Combination Of Photogrammetry Research Articles

3D Laser Scanning and UAVs in cultural heritage: The case of Old Navarino castle in Pylos, Greece

The archaeological site of Palaiokastro (Old Navarino castle), is located in Messenia on the Coryphasium peninsula, at the southern end of the beach of Voidokoilia in the Navarino Bay, SW Peloponnese. Palaiokastro was built during Frankish rule of the Peloponnese, in the 13th century, over the classical Acropolis of Pylos.The aim of this study is the initial documentation of the current situation of the medieval castle of Palaiokastro applying innovative technology including terrestrial laser scanner (TLS) and unmanned aerial vehicles (UAVs). TLS and UAV photogrammetry have been used in an integrated design to rapidly facilitate the acquisition of the whole gate, eliminating all possible occlusions. TLS was exploited for the acquisition of the facades while the UAV was used to capture the top view of castle gate. The recent improvement of the post-processing algorithms provides us with the ability to implement fusion methods of TLS and UAV models and also deliver an accurate 3D model of the whole gate.The combination of photogrammetry from the UAV with the data of the terrestrial laser scanner was used in order to give us a multitude of products such as textured 3D model, orthophotos, 2D floor plans, elevations and sections which are necessary for the complete and accurate geometric documentation of the current situation of the Southwest gate of Palaiokastro Castle. The various products mentioned assist in the better management of the study data and identification of the different construction phases of the South Gate.

3D geometric survey of cultural heritage by UAV in inaccessible coastal or shallow aquatic environments

AbstractCultural heritage in coastal or shallow aquatic environments is often located in areas where access is difficult or where accurate survey and documentation may not always be possible with terrestrial or aquatic equipment. The combination of photogrammetry and unmanned aerial vehicles (UAVs) generates a range of possibilities across multiple sectors, including history, ethnography and cultural heritage studies. Additionally, these methods can be used to prospect new archaeological sites. This article presents three case studies that use UAV techniques and Structure from Motion and Multiview Stereo (SfM‐MVS) photogrammetry to conduct topographic and geometric registrations of archaeological, historical and ethnographic sites (some of which are classified as cultural heritage sites). These examples are located in coastal or shallow aquatic environments that are difficult to survey with traditional methods. The results show that it is possible to carry out detailed geometric registration and heritage prospection over large coastal or shallow aquatic environments using a low‐cost UAV. Furthermore, the results of this work show great advantages in terms of cost and quality, even in cases where the seabed is below a shallow water column. Other particularities of SfM‐MVS application in aquatic environments are discussed. From an interdisciplinary perspective, this methodology will offer new possibilities for the study, restoration and conservation of archaeological, historical and ethnographic monuments.

A Preliminary Study of 3D Vernacular Documentation for Conservation and Evaluation: A Case Study in Keraton Kasepuhan Cirebon

Despite the wealth of cultural heritage objects in Indonesia, some of which are considered UNESCO World Heritage sites, more documentation still needs to be done. One of the reasons behind this problem is that the documentation of complex cultural heritage objects is more complicated than most modern objects, which are often more simplistic. This preliminary study aimed to document vernacular heritage buildings in 3D to be used as a conservation and building management tool. The built digital model can then be used as a building assessment tool. The data acquisition method used in this study was a combination of photogrammetry and laser scanner technology. The building model was stored as BIM (IFC model) and then georeferenced before being converted to IndoorGML. The building elements’ information contained in the building model was retrieved as input to analyze the building. This research included analyses for building assessment, natural room temperature, natural lighting, and indoor space and relation. All results from the analysis were used as input to calculate the reliability value of the building using the AHP method. The case study for the heritage building was the house of Prince Arya Denda at Kasepuhan Palace, Cirebon, Indonesia.

Glacier Retreating Analysis on the Southeastern Tibetan Plateau via Multisource Remote Sensing Data

Accurate multitemporal glacier change investigations and analyses are lacking on the southeastern Tibetan Plateau (SETP). A combination of photogrammetry, optical remote sensing and synthetic aperture radar (SAR) datasets can accurately identify large-scale glaciers; In the present study, glaciers in three periods on the SETP (1970s, 2000, 2020) were identified from multisource remote sensing data based on a deep learning method and manual visual interpretation, and multitemporal glacial inventory data from relatively high-frequency source imagery. Totals of 11648, 12993, and 11875 glaciers were identified in the 1970s, 2000, and 2020, with total areas of 13372.08 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 11692.31 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and 10612.94 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The general distribution of SETP glaciers was identified to be typical of alpine glaciers dominated by small-sized glaciers. The average elevation of glaciers was approximately 5000 m; the slopes were mostly lower than 40°, and the main aspect was southeast, followed by south and southwest. The glaciers retreated from the 1970s to 2020, and a total glacier area of approximately 2759.14 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was degraded during this time, with an average annual melting rate of 0.45% yr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Rising summer temperatures may be the driving force behind the continuous decline in the glacier area. Overall, the results obtained in this study showed relatively low uncertainty involved in the identification of glaciers compared to some previous studies. The results can provide accurate glacier information for glacier monitoring and modeling studies on the SETP.

