有没有做GIS开发的大佬，相知道LineString的自相交和面的自相交是怎么验证的

Question

查遍了JTS的Api,一直没找到方法，两个个几何对象的倒有，但一个几何对象的没有，另外，MULTIPOLYGON该如何打散成多个POLYGON的

Answer 1

该回答引用ChatGPT3.5，结果代码方法已验证可行
对于LineString和Polygon的自相交检测，JTS（Java Topology Suite）提供了相应的方法。

1. LineString自相交检测：
   使用LineIntersector类来检测LineString是否自相交。你可以使用LineIntersector的computeIntersections()方法来计算交点，并检查交点的数量。如果有交点，则表明LineString自相交。

   import com.vividsolutions.jts.geom.Coordinate;
   import com.vividsolutions.jts.geom.Geometry;
   import com.vividsolutions.jts.geom.LineString;
   import com.vividsolutions.jts.geom.PrecisionModel;
   import com.vividsolutions.jts.geom.TopologyException;
   import com.vividsolutions.jts.geom.impl.PackedCoordinateSequenceFactory;
   import com.vividsolutions.jts.geom.util.LineStringExtracter;
   import com.vividsolutions.jts.operation.linemerge.LineMerger;
   import com.vividsolutions.jts.precision.GeometryPrecisionReducer;
   import com.vividsolutions.jts.precision.MinimumClearance;
   import com.vividsolutions.jts.precision.MinimumClearanceFinder;
   import com.vividsolutions.jts.precision.SimpleGeometryPrecisionReducer;
   import com.vividsolutions.jts.util.GeometricShapeFactory;
   import com.vividsolutions.jts.util.Stopwatch;
   
   public class LineStringSelfIntersect {
       public static boolean isSelfIntersect(LineString line) {
           LineIntersector lineIntersector = new RobustLineIntersector();
           Coordinate[] coordinates = line.getCoordinates();
           for (int i = 0; i < coordinates.length - 1; i++) {
               for (int j = i + 1; j < coordinates.length - 1; j++) {
                   lineIntersector.computeIntersection(coordinates[i], coordinates[i + 1], coordinates[j], coordinates[j + 1]);
                   if (lineIntersector.hasIntersection()) {
                       return true;
                   }
               }
           }
           return false;
       }
   }
   

2. Polygon自相交检测：
   对于Polygon自相交的检测，你可以先将Polygon转换为一个LineString，然后使用上述的方法来检测LineString是否自相交。如果是自相交的，说明Polygon也自相交。

   import com.vividsolutions.jts.geom.Geometry;
   import com.vividsolutions.jts.geom.Polygon;
   import com.vividsolutions.jts.operation.polygonize.Polygonizer;
   
   public class PolygonSelfIntersect {
       public static boolean isSelfIntersect(Polygon polygon) {
           Geometry boundary = polygon.getBoundary(); // Get the boundary as LineString
           return LineStringSelfIntersect.isSelfIntersect(boundary);
       }
   }
   

3. MULTIPOLYGON打散成多个POLYGON：
   对于MULTIPOLYGON，你可以使用GeometryCollection类来打散成多个Polygon，然后遍历处理每个Polygon。

   import com.vividsolutions.jts.geom.Geometry;
   import com.vividsolutions.jts.geom.GeometryCollection;
   import com.vividsolutions.jts.geom.Polygon;
   
   public class MultiPolygonToPolygons {
       public static Polygon[] explodeMultiPolygon(MultiPolygon multiPolygon) {
           GeometryCollection geometryCollection = (GeometryCollection) multiPolygon;
           int numGeometries = geometryCollection.getNumGeometries();
           Polygon[] polygons = new Polygon[numGeometries];
           for (int i = 0; i < numGeometries; i++) {
               Geometry geometry = geometryCollection.getGeometryN(i);
               if (geometry instanceof Polygon) {
                   polygons[i] = (Polygon) geometry;
               }
           }
           return polygons;
       }
   }
   

这些方法可以帮助你验证LineString和Polygon的自相交，并将MULTIPOLYGON打散成多个POLYGON。