点查询点的实现

图形查询利用的是查询图形与被查询图形的拓扑关系，因而点查询点的方式是利用点与点之间的拓扑关系的，而点与点之间的只有重合（点的坐标完全一致）、相离两种，当我点击地图上某点时坐标不可能与要查询的点要素完全一致，因此重合的方式是不可取的，再看ArcGIS api for Silverlight中提供的查询拓扑关系如下：

SpatialRelationship.esriSpatialRelContains：Part or all of a feature from feature class 1 is contained within a feature from feature class 2，要素一局部或全部包含在要素二中（包含、局部包含）；

esriSpatialRelEnvelopeIntersects：The feature from feature class 1 crosses a feature from feature class 2，要素一穿过要素二（线线、线面、面面相交）；

esriSpatialRelEnvelopeIntersects：The envelope of feature class 1 intersects with the envelope of feature class 2，要素一的外接矩形与要素二的外接矩形相交；

esriSpatialRelIndexIntersects：The envelope of the query feature class intersects the index entry for the target feature class，查询图形的外接矩形与目标要素相交；

esriSpatialRelIntersects：Part of a feature from feature class 1 is contained in a feature from feature class 2，要素一的一部分包含在要素二中（包含、相交）；

esriSpatialRelOverlaps：Features from feature class 1 overlap features in feature class 2，要素一与要素二重叠（重叠关系）；

esriSpatialRelRelation：Indicates that a spatial relationship function will be used，用于特殊的空间关系，即可用于自定义上述几种空间关系的组合；

esriSpatialRelTouches：The feature from feature class 1 touches the border of a feature from feature class 2，要素一与要素二的边缘相接（相邻）；

esriSpatialRelWithin：The feature from feature class 1 is completely enclosed by the feature from feature class 2，要素一完全在要素二内（包含）

由上可得，Api提供的空间关系不适用于点查询点，那么可以通过其他方式实现，比如说，将查询点扩散成面，这样即成为查询点周围一定区域内的要素了，点化面代码如下：

        /// <summary>
        /// 以当前点作为中心点获取一定方框范围
        /// </summary>
        /// <param name="mapExtent"></param>当前地图范围
        /// <param name="point"></param>地图中心点
        /// <param name="pct"></param>获取方框范围的比例系数
        /// <returns></returns>
        private Envelope Expand(Envelope mapExtent, MapPoint point, double pct)
        {
            return new Envelope(
                    point.X - mapExtent.Width * (pct / 2), point.Y - mapExtent.Height * (pct / 2),
                    point.X + mapExtent.Width * (pct / 2), point.Y + mapExtent.Height * (pct / 2))
            {
                SpatialReference = mapExtent.SpatialReference
            };
        }

查询的完整代码如下

 private QueryTask task;
 private Query query;
private void Window_Loaded(object sender, RoutedEventArgs e)
        {
           
            task = new QueryTask();
            task.ExecuteCompleted += new EventHandler<QueryEventArgs>(task_ExecuteCompleted);
            task.Failed += new EventHandler<TaskFailedEventArgs>(task_Failed);
            task.Url =“http://***/arcgis/rest/services/***/FeatureServer/0”;
            query = new Query();
            query.SpatialRelationship = SpatialRelationship.esriSpatialRelIntersects;
            query.ReturnGeometry = true;
            query.OutFields.Add("*");//默认输出字段为全部
            query.OutSpatialReference = map1.SpatialReference;
        }
         void task_Failed(object sender, TaskFailedEventArgs e)
        {
            MessageBox.Show("查询失败");
            map1.Cursor = System.Windows.Input.Cursors.Help;
        }

        void task_ExecuteCompleted(object sender, QueryEventArgs e)
        {
            
            String content = "";
            if (e.IdentifyResults==null ||e.IdentifyResults.Count<=0)
            {
               map1.Cursor = System.Windows.Input.Cursors.Help;
                return;
            }
            Graphic g = e.IdentifyResults[0].Feature;
           
                foreach (var item in g.Attributes)
                {
                    content += item.Key + ":";
                    content += item.Value+"\n";
                }
                infoWindow1.IsOpen = false;
                if (e.IdentifyResults != null && e.IdentifyResults .Count > 0)
                {
                    lblContent.Content = content;//显示内容
                    //  infoWindow1.Anchor = set.Features[0].Geometry.Extent.GetCenter();
                    infoWindow1.Anchor = selPoint;//显示位置
                    infoWindow1.IsOpen = true;
                }
               map1.Cursor = System.Windows.Input.Cursors.Help;
        }

 private void map1_MouseClick(object sender, Map.MouseEventArgs e)
        {
                   query.MaxAllowableOffset = 5;
                  
                    
                    query.Geometry = this.Expand(map1.Extent,e. MapPoint,0.03);
                   // query.Geometry = e.Geometry;
                    task.ExecuteAsync(query);
                    map1.Cursor = System.Windows.Input.Cursors.Wait;
                    break;
        }

效果入下：

事实上在具体实现中，要控制查询的精度，可以根据不同的比例尺，更改点扩散为面的距离范围。