Beam

Each TomoDetector provides a pixel size related to the sample (sample_pixel_size).

This pixel size can ever be provided by the user or be automatically computed.

A sample_pixel_size_mode property is provided to select one of this modes.

Software architecture

A TomoDetector is aware of the existance of a lot of objects.

This objects are used to compute the auto pixel size.

User pixel size

A user pixel size can be set manually to each detectors.

For that:

• sample_pixel_size_mode have to be setup to USER
• And a value can be defined for user_sample_pixel_size

In this case sample_pixel_size with expose the user pixel size.

In this mode, the pixel size remains the same for any changes on sample/source/detector/optics.

Only a change of the binning of the detector will update it.

Auto pixel size

In this mode the sample pixel size is automatically computed based the following modelization.

For that the following constants have to be tuned properly:

• sx0: the location of the focal position in the sample axis
  • This can be setup by defining z1 (tomo.sample_stage.source_distance)
• cx0: the location of the focal position in the detector axis
  • This can be setup by defining z1+z2 (tomodetector.source_distance)
  • This can be setup by defining z2 (tomodetector.sample_detector_distance)
  • The detector offset related to the holder (TomoDetectors) could have to be fine tuned

The pixel size is computed based on the detector pixel size and binning, plus the optic magnification plus a ratio based on the source/sample/detector distances (z1, z2).

Finally sample_pixel_size_mode have to be set to AUTO, which switch sample_pixel_size to the value of auto_sample_pixel_size.

In this mode, the pixel size is updated automatically during:

• sample axis displacements (event based)
• detector axis displacements (event based)
• tomo config parameter change change (event based)
• optic magnification change (event based)
• Lima detector changes (not event based)

Beam tracker

For conic beam, the focal point and the detector are not necesserely orthogonal to the translation of the sample stage.

This geometry is modelized in order to follow the beam when the sample stange move.

Beam tracker

The bean tracker is an optional device which can be setup.

For now it can be setup with sy_angle, sz_angle in radian.

The focal_position is a sample stage parameter which have to be setup independently.

Tracked axis

A tracked_translation_x axis can be exposed from the TomoConfig. It is a copy of translation_x, but when a motion is requested, the other translations will be moved together (based on the beam tracked configuration) to follow the beam.

Detector center

The detector center is a parameter from the tomo sample stage. It identifies the location of the detector at the sample stage coordinates.

This detector center is mandatory to display the image properly in Daiquiri and to guess the location of the axis rotation. That is why this information is exposed as scan metadata.

In the case of a conic beam, the value of the detector center depends on the location of the sample stage in X, and follow this equation. The beam tracker is responsible of the update of the value.

For non-conic beam or beamline which does not use sample stage translation in X, this value can be set manually.