Hibernate Spatial - Query within an X kilometer ra

问题:

I am new to Hibernate Spatial, and am trying to perform a simple query of objects within a given radius. I've created a number of entries in my database with properties corresponding to a latitude and longitude, using data from Google Maps and other sources. This property is defined like this in my Entity class:

@Column
@Type(type = "org.hibernate.spatial.GeometryType")
private Point coordinates = null;

I'm now trying to figure out how to do a search of all entity objects that have coordinates that fall within a radius of x kilometers from a given point. For example, I'd like to find objects that fall within a 50 kilometer radius of the point (12.34567, -76.54321). However, I can't find any examples or tutorials that would explain how to do this in Hibernate Spatial.

Can anyone give me any information on how a query like this can be constructed?

回答1:

See this resource for a tutorial with "Spatial Queries", which a special dialect and the JTS library (Open Source).

Basically you do the following (copy/paste from the referenced page):

import com.vividsolutions.jts.geom.Geometry;
import com.vividsolutions.jts.geom.Point;
import com.vividsolutions.jts.io.ParseException;
import com.vividsolutions.jts.io.WKTReader;
import util.JPAUtil;

import javax.persistence.EntityManager;
import javax.persistence.Query;
import java.util.Date;
import java.util.List;

.......

private List find(String wktFilter) {
    Geometry filter = wktToGeometry(wktFilter);
    EntityManager em = JPAUtil.createEntityManager();
    em.getTransaction().begin();
    Query query = em.createQuery("select e from Event e where within(e.location, :filter) = true", Event.class);
    query.setParameter("filter", filter);
    return query.getResultList();
}

private Geometry wktToGeometry(String wktPoint) {
    WKTReader fromText = new WKTReader();
    Geometry geom = null;
    try {
        geom = fromText.read(wktPoint);
    } catch (ParseException e) {
        throw new RuntimeException("Not a WKT string:" + wktPoint);
    }
    return geom;
}

For generating a circle, see this resource (search for "Arcs, Circles and Curves"). Again a copy/paste from there:

//this method replaces the above wktToGeometry() method
private static Geometry createCircle(double x, double y, final double RADIUS) {
  GeometricShapeFactory shapeFactory = new GeometricShapeFactory();
  shapeFactory.setNumPoints(32);
  shapeFactory.setCentre(new Coordinate(x, y));//there are your coordinates
  shapeFactory.setSize(RADIUS * 2);//this is how you set the radius
  return shapeFactory.createCircle();
}

Besides you always have the workaround, in which to add some additional fields ( mapped withinsertable=false, updatable=false) to map to the same columns used by the org.hibernate.spatial.GeometryType and then use them in your query. For computing the distance, check the euclidian distance formula.