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：

 1         /// <summary> 2         /// 以当前点作为中心点获取一定方框范围 3         /// </summary> 4         /// <param name="mapExtent"></param>当前地图范围 5         /// <param name="point"></param>地图中心点 6         /// <param name="pct"></param>获取方框范围的比例系数 7         /// <returns></returns> 8         private Envelope Expand(Envelope mapExtent, MapPoint point, double pct) 9         {10             return new Envelope(11                     point.X - mapExtent.Width * (pct / 2), point.Y - mapExtent.Height * (pct / 2),12                     point.X + mapExtent.Width * (pct / 2), point.Y + mapExtent.Height * (pct / 2))13             {14                 SpatialReference = mapExtent.SpatialReference15             };16         }

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。