I have the outline of a tubular structure. I would like to create 2 effects:
1. Make it look tubular, I'd guess with differential shading, so that it looks like the tube has been cut longitudinally and you are looking at the inside of a tube.

2. 3D: The tube is sometimes nearer or further away. I realise a 3D effect might be attainable by looking at the structure from an angle. a) How would you tilt it to get this effect, but b) Can a 3D effect be attained looking directly at it; again, I assume this would rely on shading.

Thanks,
Stephen

If you are after a perspective view, then you would need somekind of a conical gradient, which is not part of the svg specification.
To mimmick that, you may try a development build of inkscape with gradient meshes.
http://www.inkscapeforum.com/viewtopic.php?f=22&t=16091&start=25#p59697

Is there a special reason, why you want to change a 3D view angle in a 2D program?
It is so much easier to do in blender.
Inkscape cannot offer a good solution for what I could understand of your needs.