SciVisFall2007/Assignment 3/FAQ

From VistrailsWiki
Revision as of 18:44, 21 November 2007 by Eranders (talk | contribs)
Jump to navigation Jump to search

Q: I cannot read the tokamak datasets. VisTrails crashes regardless of what I try to do!

A: The version of VisTrails distributed uses a different version of the VTK libraries than those used to generate the dataset. To fix this, we have substituted the dataset to be used for the problems relating to Iso-Surfacing. The problems and general dataset properties remain the same, but the underlying data description is a bit different.


Q: In problem 1c, what do you mean by "change from the initial conditions?"

A: The initial condition here is meant to be time-step 1, with the change being exhibited by changing the time-step being visualized.


Q: In problem 1c, what do you mean by "the two data?" Is it the two time steps?

A: In this case, visualizing the two data refers to the fact that there is a scalar field as well as a vector field in each data set. What method(s) can be used to visualize both of these types of data (vector field with a scalar field) simultaneously?


Q: I'm having problems generating contour spectra. It gives me a "Volume May Not Be Closed" error, am I doing something wrong?

A: No, you are probably not doing anything wrong. All contours that you generate for the Columbia River datasets will NOT be closed. This is something that you should expect. In the PythonSource that generates the contours, I put a check in there on purpose for exactly this sort of situation. Examine the PythonSource module generating the spectra and edit it to NOT use volume information and instead use some other metric(s). These metrics are explained in detail in the class documentation for the vtkMassProperties class Simply replace the GetVolume() call to the metric you wish to use.


Q: In problem 1, you have vertex-centered unstructured hexahedral mesh for the dataset of Colombia river. That's different with tetrahedral mesh we usually use. I looked up for the vtk function for hexahedral in vistrail to try to extract the scalar and normal vector but can not find anything relevant. Do you have any references about that?

A: VTK's classes are generally smarter to handle any type of volumetric data. In this case, we have hexahedral meshes instead of tetrahedral ones. The iso-contour filters and stream tracing filters handle all types of data. The only change you need to be aware of is if you are trying to volume render the data. Try using vtkUnstructuredGridVolumeZSweepMapper instead of the standard raycaster or other volume mapper. Beware, though, this method could be quite slow. I recommend using a DataSetMapper with a LUT or using only the iso-contouring methods.