Combining Photogrammetry and Photometric Stereo to Achieve Precise and Complete 3D Reconstruction.

Image-based 3D reconstruction has been employed in industrial metrology for micro-measurements and quality control purposes. However, generating a highly-detailed and reliable 3D reconstruction of non-collaborative surfaces is still an open issue. In this paper, a method for generating an accurate 3D reconstruction of non-collaborative surfaces through a combination of photogrammetry and photometric stereo is presented. On one side, the geometric information derived with photogrammetry is used in areas where its 3D measurements are reliable. On the other hand, the high spatial resolution capability of photometric stereo is exploited to acquire a finely detailed topography of the surface. Finally, three different approaches are proposed to fuse both geometric information and high frequency details. The proposed method is tested on six different non-collaborative objects with different surface characteristics. To evaluate the accuracy of the proposed method, a comprehensive cloud-to-cloud comparison between reference data and 3D points derived from the proposed fusion methods is provided. The experiments demonstrated that, despite correcting global deformation up to an average RMSE of less than 0.1 mm, the proposed method recovers the surface topography at the same high resolution as the photometric stereo.

A COMBINATION OF ADVANCED PHOTOGRAMMETRY AND LASER TRIANGULATION TECHNIQUES (VIDEO LASER SCAN™) FOR THE FREE-FLYING 3D INSPECTION OF SUBSEA ASSETS

Abstract. Over the last years, High-Definition (HD) video cameras have made visual inspections of subsea assets more efficient and a source of massive and critical information. But in many cases, this visual information is incomplete without dimensions and geometry and can be biased by the wrong optical perspective, the lack of scale, or bad water clarity.This paper will describe the development of a new Technology, called Video Laser Scan™ (or VLS™), based on the combination of Photogrammetry and Laser Triangulation techniques, that provides additional Intelligence to such subsea inspections. In addition, we will highlight the innovation recently brought by Artificial Intelligence and 3D Holograms.

Vermiculations in painted caves: New inputs from laboratory experiments and field observations

Vermiculations are aggregates of small particles commonly found on cave walls. They are a major concern for the conservation of painted caves, as they can potentially alter valuable prehistoric cave paintings. A previous rheological study of fine sediment deposits on cave walls revealed that this material can undergo a solid-to-liquid transition triggered by variations in the chemical composition of the water film on the wall. Such a transition could occur at the origin of vermiculations by allowing the sediment to flow under low mechanical stress. In this work, we provide quantitative information on the conditions leading to this transition and show the importance of the chemical composition of the water film on the cave walls. A complete understanding of the phenomenon will, however, require more field information. This includes monitoring of the evolution of vermiculations, for which we have developed a dedicated observation protocol. Based on the combination of photogrammetry and a geographic information system we were able to precisely map the walls of the Hall of Bulls in Lascaux cave from past and future photographs. To better understand the vermiculation process, pictures need to be taken regularly, and the chemical composition of the thin water film covering cave walls needs to be analyzed with a similar time step. The correlation between the evolution of vermiculations, the humidification phases of the walls, temperature changes and the chemical monitoring of the water film should shed new light on conditions triggering vermiculations.

Evaluation of Unoccupied Aircraft System (UAS) Remote Sensing Reflectance Retrievals for Water Quality Monitoring in Coastal Waters

Unoccupied aircraft systems (UAS, or drones) equipped with off-the-shelf multispectral sensors originally designed for terrestrial applications can also be used to derive water quality properties in coastal waters. The at-sensor total radiance a UAS measured constitutes the sum of water-leaving radiance (LW) and incident radiance reflected off the sea surface into the detector’s field of view (LSR). LW is radiance that emanates from the water and contains a spectral shape and magnitude governed by optically active water constituents interacting with downwelling irradiance while LSR is independent of water constituents and is instead governed by a given sea-state surface reflecting light; a familiar example is sun glint. Failure to accurately account for LSR can significantly influence Rrs, resulting in inaccurate water quality estimates once algorithms are applied. The objective of this paper is to evaluate the efficacy of methods that remove LSR from total UAS radiance measurements in order to derive more accurate remotely sensed retrievals of scientifically valuable in-water constituents. UAS derived radiometric measurements are evaluated against in situ hyperspectral Rrs measurements to determine the best performing method of estimating and removing surface reflected light and derived water quality estimates. It is recommended to use a pixel-based approach that exploits the high absorption of water at NIR wavelengths to estimate and remove LSR. Multiple linear regressions applied to UAS derived Rrs measurements and in situ chlorophyll a and total suspended solid concentrations resulted in 37 and 9% relative error, respectively, which is comparable to coastal water quality algorithms found in the literature. Future research could account for the high resolution and multi-angular aspect of LSR by using a combination of photogrammetry and radiometry techniques. Management implications from this research include improved water quality monitoring of coastal and inland water bodies in order to effectively track trends, identify and mitigate pollution sources, and discern potential human health risks.

