i used PolylineVolumeGeometry for drawing water pipe line，but the 3D line is not hollow！ How can i draw this geometry？
By not hollow, do you mean there are caps on the end of the line? Or do you mean you can’t go inside the volume with the camera?
The caps are not something that is currently configurable (but probably can be).
The ability to go inside the volume is determined by the Appearance. For example if you are using PerInstanceColorAppearance, you need to specify closed=false.