Impact of Stereo Camera Calibration to Object Accuracy in Multimedia Photogrammetry

Abstract

Camera calibration via bundle adjustment is a well-established standard procedure in single-medium photogrammetry. When using standard software and applying the collinearity equations in multimedia photogrammetry, the effects of refractive interfaces are compensated in an implicit form, hence by the usual parameters of interior orientation. This contribution analyses different calibration strategies for planar bundle-invariant interfaces. To evaluate the effects of implicitly modelling the refractive effects within bundle adjustment, synthetic error-free datasets are simulated. The behaviour of interior, exterior, and relative orientation parameters is analysed using synthetic datasets free of underwater imaging effects. A shift of the camera positions of 0.2% of the acquisition distance along the optical axis can be observed. The relative orientation of a stereo camera shows systematic effects when the angle of convergence varies. The stereo baseline increases by 1% at 25° convergence. Furthermore, the interface is set up at different distances to the camera. When the interface is at 50% distance assuming a parallel camera setup, the stereo baseline also increases by 1%. It becomes clear that in most cases the implicit modelling is not suitable for multimedia photogrammetry due to geometrical errors (scaling) and absolute positioning errors. Explicit modelling of the refractive interfaces is implemented into a bundle adjustment and is also used to analyse calibration parameters and deviations in object space. Real experiments show that it is difficult to separate the effects of implicit modelling, since other effects, such as poor image measurements, affect the final result. However, trends can be seen, and deviations are quantified.

An Efficient Solution to Ray Tracing Problems in Multimedia Photogrammetry for Flat Refractive Interfaces

“…All studies show that cameras facing orthogonally to the interface with a high percentage of water in the optical ray path, can well be calibrated applying the standard pinhole model with additional distortion parameters. This is congruent with other studies observing similar behavior (Kotowski 1988;Treibitz et al 2012;Shortis 2015;Kahmen et al 2020b). However, while Kang et al (2012) and Kahmen et al (2019) solely focus on this case, Sedlazeck and Koch (2012) and Hemmati and Rashtchi (2019) show that deviating from this optimum setup (i.e.…”

“…The results show a clear tendency towards an accuracy loss without explicit modeling, even for the orthogonal interface right in front of the camera. This finding in the orthogonal case contradicts other authors, such as Kotowski (1988), Shortis (2015) or Kahmen et al (2020b). This may be caused by the variable acquisition distance, which enforces distance-dependent distortions even more.…”

Monocular Photogrammetric System for 3D Reconstruction of Welds in Turbid Water

“…In Kahmen et al (2020), synthetic datasets are simulated to analyse the imperfect mathematical modelling of flat ports. If the optical refraction is explicitly modelled, as described by Kotowski (1987) and implemented in a universal approach by Mulsow (2010Mulsow ( , 2014, the interface parameters (thickness, refractive index) can be calibrated as well, as also shown in (Jordt-Sedlazeck and Koch 2012;Sedlazeck and Koch 2011) in the field of computer vision.…”

Bundle Adjustment With Polynomial Point-to-Camera Distance Dependent Corrections for Underwater Photogrammetry

“…Jordt-Sedlazeck & Koch (2012) introduce the non-single view point interpretation. While it is universally recognised that it would be preferable not to neglect the effect of refraction by properly modelling the phenomenon, it is difficult to quantify the improvement achieved over the implicit modelling approach in real cases (Kahmen et al, 2020). This is due to factors, such as water turbidity, back scatter induced by suspended particles, optical aberrations introduced by the water/air interface, which are not explicitly modelled in the proposed models.…”