[visit-users] Using subset to plot a 3D surface with nice lighting - problem with large data set?

Hank Childs hankchilds at gmail.com
Tue Mar 23 23:54:39 EDT 2010


Hi Nick,

I think this is best described as a bug, but I also understand why
VisIt is doing what it is doing.

When VisIt tries to decide what kind of file it is looking at, it uses
the first file in your .visit file to make that decision.  Since that
file has no geometry, VisIt doesn't know what to make of it ... it
arbitrarily decides it is a point mesh.  (I personally think a 3D
volume would be a safer assumption ... but the point is: it doesn't
think you have a surface mesh.)

So it then executes, operating under the assumption that it has a
point mesh.  Of course, when it finally goes to read all of the data,
it could check the assumption it is making ... but it doesn't.

You've hit quite a corner case here ... the common multi-block use
case involves a file format that can describe what type of data is in
the file, even in the case of an empty domain.  But since you are
using .visit files in conjunction with VTK, that didn't happen.

Worse, fixing this problem would require VisIt to change its logic for
evaluating what kind of data it is processing.  This is clearly a
noble goal, but also a time consuming one.  And, although it would
help your corner case, it wouldn't help much else.

So how about this?: can you change your .visit file to only reference
domains that actually have data?  Note: because VisIt tries to save
time by assuming the number of domains is fixed, you will need to
enable "Treat all databases as time-varying" under
Options->Preferences if you want to take this path.

Best regards,
Hank

On Tue, Mar 23, 2010 at 9:57 AM, Nick Hawker
<nickhawker49 at googlemail.com> wrote:
> Dear all,
>
> I have been using the subset plot to render a surface mesh. Using subset
> allows you to get nice lighting on the surface. When the total underlying
> domain (the surface mesh sits inside this domain and is made of triangles of
> dimensions comparable to the underlying grid size) is 200x200x200, it works
> great. However, when I try to plot a 400x400x400 result the nice lighting
> effects disappear. I can still see the surface fine and can see the
> different domains with the subset plot, if I give them different colours. I
> can also step through fine and the plot shows the surface correctly but
> still without the lighting effects. So basically, it looks like a flat disc
> rather than a sphere (for example). Using a mesh plot I can see all the
> triangles properly and so on, hence I don't think there is a problem with my
> data.
>
> The domain is split into 64 parts and each part has a separate vtk file. I
> use a .visit file to tell it where all the parts are. When opening the
> .visit file, I have the problem described above. However, when opening just
> a single vtk file and doing a subset plot, everything works fine. That is to
> say, it is appropriately lit. This doesn't work in 1.11.1 since the subset
> option is not available for data with just one domain. It works in 1.12.2
> though.
>
> Could this be a bug in VisIt? I was initially using 1.11.1 but have the same
> problem with 1.12.2. Anyone have any ideas what is going on here?
>
> Many thanks,
>
> Nick
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