void IVisitor.Visit(IAlgorithm alg)
{
//thong tin bang dau:from,by,result duoc dua vao bag truoc
//khi xet den thuat toan 2, from,result cua bag la result cua thuat toan 1
//by cua thuat toan tu cai dat san truoc khi duoc visit
ISpatialBag spBag=(ISpatialBag)this._bag;
alg.SetResultLayer(spBag.ResultFeatureLayer);
//MessageBox.Show(_index.ToString());
ISpatialAlgrorithm spAlg = (ISpatialAlgrorithm)alg;
//spAlg.SetLayers(spBag.FromFeatureLayer, spBag.ByFeatureLayer);
spAlg.FromLayer = spBag.FromFeatureLayer;
spAlg.SetResultLayer(spBag.ResultFeatureLayer);
spBag.ResultSelectionSet = spAlg.Execute();
spBag.ResultFeatureLayer = spAlg.GetResultLayer();
spBag.FromFeatureLayer = spAlg.GetResultLayer();
_index++;
}