Publications (without graduation papers)

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Bräuer-Burchardt, Christian; Munkelt, Christoph; Heinze, Matthias; Gebhart, Ingo; Kühmstedt, Peter; Notni, Gunther;
Underwater 3D measurements with advanced camera modelling. - In: Journal of photogrammetry, remote sensing and geoinformation science, ISSN 2512-2819, Bd. 90 (2022), 1, S. 55-67

A novel concept of camera modelling for underwater 3D measurements based on stereo camera utilisation is introduced. The geometrical description of the ray course subject to refraction in underwater cameras is presented under assumption of conditions, which are typically satisfied or can be achieved approximately. Possibilities of simplification are shown, which allow an approximation of the ray course by classical pinhole modelling. It is shown how the expected measurement errors can be estimated, as well as its influence on the expected 3D measurement result. Final processing of the 3D measurement data according to the requirements regarding accuracy is performed using several kinds of refinement. For example, calibration parameters can be refined, or systematic errors can be decreased by subsequent compensation by suitable error correction functions. Experimental data of simulations and real measurements obtained by two different underwater 3D scanners are presented and discussed. If inverse image magnification is larger than about one hundred, remaining errors caused by refraction effects can be usually neglected and the classical pinhole model can be used for stereo camera-based underwater 3D measurement systems.



https://doi.org/10.1007/s41064-022-00195-y
Dittrich, Paul-Gerald; Kraus, Daniel; Ehrhardt, Enrico; Henkel, Thomas; Notni, Gunther;
Multispectral imaging flow cytometry with spatially and spectrally resolving snapshot-mosaic cameras for the characterization and classification of bioparticles. - In: Micromachines, ISSN 2072-666X, Bd. 13 (2022), 2, 238, S. 1-12

https://doi.org/10.3390/mi13020238
Ramm, Roland; Heinze, Matthias; Kühmstedt, Peter; Christoph, Andreas; Heist, Stefan; Notni, Gunther;
Portable solution for high-resolution 3D and color texture on-site digitization of cultural heritage objects. - In: Journal of cultural heritage, ISSN 1296-2074, Bd. 53 (2022), S. 165-175

A peculiar characteristic of cultural heritage objects is their uniqueness. This results in an enormous importance for their preservation against aging, accidents, destruction etc. Although not replacing physical preservation, one way is the digitization of the objects in their current state by modern scanning technologies. This research describes a new method to combine 3D shape and color texture data acquired without contact to achieve high-resolution 3D representations. The method was basis of a portable 3D digitization system. The portable character allows its application on-site, which is essential for sensitive and non-transportable objects. A structured-light 3D sensor and a photo camera are used to capture the object from various overlapping perspectives. Then, the 3D shape and photographic data are processed and merged into a complete textured 3D model. Resolution and accuracy of the final model are in the range of 0.1 mm. Beyond preservation, the models can be used to make museum objects digitally available for experts or visitors worldwide e.g. in the form of online databases or virtual museums. A first utilization of the presented technology was realized with historic globes, especially with a Schöner globe dating from 1515 as highlight. The used method can be extended beyond RGB texture acquisition using multi-/hyperspectral sensors leading to an increased information content about the objects.



https://doi.org/10.1016/j.culher.2021.11.006
Junger, Christina; Fütterer, Richard; Rosenberger, Maik; Notni, Gunther;
Characterisation of a FPGA-based multi-view stereo system with linear measuring arrangement. - In: Measurement: sensors, ISSN 2665-9174, Bd. 18 (2021), 100322, insges. 4 S.

In recent years, stereoscopic image processing algorithms have gained importance for a variety of applications. To capture larger measurement volumes, multiple stereo systems are combined into a multi-view stereo system (MVS). To reduce the amount of data and the data rate, calculation steps close to the sensors are outsourced to field programmable gate arrays (FPGAs) as upstream computing units. In this paper a FPGA-based MVS system with linear camera arrangement and part overlapping field of view is presented. The system consists of four FPGA-based passive stereoscopic systems and a downstream processing unit (Zynq Ultrascale ZU9EG SoC). This synchronizes the pre-processing modules and receives the disparity maps via HDMI. A subsequent computing unit calculates a coherent 3d point cloud. Basic investigation of the system is shown to use this system for road damage detection in the future.



https://doi.org/10.1016/j.measen.2021.100322
Simmen, Katharina; Buch, Benjamin; Breitbarth, Andreas; Notni, Gunther;
Non-destructive inspection system for MAG welding processes by combining multimodal data. - In: Quantitative infrared thermography, Bd. 18 (2021), 1, S. 1-17

Welding processes are influenced by many parameters. By merging data to multimodal information from multichannel images and signals of various welding parameters, the correlation of these and their influence on weld seam imperfections are investigated. The application of a multispectral area camera array enables a new approach on non-destructive testing particularly supported by the passive thermography. The results show the different cooling behaviour of several welding imperfections, such as porosity, and present the relation between incorrect welding parameters and imperfections.



https://doi.org/10.1080/17686733.2019.1664812
Horn, Robin; Rosenberger, Maik; Notni, Gunther; Golomoz, Andrei; Fütterer, Richard; Dittrich, Paul-Gerald;
Investigation on chromatic aberrations and its potential for application in depth measurement. - In: Measurement: sensors, ISSN 2665-9174, Bd. 18 (2021), 100113, insges. 4 S.