Kültürel Mirasın Etkileşimli Keşfi İçin Mobil Artırılmış Gerçeklik ve Web Tabanlı Görselleştirme Teknolojilerinin Kullanılması: Sfenks Heykeli Örneği

Kültürel mirasın korunması, dijital dokümantasyonu ve sürdürülebilir bir anlayışla gelecek nesillere aktarılması uluslararası toplumların önceliklerinden biri haline gelmiştir. Fotogrametri tekniği kültürel mirasın dijital dokümantasyonunda başarıyla kullanılmıştır. Fotogrametri, dijitalleştirme, 3 boyutlu (3B) modelleme, görselleştirme ve simülasyon alanındaki son gelişmeler, dijital kültürel mirasın daha geniş yelpazede erişilebilirliği için yeni fırsatlar sunmaktadır. Fotogrametri, artırılmış gerçeklik (AG) ve web tabanlı görselleştirmenin kombinasyonu, kültürel mirasın etkileşimli sunumu için büyük bir potansiyele sahiptir. Bu çalışmada, fotogrametrik modellere dayalı mobil AG ve web tabanlı görselleştirme uygulamaları için bir iş akışı geliştirerek kültürel miras bağlamında sanal, interaktif ve sürükleyici bir deneyim oluşturulması amaçlanmıştır. Önerilen iş akışı, Kütahya Arkeoloji Müzesi’nde sergilenen Sfenks Heykeline uygulanmıştır. Fotogrametrik yöntem ile elde edilen 3B model optimize edilerek, AG ve web tabanlı görselleştirme uygulamaları için hazırlanmıştır. Çalışmanın sonuçları, AG, web tabanlı görselleştirme ve fotogrametri sinerjisinin kültürel mirasın etkileşimli olarak sunumu için büyük bir imkân sağladığını doğrulamıştır. Çalışmada tanımlanan araştırma çizgileri daha kapsayıcı kültürel miras ortamları oluşturmak daha keyifli ve zenginleştirici turizm deneyimi sağlamak amacıyla yeni fırsatlar sunmaktadır.

DEVELOPMENT OF A FAN-SHAPED DISTANCE METER SYSTEM FOR MEASURING MOVING ROTOR BLADES – CONCEPT, PHOTOGRAMMETRIC ORIENTATION AND FIRST RESULTS

Abstract. For wind turbines, the actual deformation of the rotor blades during operation is of great interest to manufacturers. Photogrammetry and laser scanning are suitable for contactless measurement. The torsion of the rotor blade is of major interest and should be determined with an accuracy of less than 1°. This requires a high precision in the recording distance. The combination of photogrammetry and laser scanning thus enables the acquisition of the relevant data. The nacelle movement is photogrammetrically measured. To measure the torsion, laser scanners in 1D mode are used. A further development of the measuring scenario is a novel fan-shaped distance meter system, presented in this contribution. It consists of four distance measuring units of a Z+F Imager 5006 laser scanner, whose laser beams span a plane in object space. The distance measuring units provide synchronous range measurements. For the calculation of 3D coordinates, their relative orientation is required. Two photogrammetric approaches are presented in this paper. In the first method, the meter system is moved relative to the testfield. The data acquisition and evaluation is complex. In the second method, a stereo camera is built onto the meter system so that 3D coordinates can be measured directly. This method allows a fast data acquisition and evaluation for system calibration. The realization on a real wind turbine is possible. This contribution discusses challenges and advantages of measuring the rotor blades during operation and presents the realisation of the novel meter system and the determination of the relative orientation. The new meter system makes it possible to measure the torsion during operation of the wind turbines without any targeting with required accuracy.

