Identify点选优化

问题描述:
    在arcgis server 中直接以鼠标按下的点进行点选时,如果地图的比例尺较小(如全图状态),点选会非常困难,必须'恰好'点在特征上才能查询到信息;如果放大地图,使地图比例尺变大,虽然点选非常容易,但在没有点到特征上时,也能选中特征,给人以错误的视觉感受.
问题产生原因:
    直接以鼠标按下的点作为查询Geometry,没有考虑到当前地图窗口的范围.
解决办法(考虑当前地图窗口的范围):
    1.获得鼠标按下的点
        ESRI.ArcGIS.ADF.Web.UI.WebControls.PointEventArgs ctrlPointEventArgs = (ESRI.ArcGIS.ADF.Web.UI.WebControls.PointEventArgs)args;
        System.Drawing.Point screenPoint = ctrlPointEventArgs.ScreenPoint;
        ESRI.ArcGIS.ADF.Web.Geometry.Point point = ESRI.ArcGIS.ADF.Web.Geometry.Point.ToMapPoint(screenPoint, map.GetTransformationParams(ESRI.ArcGIS.ADF.Web.Geometry.TransformationDirection.ToMap));
    2.根据当前的地图范围,扩展鼠标点,形成一个信封
        ESRI.ArcGIS.ADF.Web.Geometry.Envelope adfEnvelopeCurrentExtent = point.Expand(1, map.Extent);
    3.使用信封作为查询的Geometry,形成空间查询过滤器
        ESRI.ArcGIS.ADF.Web.SpatialFilter adfSpatialFilter = new ESRI.ArcGIS.ADF.Web.SpatialFilter();
        adfSpatialFilter.Geometry = adfEnvelopeCurrentExtent as ESRI.ArcGIS.ADF.Web.Geometry.Geometry;
        adfSpatialFilter.MaxRecords = 1;
        adfSpatialFilter.ReturnADFGeometries = true;
    4.执行查询
        System.Data.DataTable dtResult = cmnagsQueryFunctionality.Query(cmnagsMapFunctionality.Name, lids[i], adfSpatialFilter);