open software
read point cloud
black background
Hold down the left button and move the mouse to select top
Press and hold the left button and move the mouse to select Draw VerticalSection
Click the mouse to draw the area and width for the first time (left button, left button, pull the mouse, left button)
Move to the second window and click the left button
After selecting move, left-click to move up the area width, right-click to move down the area width
Zoom out, zoom in, view the modification in the second window