Reflect on almost-parallel geometries
The easiest tomography setting is the following:
- Parallel beam
- Circular trajectory
- Rotation axis in the center, perpendicular to the incident beam
An "almost-parallel geometry" is a setting slightly deviating from above.
Here is an attempt to classify the deviation from this ideal setting, with an increasing difficulty.
Order 0
Rotation axis not in the center of the sample.
Order 1
Displacements of the rotation axis:
- Horizontal displacement
- Vertical displacement: helical scan
The rotation axis is still perpendicular to the beam.
The helical scan can be relatively easily handled by an intermediary conversion between the projections and sinograms.
Order 2
The rotation axis is not perpendicular to the beam anymore.
It is not clear whether this case should be handled natively by nabu
, or by an external tool like astra
.