Line width (tube diameter) is not controllable with OSPRay

[bastian]

I am visualizing lines loaded from vtu files as tubes and I don’t succeed at controlling their diameters.

The diameter somehow varies from file to file even though the display settings are the same.

This is super weird and annoying.

I tested Paraview 5.7.0, 5.8.0 and 5.8.1.
The issue is observed with OSPRay raycaster and OSPRay pathtracer; when disabling Ray Tracing all lines have the same width.

Am I missing a setting?
Is it a known bug?
Is there a workaround?

Here are the sample files and a state file (Paraview 5.8.0) illustrating the issue:
collision_dry_distances_000012.vtu (844 Bytes)
collision_dry_distances_000013.vtu (844 Bytes)
state.pvsm (246.6 KB)

I am pretty sure now that the diameter scales with the total length of all line segments. This can easily be demonstrated by applying a transform filter:

So … where can I assign the absolute, exact tube diameter?

[bastian]

Similarly, the diameter of arrow glyphs depends on their length.

Not being able to specify the actual diameter of these tubes makes it impossible to render network-like structures, … think of a spider web.

[Dave_DeMarle (Dave DeMarle (Intel))]

This is a known bug. As you have surmised, the point=>sphere and line=>cylinder radius for the ray tracers is, by default, set via a function of the object’s bounding box and the vtkProperty.pointsize/linewidth control. A workaround for you might be to use the “Scale Array” control, which lets you choose a point aligned array to set the radius at each point, but the weird way that goes through a lookup table, may be problematic.

I’ve started on a fix here.

[Dave_DeMarle (Dave DeMarle (Intel))]

@bastian - as described over on this post the merge request is now going through review. I expect it to appear in 5.9.rc1 in a week or two.

[bastian]

@Dave_DeMarle Awesome! I will wait for it to be released then and mark this thread as solved once that is the case.
Thanks a bunch for your work.

[bastian]

It looks like this feature has not made it into ParaView yet ,
https://gitlab.kitware.com/paraview/paraview/-/merge_requests/4335
yet it would be such an improvement!

To underline why it would be really helpful to be able to precisely assign line/tube diameters consider a viualization of wireframes. Let me give you an example:

So I set up a state for the visualization of 8 falling rings:

Looks good to me. However, using the exact same state for 24 falling rings of which each is identical to the eight above is less pleasing to my eyes:

But even the line widths of the eight rings look thicker later in time and I have no clue why:

For the visualization of e.g. arrows it’s a good thing to have the tubes scale with length, but in case of wireframes I don’t think it is.

[bastian]

Ahh never mind I must have been blind! There is “Each Exact” now. Will check it out!

[bastian]

@Dave_DeMarle - “Each exact” does not seem to work for wireframes. It has my CPU go crazy until I eventually shut down the non-responding ParaView instance.

Here is a video demonstrating the issue:
peek_scaling_each_exact_simpleexample.mp4