AVS 5's tube module is a very useful module. It converts lines in a geometry into eight-sided cylinders of a given radius, and is thus excellent for ``thickening'' lines to be more clearly visible.
However, it has a major drawback. When it is inserted into a network between a hedgehog or streamlines module and the geometry viewer module, it breaks the normally invisible, automatic upstream_transform link between these modules. This link is used to tell the hedgehog or streamlines module that its sample points have changed, and the hedgehogs or streamlines must be recalculated.
Worst, though, is that reconnecting the upstream_transform link does not restore things to a sane condition as it should. To work properly, the output of the hedgehog or streamlines module must be directly connected to the geometry viewer, and the geometry viewer's upstream_transform output must be directly connected to the hedgehog or streamlines module. If this is not the case, it is impossible to change the hedgehog or streamlines module's set of sample points from their default, which is a plane in the middle of the dataset. For most of the visualisations in this project, the hedgehogs or streamlines were desired at other planes, such as ground level.
Unfortunately, this is a hard limitation of AVS 5, and there is no real solution other than to live with the limitation. The best solution, however, would be to modify the tube module (in source code) to allow it to properly propagate the upstream_transform module upwards in the network.
The particle advector module also suffers from similar problems, but is more well behaved when the upstream_transform links are reconnected.