[vtkusers] different behavior between ascii and binary ensight gold reader

[Robert Maynard]

Hi Georg,

You are correct that a more efficient solution is possible. After reading
the Ensight Gold binary format (
http://www-vis.lbl.gov/NERSC/Software/ensight/doc/OnlineHelp/UM-C11.pdf ) I
have discovered how you can do this more efficiently.

If you are start at 11-37 you will see that they state:

"Note 3: Efficient reading of each file (especially binary) is facilitated
by
appending each file with a file index. A file index contains appropriate
information to access the file byte positions of each time step in the
file. (EnSight
automatically appends a file index to each file when exporting in transient
single
file format.) If used, the file index must follow the last END TIME STEP
wrapper in each file."

File Index Usage:
ASCII, Binary, Item, Description
“%20d\n”, sizeof(int), n, Total number of data time steps in the file.
“%20d\n”, sizeof(long), fb1, File byte loc for contents of 1st time step*
“%20d\n”, sizeof(long), fb2, File byte loc for contents of 2nd time step*
. . .,  . . .,  . . .,  . . .
“%20d\n”, sizeof(long), fbn, File byte loc for contents of nth time step*
“%20d\n”, sizeof(int), flag, Miscellaneous flag (= 0 for now)
“%20d\n”, sizeof(long), fb, of item n File byte loc for Item n above
“%s\n”, sizeof(char)*80, “FILE_INDEX”, File index keyword
* Each file byte location is the first byte that follows the BEGIN TIME
STEP record


To me the best way is to read the file in reverse looking for FILE_INDEX as
the last 80 characters. From that you parse the previous long as
the new seek position which jumps you to the start of the file index
records. After reading the file index records you have a lookup table for
all seek positions of the time steps in that ensight file.


On Wed, Mar 6, 2013 at 4:23 AM, Georg Hammerl <hammerl at lnm.mw.tum.de> wrote:

> Hello,
>
> I have already posted this issue on the paraview mailing list, but then I
> realized that it is more of a VTK problem.
> I can load the first time step of my results but when I switch to the next
> step (in which 4 points are added), paraview freezes and htop shows 100%
> load for this process. Surprisingly, this only happens when I use binary
> ensight gold format. The same results written in ascii ensight gold format
> work. The ens_checker tells me for both cases that I have valid output
> files.
>
> Meanwhile I had a look into the source code and discovered the issue.
> Whenever the variable-files are read for a time steps greater than 1,
> Paraview has to jump in the binary file to the desired timestep. This is
> done by partially parsing and skipping blocks until the correct "BEGIN TIME
> STEP" is found. In order to skip the correct block length, Paraview uses
> the number of points (numPts) from the current geometry step. This breaks
> with a varying number of points per timestep.
> As an example my first step contains 2 points and the second step 6
> points, therefore when Paraview skips the first time step, it skips a block
> length equivalent to 6 points. The correct number would be 2 points. It
> therefore skips past the next "BEGIN TIME STEP".
>
> In order to verify my theory I have implemented a little hack which looks
> for the next "BEGIN TIME STEP" by brute force. In case someone wants to try
> this I have attached a patch which can be used in conjunction with the
> attached examples.
>
> A clean solution would be to skip the correct number of points for every
> given timestep. Unfortunately I do not have enough insight into the VTK
> ensight reader to implement this and would appreciate any help in finding a
> clean solution to this.
>
> Cheers,
>
> Georg
>
> --
> Dipl.-Ing. Georg Hammerl
> Lehrstuhl für Numerische Mechanik
> Technische Universität München
> Boltzmannstrasse 15, D-85747 Garching b. München
> phone +49 89 289 15237
> fax +49 89 289 15301
> hammerl at lnm.mw.tum.de
> http://www.lnm.mw.tum.de
>
>
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-- 
Robert Maynard
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