I rigidly registered two images using the Landmark-Based registration. I chose “Affine Registration” as the Registration Type and “Rigid” as Registration Mode. The resulting registration looks good, so I tried to export the transform for usage in other programs by choosing “save”.
However, the resulting files (I tested both .txt and .mat) have a slightly different transformation matrix than what I get when I look at the transform in slicer (Right click on the transformation->Edit properties).
Slicer’s GUI shows:
In the text file, I have:
#Insight Transform File V1.0
Parameters: 0.9989776251379424 0.04090843080016693 -0.01924070589205142 -0.04089969593416781 0.9991628979972874 0.0008474303244814285 0.01925926650340259 -0.00005962491247667927 0.9998145213481452 -4.374452815811267 -95.00156325189849 424.48027296194584
FixedParameters: 0 0 0
I expect the first 9 parameters to be the rotation and the last three to be the translation. Some values are not the same (see for example the x-value of the translation which changes from -7 mm to -4 mm)
When applying the exported transform in blender or paraview (to the segmented meshes which I get from the original images) I thus get a small offset in position and rotation.
Tested with Slicer Version 4.8.0 r26489. Is this a bug, or am I interpreting the transform wrong in the other programs?