BOV reader semi-support time steps

[shaomeng]

To reproduce:

1. Open VAPOR, import BOV file: /glade/p/cisl/vast/vapor/Bugs/BOV_Bugs/bug3.bov
2. Create and enable a volume renderer.
3. Advance time step by 1. Notice that the rendering remains the same, though the 2 time steps clearly point to different data files.

[sgpearse]

Visit's BOV specification doesn't mention specifying multiple time steps like this. IMO, this is an enhancement.

BOV Specification: section 3, page 9
https://wci.llnl.gov/sites/wci/files/2020-08/GettingDataIntoVisIt2.0.0.pdf

[clyne]

@shaomeng are you sure the file you created (bug3.bov) is how time-varying data sets are supported? My interpretation of VisIt's documentation is that you can only have one set of keyword-value pairs per file. I.e. You need a single file per time step or per variable. I could be wrong, however.

[shaomeng]

@clyne VAPOR shows 2 time steps available with the bov file in question, and a user is able to switch between these 2 time steps. It's OK to not show 2 time steps if you don't support 2 time steps.

Re VisIt comparison: I feel we're in a state where when VAPOR behaves differently from VisIt and its documentation, it's considered a VAPOR uniqueness. When VAPOR exhibits a bug (or bad behavior in general) and VisIt behaves the same, it's considered "see, VisIt does the same." This isn't a good situation to be in.

[clyne]

Agreed that it should not show two time steps. I think a reasonable behavior for repeating the same keyword multiple times is to simply accept the last value found.

[sgpearse]

@shaomeng, you are observing #2812 here, which is not BOV related. If you import one timestep of a wrf file, you can advance the timesteps as well.