[Camino-users] questions on reorient: shift in voxel count and identity addition to jacobian

[Alessandro Calamuneri]

I camino experts,
I am writing you because I would like to better understand how *reorient*
works on tensors. I have checked the source code, and two points are not
clear to me: first one is that, when using displacement field coming from
FSL fnirt command, there is a sistematic shifting on voxel position of half
unit; indeed you typed down

*double posX = (voxX+0.5)*CL_Initializer.voxelDims[0];*
*double posY = (voxY+0.5)*CL_Initializer.voxelDims[1];*
*double posZ = (voxZ+0.5)*CL_Initializer.voxelDims[2];*

Why does this shifting occur? Is it an fsl related issue?
The other question is coming from jacobian construction. Why do you add an
identity matrix to the Jacobian after getting directional derivatives of
displacement field?

Best Regards,

Alessandro
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