Holistic multi-camera deflectometry (MultiDeflect)

几何光学计量实现快速，稳健，非接触和准确的3D形状测量。因此，在许多制造应用的质量控制中，它的应用是优先的。偏转法特别适合作为镜面的测量技术，如汽车车身和光学部件的清漆。偏转计使用显示区域上的特定图案，这些图案反射到物体表面，并由成像系统（如ccd摄像机）观察。相位测量偏转法（PMD）使用正弦条纹模式，产生一个独特的编码应用相移。通过使用光线追踪识别表面位置和局部坡度来评估被测表面的几何形状。从这种方法中产生了偏转测量的一些基本性质：1)位置和局部斜率是模糊的。通过引入先验知识或附加传感器来实现唯一性。ii)相对于位置而言，对局部斜率的敏感性明显更高。形状采集是通过在斜坡上积分获得的。这导致对系统校准的要求特别高，因为校准误差将通过此过程传播。该项目旨在充分利用大量的传感器信息和先验知识，以及各种解决歧义的方法，以改善系统校准，降低测量不确定度。这是通过对所有系统参数的整体处理来实现的，类似于用于相机自动校准的束调整。在文献中，通过在整体方法中引入额外的独立信息来调查校准和测量过程中准确性的改进，只有初步的研究已经提出。相机主要在摄影测量模型中处理，尽管无模型视觉射线校准能够为整体方法提供额外的信息。因此，拟议的项目设想了一个PMD装置的组装，该装置可以访问4个摄像机和一个用于确定参考点的距离传感器。以下子目标必须存档：i)考虑1 - 4个摄像头的整体优化程序的开发和鉴定；Ii)结合多相机技术和参考点知识解决模糊问题；Iii)通过在相机上附加应用视觉射线模型来改进优化。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，因为更有效地利用了可用的传感器信息。此外，还论证了通过附加传感器提高精度的局限性和可能性。

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.