Java GeoTools:如何在形状文件中查找从点到最近的多边形的距离 [英] Java GeoTools: how to find distance from a point to closest polygon in shape file

问题描述

所以我有一个shp文件，其中包含一堆多边形.在这种情况下，多边形是内陆水体(例如湖泊和类似东西).

So I have a shp-file containing a bunch of polygons. In this case, a polygon is a body of in-land water (like lakes and that kind of stuff).

我的系统正在跟踪移动中的物体，因此，为了确定该物体是什么，我想查看该物体是在水中还是在陆地上以及它距NEAREST海岸有多远(是的，如果它在水中，或没有水).我会不时从对象中取样一个点并进行测试.

My system is tracking a moving object, so in order to determine what this object is, I would like to see if this object is in water or on land AND how far it is to NEAREST shore (yes, both if it's in or out of water). I will take a sample point from the object once in a while and test it.

系统是用Java编写的，并且我已经导入了GeoTools快照17.但是，如果其他实用程序更易于使用，则没有使用它的要求.

The system is written in Java, and I have imported GeoTools snapshot 17. But if other utils is easier to use, there is no requirements to use this.

要测试该点是否在水中(即在多边形内部)，可以使用以下方法:

To test if the point is IN water (that is, inside a polygon), this methods works:

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();
        }
    }
}

现在是问题:

1)如果该点不在多边形中，如何在源中找到最近的多边形(即SimpleFeatureSource)?

1) If the point is NOT in a polygon, how do I find the nearest polygon in the source (being a SimpleFeatureSource)?

2)如何找到距最近的多边形边缘的距离?

2) How do I find the distance to the edge of the polygon that is closest?

任何帮助将不胜感激！尤其是代码示例-我对数学和几何学有些生疏.

Any help would be highly appreciated! Especially code examples - I'm kind of rusty on math and geometry.

谢谢.

推荐答案

最简单的答案是使用SpatialIndexFeatureCollection为您完成繁重的工作，它将找到最近的多边形，然后可以检查您是否在内部或在外面.

The easiest answer is to use a SpatialIndexFeatureCollection to do the heavy lifting for you, it will find the nearest polygon, then you can check if you are inside or outside.

像这样的简单类:

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;
  }
}

可以使用一些代码来调用，例如:

Can be called using some code like:

  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);
        }

      }
    }
  }

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