Holistic multi-camera deflectometry (MultiDeflect)

几何光学计量能够实现快速、稳健、非接触和精确的3D形状测量。因此，它的应用是优先在许多制造应用的质量控制。偏折法特别适合作为镜面的测量技术，如涂漆车身和光学元件。偏折法使用显示区域上的特定图案，这些图案在物体表面上反射并由成像系统（诸如CCD相机）观察。相位测量偏折术（PMD）使用正弦条纹图案通过施加相移来产生唯一编码。通过使用光线跟踪识别表面位置和局部斜率来评估测试表面的几何形状。从这种方法中产生了偏转测量的一些基本性质：i）位置和局部斜率是不明确的。通过引入先验知识或额外的传感器来实现均匀性。ii）与位置相比，相对于局部斜率的灵敏度显著更高。通过在斜率上积分来获得形状采集。这导致对系统校准的特别高的要求，因为校准误差将通过该过程传播。该项目旨在充分利用大量的传感器信息和先验知识，以及各种方法来解决模糊度，以提高系统的校准和降低测量不确定度。这是接近的所有系统参数的整体处理类似于光束调整用于自动校准的相机。在文献中，只有初步的研究，调查在校准和测量过程中引入额外的独立信息，在一个整体的方法来提高精度。相机主要在摄影测量模型中进行处理，尽管无模型视觉射线校准能够为整体方法提供更多信息。因此，拟议项目设想组装一个PMD装置，可使用4个摄像头和一个距离传感器来确定参考点。以下子目标必须存档：i）考虑1至4个摄像机的整体优化程序的开发和鉴定; ii）通过结合多摄像机技术和参考点的知识来解决模糊性; iii）通过将视觉射线模型附加应用于摄像机来改进优化。这里要开发的程序适用于现有的PMD系统，以减少其测量不确定性和测量和校准所需的时间，由于更有效地利用可用的传感器信息。此外，限制和可能性，提高精度的额外的传感器被证明。

Geometric-optical metrology enables fast, robust, non-contact and accurate 3D shape measurement. Hence, its application is preferential in quality control of many manufacturing applications. Deflectometry is particularly suited as a measurement technique for specular surfaces such as varnished car bodies and optical components. Deflectometry uses specific patterns on a display area which are reflected on the object surface and observed by an imaging system as such as a CCD-camera. Phase Measuring Deflectometry (PMD) uses sinusoidal fringe patterns to yield a unique coding by applying phase shifting. The geometry of the surface under test is assessed by identifying surface positions and local slopes using ray tracing. From this approach some fundamental properties of deflectometry arise: i) Position and local slope are ambiguous. Uniqueness is achieved by introducing prior knowledge or additional sensors. ii) The sensitivity with respect to the local slope is significantly higher compared to the position. Shape acquisition is gained by integrating over the slopes. This leads to particularly high demands on the system calibration since calibration errors will propagate through this process. The project aims at making best use of the huge amount of sensor information and prior knowledge as well as various methods to solve ambiguities in order to improve the system calibration and to lower the measurement uncertainty. This is approached by holistic treatment of all system parameters analogous to the Bundle Adjustment used for auto-calibration of cameras. In the literature, only rudimentary studies on investigating the improvement of the accuracy during calibration and measurement by introducing additional independent information in a holistic approach have been presented yet. Cameras were mainly treated in the photogrammetric model although the model-free Vision Ray Calibration is capable of providing additional information to the holistic approach. The proposed project therefore envisages the assembly of a PMD setup with access to 4 cameras and a distance sensor for the determination of a reference point. The following sub goals must be archived: i) Development and qualification of holistic optimization procedures considering 1 to 4 cameras; ii) solving the ambiguity by combining the multi camera technique and the knowledge of a reference point; iii) improved optimization by additional application of the vision ray model to the cameras. The procedures to be developed here are applicable to existing PMD systems to reduce their measurement uncertainty and the time required for measurement and calibration due to a more effective usage of available sensor information. Furthermore, confinements and possibilities for improving the accuracy by additional sensors are demonstrated.