Chromatic aberrations are mostly supressed in typical industrial lenses to ensure a well-defined colour image. Beside the main wavelengths which are recognizable for the human eye, multispectral cameras can sample with a more detailed chromatic (spectral) resolution. This leads to a partial wavelength depended unsharpness in the images. If the imaging system can be well defined out of these imperfections, a depth information can be calculated. In this paper the theoretical model as well as a method for the 3D-reconstruction out of different colour (spectral) channels will be discussed.



https://doi.org/10.1016/j.measen.2021.100113
Zhang, Yan; Müller, Steffen; Stephan, Benedict; Groß, Horst-Michael; Notni, Gunther;
Point cloud hand-object segmentation using multimodal imaging with thermal and color data for safe robotic object handover. - In: Sensors, ISSN 1424-8220, Bd. 21 (2021), 16, 5676, insges. 16 S.

https://doi.org/10.3390/s21165676
Zhang, Chen; Gebhart, Ingo; Kühmstedt, Peter; Rosenberger, Maik; Notni, Gunther;
Real-time multimodal 3D imaging system for remote estimation of vital signs. - In: Multimodal Sensing and Artificial Intelligence: Technologies and Applications II, (2021), S. 117850F-1-117850F-14

The contactless estimation of vital signs based on conventional color cameras and ambient light can be affected by motions of patients and changes in ambient light. In this work, a multimodal 3D imaging system with an irritation-free controlled illumination was developed in order to mitigate these both problems. In the developed system the real-time high-precision 3D imaging is combined with VIS-NIR multispectral imaging and thermal imaging. Based on 3D data and color images, an approach was proposed for the efficient compensation of head motions, and novel approaches based on 3D regions of interest were developed for the estimation of heart rate, oxygen saturation, respiration rate, and body temperature from NIR multispectral video data and thermal video data. A proof-of-concept for the developed imaging system and algorithms can be delivered with first experimental results.



https://doi.org/10.1117/12.2592660
Breitbarth, Andreas; Hake, Cornelius; Notni, Gunther;
Measurement accuracy and practical assessment of the lidar camera Intel RealSense L515. - In: Optical Measurement Systems for Industrial Inspection XII, (2021), S. 1178213-1-1178213-12

LiDAR technology is increasingly being used as an area-based 3D measurement method. In addition to high aspirations in terms of accuracy, speed and resolution, manufacturers of lidar cameras are competing to reduce size, weight and power consumption. As one of the most compact high-resolution systems, the Intel RealSense L515 has undergone extensive testing according to VDI/VDE Guideline 2634. In addition, tests were conducted with glossy or partially transparent surfaces (acrylic glass, carbon fiber material and aluminum) as well as with human skin. The latter shows the applicability for human-machine interactions. Both laboratory conditions and the influence of natural light were used as environmental conditions. A comparison of the results is given by the Intel RealSense D415 stereo camera system.



https://doi.org/10.1117/12.2592570
Munkelt, Christoph; Heinze, Matthias; Schindwolf, Simon; Heist, Stefan; Notni, Gunther;
Irritation-free optical 3D-based measurement of tidal volume. - In: Automated Visual Inspection and Machine Vision IV, (2021), S. 117870A-1-117870A-7

The measurement of breathing biomechanics, such as tidal volume, can be used to assess both the breathing performance and the respiratory health of individuals. State-of-the-art methods like spirometry or body plethysmography require a mouthpiece or facemask., which can be uncomfortable to the test person. As an alternative, we propose to use the change of the geometric shape of the subjects torso while breathing. By acquiring 3D point clouds of the person with a real-time near-infrared (NIR) 3D scanner, we measure those changes in a comfortable, irritation-free, and contact-free manner. Accordingly, two continuously measuring structured light 3D sensors, using a GOBO-based aperiodic sinusoidal pattern projector at a wavelength of 850 nm, simultaneously capture the upper front and side torso of the subject at a frame rate of 200 Hz. Both 3D scanners are calibrated and operated in a sensor network fashion, yielding a unified data stream within a global coordinate system. This results in increased coverage and reduced occlusion of the patient's body shape, enabling robust measurements even in the presence of loose clothing and varying body figure. We collected data from 16 healthy participants in an upright sitting position, wearing everyday clothing during the measurements. For reference, we simultaneously recorded spirometry readings. An algorithm ("OpTidal") tracks the volume of the subject's torso from the 3D data. Comparison whith the reference data shows high correlation and low mean error for the absolute tidal volume readings. As such, our method is a viable, safe, and accurate alternative to spirometry and plethysmography.



https://doi.org/10.1117/12.2592714