Greetings, I think most of us do distributed computation, but what about distributed visualization?
In particular, here's what I have in mind. I'm running some PETSc timestepping simulations on a small beowulf, which will soon move to a large beowulf. I'd like to be able to do real-time timestep viewing of a distributed 3-D dataset. So I coded up a link between PETSc and geomview, in which each processor generates the triangulation of an isoquant contour in its local dataset of a PETSc distributed array object (DA), plus one shadow node in each direction so there are no gaps. (This next part is unimplemented, but) it then sends that triangulation to node 0. (This part is implemented) node 0 then sends the triangle data to geomview in a separate process which was forked from the PETSc program earlier (only on node 0). Output at http://lyre.mit.edu/~powell/petscgeom.html is real pretty, but hardly new, lots of people do contour surfaces. As you can see, it exposes a bug in geomview's transparency rendering, geomview needs a depth sorter to do that right, but it looks beautiful as long as you look in the right direction- or turn off transparency. :-) What I think _is_ new is the ability to generate these triangulations in real time in a distributed fashion, after every timestep or Newton iteration, in the same app that's generating the data. Does anyone know of other packages which do this, free or non-? I'm going to package the petscgeom library that does this real soon, just looking for ideas for now. In the meantime, I'm attaching the library's TODO list, as food for thought. Moving beyond this: my current library only does triangulated contour surfaces, there are also luminance/opacity-based visualization concepts, and all kinds of flow visualization schemes, all of which would be fun to do in parallel. Also, the PETSc DA is a structured grid, my library currently further requires a cartesian grid with uniform spacing (though x, y and z spacings can be different). Unstructured grids would require a new PETSc distributed object which doesn't yet exist... Zeen, -Adam P. GPG fingerprint: D54D 1AEE B11C CE9B A02B C5DD 526F 01E8 564E E4B6 Welcome to the best software in the world today cafe!
Stuff to do for PETSc-Geomview: - Get the triangles into some kind of distributed object, like a vector, but of flexible size. Then provide a mechanism for gathering them all to node zero for display in Geomview. - Use Geomview's binary format to significantly compress the data stream in the pipe and improve resolution over the ASCII transfer. - Merge the corner points so instead of three unique points for each triangle, we share corner points with adjacent triangles, cutting back enormously on the internal storage/communication requirements as well as the amount of data which must be piped to Geomview. Hopefully do this as-we-go to avoid multiple passes through the data -- want to do everything in cache if possible. - Manipulate triangles to reduce the number of triangles being sent to Geomview (and accelerate rotation there too!). Maybe do this with Evolver-style routines e.g. equiangulate, eliminate small edges, eliminate edges with low curvature at both endpoints, though we don't want to alter the triangulation too much. - Provide for animation by repeated generation and display of triangulations at various stored timesteps with a controlled framerate. Automate the production of mpeg movies of such animations. - Implement local disc storage of vectors, in order to store timesteps locally at each node for rapid production of such movies from a data set too large to fit into (distributed) memory. Yeah, baby!
