geotools：how to find distance from a point to closest polygon in shapefile

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).

我有一个shp文件，里面存有一些多边形。在本例中，多边形代表内陆水体（像湖和类似的东西）。

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.

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，无论是在水里还是水外）。我将每隔一段时间从对象中提取一个采样点并对其进行测试。

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.

这个系统是用Java写的，我已经导入了Geotools-snapshot-17。但是如果有更易用的，就没必要用这个。

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

要测试该点是否在水里（也就是，在多边形内部），方法是这样的：

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，问题是：

1) If the point is NOT in a polygon, how do I find the nearest polygon in the source (being a SimpleFeatureSource)?如果该点不在任何多边形内，如果找到理它最近的多边形呢？

2) How do I find the distance to the edge of the polygon that is closest?如果查找离最近的多边形的距离？

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

Thank you.

https://stackoverflow.com/questions/44045598/java-geotools-how-to-find-distance-from-a-point-to-closest-polygon-in-shape-fil?r=SearchResults

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.

最简单的方法是使用SpatialIndexFeatureCollection来帮你做这份沉重的活，它会查找到最近的多边形，然后你可以检查是否在内部还是外部。

So a simple class like：

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;
  }
}

>>GeoTools入门（六）-- 查询那点事：https://blog.csdn.net/oYinHeZhiGuang/article/details/118316074