[Rtk-users] rtkForwardProjections Segmentation fault...

[Steven Pollmann]

Hello RTK Users,

We have noticed some problems with RTK's forward projection software (rtkForwardProjections) using CUDA.  Originally, using a build we have been using from July 2013 (v1,0 rc3, commit ID 2dabe6a04cf33c0da45907efdf03d427b4473adc dated July 03, 2013), GPU Forward Projection would complete, but would leave some sort of aliasing artifacts in the projections that were not present when rtkForwardProjections was run using only the CPU methods (Joseph method, or RayCastInterpolator, changing --method commandline option, at the time).  

The next time we tried using a newer build of openRTK to perform some forward projections using the GPU/CUDA was later in the year.  However, I believe some CUDA memory management changes were made, and a forward projection could no longer be attempted due to running out of memory (and rtkForwardProjections being unable to chunk. or split up the volume to forward project).  (Our GPU at the time was an Nvidia GTX 770 with 4GB vram).

More recently, we acquired an Nvidia GTX Titan Black with 6GB vram, running driver version 337.25 on Xubuntu 14.04, and I attempted a forward projection using the latest OPENRTK (v1.0.0, July 10, 2014 commit 8646fbdc3b01b439ae37c1d7084e2e68d155c3a5).  We no longer get the "out of memory" errors (this build still causes the GTX770 to complain of memory), but rather a Segmentation Fault when trying to do the forward projection.  The Segmentation Fault occurs after it has read in the 3D Volume, when it is "Projection Volume...".  The failure is immediate.  Again, if using just the CPU to do the forward projections, everything seems to work fine.

Anyhow, I was wondering if anyone had any insight into this issue?

Our scanners produce fairly large volumes (1024x1024x680) that we are interested in performing some iterative reconstructions on.

I've uploaded a sample dataset (a Rubiks Cube volume) onto Google drive at the following link.  Due to the rtkForwardProjections program being unable to "chunk", or "divide" the dataset, I think you would need a substantial amount of video memory (6GB or more) to test this dataset, and experience the Segmentation Fault. 

https://drive.google.com/folderview?id=0B2rwn1Vax7UydVhudHlSZGlXVDQ&usp=sharing

There, you should be able to download the Rubiks MHD and Raw Volume file, the Geometry File, and a script file containing the forward projection commands we are using.

Let me know if any other information would be useful.

Thanks!

Steve