说明：  类似于VRML的控制方式 ↑前进 ↓后退 →右转 ←左转 Ctrl + →右平移 Ctrl + ←左平移 按住鼠标左键，可以通过鼠标上下左右转动视角
(Control similar to the VRML forward ↑ ↓ ← → turn right back left Ctrl+ → Ctrl+ ← left and right translation translation hold the left mouse button, the mouse up and down through the rotation angle)