[Insight-users] Problem with DRR generation

[Jian Wu]

Dear ITK users:

I'm wondering if anyone have generated correction DRRs using the example 
programs GenerateProjection.cxx or DigitallyReconstructedRadiograph1.cxx.

I ran both codes using the parameters and the image given in the README.txt 
file. But the generated DRRs appear to have a different projection and image 
center than I expected.
I also tried to simply the test data in 
DigitallyReconstructedRadiograph1.cxx. Instead of using the orignal cubic 
structure, I constructed a 61x61x61 3D image with a single point at the 
center of the image. The resulting DRR has a point centered at pixel index 
(81, 81). The DRR has the size of 501x501, and the point is supposed to be 
at the center of the image. I can't figure out how the projection works. I 
really wish the projection geometry were better documented.

When real CT data sets were used, the objects in the output DRRs appear to 
have been shifted toward the left-bottom corner of the images. I searched 
the emails that have been posted before. It appears someone has pointed out 
the problem before. However, I did not find any answers to the question. By 
the way, the IntensityBased2D3DRegistration.cxx example code does not work. 
I have posted the problem a couple of days ago.

Someone help me out please!

Jian Wu