[vtkusers] Volume rendering problem

[Elvis Stansvik]

Hi all,

I'm wrestling with a volume rendering problem.

I've set up a very basic pipeline that just renders a volume.

As source it uses a custom reader I wrote that loads a volume from a HDF5
dataset (float).

It seemed to be working fine with the volume I had been testing with (see
attached works_fine.png), which was a 120x120x2000. In addition to the the
rendering itself, the screenshot shows a histogram plot I was using for
debugging, as well as some editor controls I use to modify the
color/opacity transfer function.

I then tested with another volume which is larger (300x300x5000), but apart
from that has pretty much the same characteristic for its scalar values as
the first one, and all of a sudden I don't see anything. See the attached
not_working.png, which shows the setup using the problematic volume.

As you can in the histogram, there's a lot of voxel values roughly around
1, much like in the first volume, so I would expect that with the same
transfer functions (black color, and an opacity ramp from 0.0,0.0 up to
5.0,1.0), I should see _something_.

I'm pretty sure I'm missing something basic here, but does anyone have an
idea why I get the expected rendering with my smaller volume, but not with
the bigger one?

Thanks a lot for any advice!

Elvis

PS. If you're confused by the range of the vtkAxisActor that you see in the
screenshots, when comparing to the the volume sizes I stated above, it's
because my custom render currently hardcodes the spacing to 0.2. DS.
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