Implementation of multidirectional moiré computerized tomography: multidirectional affine calibration.

To realize three-dimensional (3D) instantaneous diagnoses for flow fields, many multidirectional optical computerized tomographic (optical CT) techniques based on laser interferometry have been proposed. Projections from different directions of these tomographic systems are captured simultaneously to reconstruct the test field. These projections are independent from each other. However, due to the inevitable errors from installation and difference between optical elements, projections will be imaged with different distortion and located at different positions on the sensors. Therefore, a multidirectional calibration should be performed to remap these projections to a unified coordinate system before CT reconstruction. As far as we know, the multidirectional calibration problem for laser interferometric CT techniques has never been discussed in previous research. In this paper, a six-directional moiré tomographic system is designed. Considering the projection characteristics of moiré deflectometry, a multidirectional affine calibration method is proposed to determine the extrinsic and intrinsic parameters of tomographic projections. With the calibration results, projections can be remapped to the unified coordinate system and the 3D distributions of flow field can be reconstructed.