[vtkusers] Volume rendering problem

[Elvis Stansvik]

2016-08-11 11:37 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:

> 2016-08-11 11:18 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>
>> 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!
>>
>
> Sorry, shortly after sending this I think I got one step closer to an
> explanation. The file from which I load this second, larger, volume is
> actually a concatenation of several files, and I just tried loading one of
> the files separately and it worked fine (the rendering looks as expected).
> So something is probably wrong in the script I use for concatenating HDF5
> files. I'll do some digging there.
>

There seems to be nothing wrong with the concatenation script I'm using.
I've now tried creating smaller volumes by not concatenating the full set
of files, and up until a resulting volume of around ~2500x300x300 it works
okay, but if I extend the volume more than that, the rendering fails like
described previously. It's quite strange :/ And I don't think I'm hitting
some out-of-memory condition inside VTK, since it normally prints nice
errors and crashes if that happens.

Elvis


> Elvis
>
>
>>
>> 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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