查对 union() returns 的调用是否为多边形来处理。如果是这样，您可以使用仅包含一个多边形的数组调用 GeometryFactorys 的 createMultiPolygon。[1]

https://github.com/locationtech/jts/blob/master/modules/core/src/main/java/org/locationtech/jts/geom/GeometryFactory.java#L326

Answer 2

正如GeoMesaJim所说，这是一个简单的问题，只需将多边形提升为多多边形即可。

GeometryFactory gf = new GeometryFactory();
MultiPolygon mPoly;
if (p instanceOf Polygon){
  Polygon[] polys = new Polygon[1];
  polys[0] = p;
  mPoly = gf.createMultiPolygon(polys);
} else {
   mPoly = p;
}
System.out.println(mPoly);

jts 将单个多边形转换为多边形

jts convert single polygon to multipolygon

geometry

casting

jts

geotools