Update( )在VTK中的作用是什么？

#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>
#include <vtkPolyDataMapper.h>
#include <vtkActor.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>

int main(int, char *[])
{
    // 创建一个球体数据源
    vtkSmartPointer<vtkSphereSource> sphereSource = 
        vtkSmartPointer<vtkSphereSource>::New();
    sphereSource->SetRadius(5.0);
    sphereSource->Update(); // 更新数据源

    // 创建一个映射器
    vtkSmartPointer<vtkPolyDataMapper> mapper = 
        vtkSmartPointer<vtkPolyDataMapper>::New();
    mapper->SetInputConnection(sphereSource->GetOutputPort());

    // 创建一个演员并设置其映射器
    vtkSmartPointer<vtkActor> actor = 
        vtkSmartPointer<vtkActor>::New();
    actor->SetMapper(mapper);

    // 创建一个渲染器和渲染窗口
    vtkSmartPointer<vtkRenderer> renderer = 
        vtkSmartPointer<vtkRenderer>::New();
    vtkSmartPointer<vtkRenderWindow> renderWindow = 
        vtkSmartPointer<vtkRenderWindow>::New();
    renderWindow->AddRenderer(renderer);

    // 创建一个交互器并设置其渲染窗口
    vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = 
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
    renderWindowInteractor->SetRenderWindow(renderWindow);

    // 添加演员到渲染器
    renderer->AddActor(actor);

    // 开始渲染循环
    renderWindow->Render();
    renderWindowInteractor->Start();

    return EXIT_SUCCESS;
}