[vtkusers] Weird problems with my volume reader...

[Charles Boivin]

Hello,

I am currently in the process of writing a volume reader for my own
type of data. The data is on a structured cartesian grid, and is all
stored in one file. I decided to base my reader on the vtkVolume16Reader
so I, too, derived a class from vtkVolumeReader.

Now, this is my first try with 3D structured data, so I am still not
too familiar with the process. I have previously written readers for
vtkPolyData data structures, and things went well there. First thing I
noticed is that, for my previous reader, most of the work was done in
the Execute() member function. For the volume reader, there seems to be
both a ExecuteInformation() and a ExecuteData() functions. I read the
description of my file and data is ExecuteInformation() and read the
actual data from disk in ExecuteData(). Is this what should be done?

I believe the data gets read properly because I am somehow able to
display some of it, and it looks alright. However, there is some strange
behavior that I am not quite sure how to fix. First of all, the data
seems to be read *several* times before it is displayed. ExecuteData()
is called about 2-3 times before the first display, and then, if I
change the array I want displayed, the data is read once more. Should I
be setting some flag saying that the data has been read? That seemed to
be taken care of automatically in the vtkPolyData reader I wrote before
(I derived that one from vtkPolyDataSource).. is this a case where the
volume reader behave differently?

There is also one last strange behavior: I load 7 different scalars in
my data, and stored them the same way I would store point data in the
vtkPolyData reader. The *order* of the scalars seems to change once I
pass the output to my filters, however. The last array now seems to be
the first one, with all other arrays being shifted on spot. As anyone
seen such a behavior before, and if so, could they provide some hints as
to where things might be going wrong? I can provide some sample code if
necessary, but I figured this email was already long enough as it is...
I am trying to see if some of you have experienced these problems before
and if so, what you did to fix them.

Many thanks in advance,

Charles Boivin