Basic Concepts

SScanSS is used to simulate the positioning of a strain scanning neutron diffractometer. The following concepts are essential when using the software.

Sample

The sample is a digitized model of the object which is being evaluated for strain.

Fiducial Points

Fiducial points are a rigid set of points on the sample that are used to determine the position and orientation of the sample within the instrument. The coordinates of the fiducial points, (in the same coordinate system as the sample model), are required by the software. The type of fiducial points used will depend on the sample and the measurement equipment available. For example if a sample model is generated by LASER scanning, stainless steel spheres, (ball bearings), could be glued to sample prior to scanning. The centres of the spheres could then be determined by fitting spheres to the scanned model or by probing the spheres in the same coordinate frame as the scanner.

Tip

Fiducial points should be rigidly mounted on the sample before digitizing the sample. The sample could move if the fiducials are mounted after digitization which would lead to errors in the simulation.

A minimum of three fiducial points are required which must not be placed along a line but randomly on the sample in positions that are visible/reachable from the measurement equipment when on the instrument. It is generally better to set up 5 to 7 points since using more that three points could lead to more robust and accurate position and orientation estimation, and also adds redundancy if some points are lost.

Sample with retro-reflective fiducials (left) laser tracker target holder (right)