LANG: VRML and meshes

Scott Nelson (
Thu, 1 Dec 1994 12:37:42 -0800

We would appreciate feedback on the following info. We are
attempting to merge the new VRML spec into our existing
PACT data system which is used for scientific data and
3D computational meshes (finite element, finite difference
sorts of meshes).

One thing that PACT lacks is the ability to describe solids.
This is where VRML comes in to play. As an example, we
constructed a VRML (actually an OpenInventor) file consisting
of 120,000 mesh elements to get an idea of how quickly something
like ivview could deal with it. Needless to say, it was VERY
slow. This is why we would like to put VRML into PACT since
PACT handles large meshes, vector fields, surfaces, etc. very
well and there are numerous cross platform viewers available
for the existing standard.

The advantage that mesh viewers typically have is that they know
that they are looking at a mesh. Thus, instead of displaying
all 125,000 elements, they only worry about the small number of
visible surfaces (meshes typically don't have things like transparency
although we would like it).

PACT (actually the PDB data subset) is freely available from the
Lawrence Livermore National Laboratory at:

and is used in many projects, including the National Grid Project.
The point that is missing is the ability to display the pre-
meshed objects with the mesh (to see how well the mesher actually
did). PACT also supports large quantities of data efficiently, for

using ivview and a VRML file (actually OpenInventor) took about
3 minutes to display the 50x50x50 data set. Typical mesh tools
do the same in seconds because they know more about the data.

Thus although VRML is great for small virtual reality scenes, to display
scientific 3D data sets along with data is cumbersum. What we would
need to add to VRML is time sequencing (animation) so that the
scene changes (based on the position of some slider which maps to
a linear indexer). Perhaps this is what CVML promises??? Remember,
out solids and meshs have to 'move' at the same rate (weather simulations,
DYNA3D simulations of cars crashing into telephone poles, etc).

Our final motivation is cross platform usability (UNIX, PC, MAC) in that
everyone should be able to see basically the same scene but the
UNIX versions would be shaded, the PC and MAC versions would be wire
grids, etc. This is another 'benifit' of PACT, you can cheeply lump all
of the descriptors into the file and let the user determine what level
of detail to show. The alternative is to let the viewer extract a simplier
level of detail from the data, which might be OK on a speedy system.

Does anyone have an feedback on the above. We are hoping that someone
more familiar with large solids data sets is already looking into this.
Our main experience is in meshes (regular and non-regular), vector fields,
molecular data, etc. Otherwise, we'll task ourselves to do it...

Any info is greatly appreciated.

Scott Nelson


+---------------------------------------------------------+ |Scott D. Nelson B131 Rm2074 | |Lawrence Livermore National Laboratory | |7000 East Ave., L-153 | |Livermore CA 94550 | +---------------------------------------------------------+