engine的工具中实现Snapping(捕捉)

在Engine的工具(ITool)里:

OnClick事件处理函数中:

首先需要获取一个图层,作为Snapping的参照,

IFeatureLayer targetLayer

然后声明一个IMovePointFeedBack作为鼠标移动时捕捉点的显示:

IMovePointFeedback m_pMovePtFeed = new MovePointFeedback();

mFeedback = (IDisplayFeedback)m_pMovePtFeed;

ISimpleMarkerSymbol simpleMarkerSymbol = new SimpleMarkerSymbolClass();

IRgbColor pRGBColor = new RgbColorClass();

pRGBColor.Red = ;

pRGBColor.Green = ;

pRGBColor.Blue = ;

simpleMarkerSymbol.Color = pRGBColor;

simpleMarkerSymbol.Size = ;

simpleMarkerSymbol.Style = ESRI.ArcGIS.Display.esriSimpleMarkerStyle.esriSMSSquare;

ISymbol symbol = simpleMarkerSymbol as ISymbol;

symbol.ROP2 = esriRasterOpCode.esriROPNotXOrPen;

//symbol.ROP2 = esriRasterOpCode.;

m_pMovePtFeed.Symbol = (ISymbol)simpleMarkerSymbol;  

然后, 开始Feedback的显示(tmpPoint是指开始的点,其实影响不大,如果不想要源点在屏幕上的话,可以取一个在屏幕外的点):

m_pMovePtFeed.Display = mMapControl.ActiveView.ScreenDisplay;

m_pMovePtFeed.Start(tmpPoint, tmpPoint); 

在OnMouseMove事件中:

IPoint pPoint2 = null;

IPoint pPoint = pMap.ActiveView.ScreenDisplay.DisplayTransformation.ToMapPoint(x, y);

pPoint2 = Snapping(pPoint.X, pPoint.Y, targetLayer, pMap, );

if (pPoint2 == null)

pPoint2 = pPoint;

((IMovePointFeedback)mFeedback).MoveTo(pPoint2);  

其中Snapping函数即为最主要的查找函数,其功能为根据输入的点坐标在目标图层上查找最为相近的点(也即需要捕捉的点),返回该点,若没有找到则返回NULL,最后一个参数的含义是,在地图控件上,以多少个像素为单位在周边查找捕捉点.

public IPoint Snapping(double x, double y, IFeatureLayer iFeatureLyr, IMapControl3 axMapControl1,double snappingDis)

{

    IPoint iHitPoint = null;

    IMap iMap = axMapControl1.Map;

    IActiveView iView = axMapControl1.ActiveView;

    IFeatureClass iFClss = iFeatureLyr.FeatureClass;

    IPoint point = new PointClass();

    point.PutCoords(x, y);

    double length = ConvertPixelsToMapUnits(axMapControl1.ActiveView, snappingDis);

    ITopologicalOperator pTopo = point as ITopologicalOperator;

    IGeometry pGeometry = pTopo.Buffer(length).Envelope as IGeometry;

    ISpatialFilter spatialFilter = new SpatialFilterClass();

    spatialFilter.GeometryField = iFeatureLyr.FeatureClass.ShapeFieldName;

    spatialFilter.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects;

    spatialFilter.Geometry = pGeometry;

    IFeatureCursor cursor = iFClss.Search(spatialFilter, false);

    IFeature iF = cursor.NextFeature();

    if (iF == null) return null;

    IPoint iHitPt = new ESRI.ArcGIS.Geometry.Point();

    IHitTest iHitTest = iF.Shape as IHitTest;

    double hitDist = ;

    int partIndex = ;

    int vertexIndex = ;

    bool bVertexHit = false;

    // Tolerance in pixels for line hits

    double tol = ConvertPixelsToMapUnits(iView, snappingDis);

    if (iHitTest.HitTest(point, tol, esriGeometryHitPartType.esriGeometryPartBoundary,

iHitPt, ref hitDist, ref partIndex, ref vertexIndex, ref bVertexHit))

    {

iHitPoint = iHitPt;

    }

    //axMapControl1.ActiveView.Refresh();

    return iHitPoint;

}

public double ConvertPixelsToMapUnits(IActiveView pActiveView, double pixelUnits)

{

    double realWorldDisplayExtent;

    int pixelExtent;

    double sizeOfOnePixel;

    pixelExtent = pActiveView.ScreenDisplay.DisplayTransformation.get_DeviceFrame().right - pActiveView.ScreenDisplay.DisplayTransformation.get_DeviceFrame().left;

    realWorldDisplayExtent = pActiveView.ScreenDisplay.DisplayTransformation.VisibleBounds.Width;

    sizeOfOnePixel = realWorldDisplayExtent / pixelExtent;

    return pixelUnits * sizeOfOnePixel;

}

此时即可实现鼠标实时地捕捉目标图层上的对象,若需要获取当前位置的捕捉点时,则可以在相应事件(例如OnMouseDown或OnDbClick)中调用:

IPoint pPoint = ((IMovePointFeedback)mFeedback).Stop();

这时实时捕捉将会停止,若需要重新开始捕捉,则在之后调用这些语句即可:

//重新开始Snap

IPoint tmpPoint = new PointClass();

tmpPoint.PutCoords(pMap.Extent.XMin - , pMap.Extent.YMin - );

IMovePointFeedback m_pMovePtFeed = (IMovePointFeedback)mFeedback;

m_pMovePtFeed.Display = pMap.ActiveView.ScreenDisplay;

m_pMovePtFeed.Start(tmpPoint, tmpPoint);