大家好我正在使用JTS 1.15和geotools快照21:
我用Polygon Collection作为输入参数编写了一个方法,输出方法是MultiPolygon Geometry。这是正常工作没有一个例外:我还有一个联合标志,如果重叠或触摸将联合我的多边形。如果现在所有多边形都重叠,则仅返回单个多边形。但是会有一个ClassCastException。
单个多边形无法转换为MultiPolygon
有一种简单的方法可以将单个多边形转换为MultiPolygon吗?我找不到几何jts uml图但是我发现Polygons扩展了Geometry类,接口Polygonal 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
overlay方法返回可能表示结果的最具体的类。如果结果是同质的,如果结果包含单个元素,则返回Point,LineString或Polygon;否则,将返回MultiPoint,MultiLineString或MultiPolygon。如果结果是异构的,则将返回GeometryCollection。
我写了一个简单的字符串操纵器方法来改变我的wkt字符串,但还有另一种方法来实现目标吗?
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帮助函数:
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;
}
在此先感谢您的帮助
正如GeoMesaJim所说,这是一个简单的问题,只需将多边形提升为多边形即可。
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);
看起来你的ClassCastException可以通过检查对union()的调用是否返回Polygon来处理。如果是这样,您可以使用仅包含一个Polygon的数组调用GeometryFactorys的createMultiPolygon。[1]