Java GeoTools：如何在形状文件中查找点到最近多边形的距离

Question

所以我有一个包含一堆多边形的 shp 文件。在这种情况下，多边形是一片内陆水域（如湖泊之类的东西）。

我的系统正在跟踪一个移动的物体，所以为了确定这个物体是什么，我想看看这个物体​​是在水中还是在陆地上，以及它离最近的海岸有多远（是的，如果它在或出水）。我会不时从对象中抽取一个样本点并对其进行测试。

系统是Java编写的，我已经导入了GeoTools snapshot 17。但是如果其他utils更容易使用，没有要求使用这个。

要测试该点是否在水中（即在多边形内），此方法有效：

private void findPolygonsForPoint(Coordinate point) {
    Filter filter = null;
    SimpleFeatureIterator iterator = null;
    try {
        filter = CQL.toFilter("CONTAINS(the_geom, POINT(" + point.x + " " + point.y + "))");

        SimpleFeatureCollection collection = source.getFeatures(filter);
        if(collection.size() < 1) {
            System.out.println(coordinate2String(point) + " is NOT in a polygon");
        } else {
            System.out.println(coordinate2String(point) + " IS in a polygon");
            insidePolygon++;
            iterator = collection.features();

            while(iterator.hasNext()) {
                SimpleFeature feature = iterator.next();
                //find nearest edge of the polygon
            }
        }
    } catch(CQLException e) {
        aLog.error("", e);
    } catch(IOException e) {
        aLog.error("", e);
    } finally {
        if(iterator != null) {
            iterator.close();
        }
    }
}

现在问题：

1) 如果点不在多边形中，我如何在源中找到最近的多边形（作为 SimpleFeatureSource）？

2) 如何找到距离最近的多边形边缘的距离？

任何帮助将不胜感激！尤其是代码示例——我对数学和几何有点生疏了。

谢谢。

Answer 1

最简单的答案是使用SpatialIndexFeatureCollection 为您完成繁重的工作，它会找到最近的多边形，然后您可以检查您是在里面还是在外面。

这样一个简单的类：

public class NearestPolygon {
  private static FilterFactory2 ff = CommonFactoryFinder.getFilterFactory2();
  private static GeometryFactory gf = new GeometryFactory();
  private SpatialIndexFeatureCollection index;
  private SimpleFeature lastMatched;

  public NearestPolygon(SimpleFeatureCollection features) {

    index = new SpatialIndexFeatureCollection(features.getSchema());
    index.addAll(features);
  }



  public Point findNearestPolygon(Point p) {
    final double MAX_SEARCH_DISTANCE = index.getBounds().getSpan(0);
    Coordinate coordinate = p.getCoordinate();
    ReferencedEnvelope search = new ReferencedEnvelope(new Envelope(coordinate),
        index.getSchema().getCoordinateReferenceSystem());
    search.expandBy(MAX_SEARCH_DISTANCE);
    BBOX bbox = ff.bbox(ff.property(index.getSchema().getGeometryDescriptor().getName()), (BoundingBox) search);
    SimpleFeatureCollection candidates = index.subCollection(bbox);

    double minDist = MAX_SEARCH_DISTANCE + 1.0e-6;
    Coordinate minDistPoint = null;
    try (SimpleFeatureIterator itr = candidates.features()) {
      while (itr.hasNext()) {

        SimpleFeature feature = itr.next();
        LocationIndexedLine line = new LocationIndexedLine(((MultiPolygon) feature.getDefaultGeometry()).getBoundary());
        LinearLocation here = line.project(coordinate);
        Coordinate point = line.extractPoint(here);
        double dist = point.distance(coordinate);
        if (dist < minDist) {
          minDist = dist;
          minDistPoint = point;
          lastMatched = feature;
        }
      }
    }
    Point ret = null;
    if (minDistPoint == null) {
      ret = gf.createPoint((Coordinate) null);
    } else {
      ret = gf.createPoint(minDistPoint);
    }
    return ret;
  }

  public SimpleFeature getLastMatched() {
    return lastMatched;
  }
}

可以使用如下代码调用：

  public static void main(String[] args) throws IOException {
    String lakes = "/data/natural_earth/10m_physical/ne_10m_lakes.shp";
    HashMap<String, Object> params = new HashMap<>();
    params.put("url", DataUtilities.fileToURL(new File(lakes)));
    DataStore ds = DataStoreFinder.getDataStore(params);

    String name = ds.getTypeNames()[0];
    SimpleFeatureSource source = ds.getFeatureSource(name);
    SimpleFeatureCollection features = source.getFeatures();
    NearestPolygon polyFinder = new NearestPolygon(features);
    for (int i = 0; i < 100; i++) {
      Point p = GenerateRandomData.createRandomPoint();
      Point pointOnLine = polyFinder.findNearestPolygon(p);
      if (!pointOnLine.isEmpty()) {
        System.out.println(i+" At " + pointOnLine + " is closest to " + p);
        SimpleFeature lastMatched2 = polyFinder.getLastMatched();
        String attribute = (String) lastMatched2.getAttribute("name");
        if(attribute.isEmpty()) {
          attribute = (String) lastMatched2.getAttribute("note");
        }
        if (((Geometry) (lastMatched2.getDefaultGeometry())).contains(p)) {
          System.out.println("is in lake " + attribute);
        } else {
          System.out.println("nearest lake is " + attribute);
        }

      }
    }
  }