How to pick a cell from vtkPolyData by coordinate

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3 
vtkDataSetMapper* mapper = dynamic_cast<vtkDataSetMapper*>(actor->GetMapper());
vtkDataSet* data = mapper->GetInput();

vtkNew<vtkExtractEdges> edges;
edges->SetInputData(data);
edges->Update();
vtkPolyData *poly = edges->GetOutput();

int* clickpos = this->GetInteractor()->GetEventPosition();
vtkNew<vtkPropPicker>  picker;
picker->Pick(clickpos[0], clickpos[1], 0, GetRenderer());
double *clickedcoord = picker->GetPickPosition();

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//Then, I want to selectithe line from "poly" which near the "clickedcoord".