UAV-BASED PHOTOGRAMMETRY FOR ARCHAEOLOGICAL HERITAGE SITE SURVEY AND 3D MODELING OF THE SARDUS PATER TEMPLE (ITALY)

Abstract. Despite the high standard guaranteed by 3D scanning technology, image based modeling establishes the most widely used technique for surface reconstruction, being a cheaper and more portable approach. The strong increase in the use of Unmanned Aerial Vehicles (UAVs), is increasingly affirming and consolidating over the years. Being more cheap and portable than the active sensors approach, the combination of photogrammetry and drones is widely used for different applications both for large scale mapping and for documentation of architecture and archaeological heritage. UAV based photogrammetry allows for rapid accurate mapping and three-dimensional modelling. Over the last two decades, the study of archaeological sites have benefited from the constant evolution of sensor-based surveying techniques, finding effective application for purely visualization purposes or for the extraction of metric data. The Punic-Roman temple "Sardus Pater Babai" in southern Sardinia (Italy), has been the subject of a massive anastylosis. The close-range photogrammetry technique, exploiting the images produced by a UAV consumer and the GNSS system data, has allowed the creation of metrically correct 2D and 3D models useful also for an effective visualization of the information. A series of ortho-images has been extracted in order to represent plan, elevations and cross-sections of the monument.

Methodology for diagnosing crack patterns in masonry structures using photogrammetry and distinct element modeling

Understanding the causes of damages on existing structures can augment preservation, renovation, and rehabilitation efforts. The aim of this work is to outline a method for diagnosing the most probable causes of cracks on existing structures using a combination of photogrammetry and distinct element modeling (DEM). Five experimental, masonry walls were constructed and cracked; the state of the wall before and after cracking was recorded using photogrammetry. Using distinct element modeling, each test wall was subjected to a variety of loading conditions including the same load case which was used to crack the wall during experimental testing. The crack patterns in the simulations were compared to the experimental crack patterns using a combined qualitative and quantitative method. The simulation which most closely reflected the existing damage patterns was selected as the most probable cause of the damages. For each of the test walls, the real simulated load had the closest fractional distance to the existing damage patterns captured by photogrammetry. This method was then applied to diagnose possible causes of cracking on a foundation wall in the Baptistery of San Giovani in Florence, Italy.

Decadal‐scale dynamics of an Amazonian mangrove caused by climate and sea level changes: Inferences from spatial–temporal analysis and digital elevation models

AbstractSea level rise and climate change are major forces driving wetland dynamics. The northern Brazilian coast has one of the largest continuous mangrove areas on Earth, with the mangroves from the Bragança Peninsula, in eastern Amazonia, being the most representative ones. These mangroves have migrated into higher tidal flats over recent years. We analyzed spatial–temporal changes of vegetation units adapted to different physical–chemical conditions along the Bragança Peninsula in order to decipher possible causes responsible for such recent mangrove dynamics. The investigation was based on time series analysis of a 33‐year (1984–2017) database consisting of satellite and drone images. These data were combined with digital elevation models based on topographical data obtained by photogrammetry, theodolite and hydrotopographic devices. During this time frame, mangroves invaded 2.7 km2 of inner tidal flats, which is compatible with a rise in relative sea level (RSL) and with a rainfall decreasing. Such topography‐dependent dynamic suggests that an increased frequency of tidal inundation decreased porewater salinity and caused mangroves to expand into topographically higher grounds. However, the study area contains small basins, that are less affected by tidal inundation, and Avicennia trees are dying in these locations due to increased porewater salinity, probably caused by a decreased rainfall. We propose that climate and RSL are responsible for driving the death of mangroves in the study area, and their migration into the topographically highest tidal flats. Assuming a RSL rise of 5 mm/yr under stable rainfall, or a RSL rise of 3 mm/yr accompanied by decreased rainfall, it is projected that mangrove areas will expand by 2.93 or 1.35 km2, respectively, by the end of this century. The combination of photogrammetry with theodolite/hydrotopographic surveying proved to be an efficient and innovative process for monitoring and evaluating the impacts of global changes on mangroves. © 2018 John Wiley &amp; Sons, Ltd.

Digitization of the Cultural Heritage of Slovakia. Combining of Lidar Data and Photogrammetry

&#x0D; During the years 2013-2016 a great number of buildings (medieval castles, churches and other monuments) in Slovakia were digitized. STUDIO 727 was the main provider of these digitalization works. &#x0D; The subject of our investigation was the most significant Slovakian historical objects. Within the digitalization project we have created 3D models of the most important Slovakian monuments, as e.g. Bojnice castle, gothic church in Spišský Štvrtok or Devin castle, where there are also artifacts from Roman period, La Tène era and Middle Ages. &#x0D; The aim of the project was to identify current technological possibilities for the creation of virtual presentations of real spaces. During the creation of the 3D models we used a combination of Photogrammetry and 3D space scanning by laser scanner LIDAR (Leica brand). Final modification of laser outputs was made using Cyclone software. Post processing was done with Capture Reality, Autodesk Maya and MeshLab software. 2D documentation was made using AutoCAD. &#x0D; The purpose of documentation was to capture the appearance of historical buildings and historical building technologies, to keep culture heritage for next generation. Some monuments, which have been falling apart progressively, were documented. The documentation created will contribute to culture heritage publicity and provides documentation for the future renovation of these particular monuments. The Entry of this project was the process of creating 3D virtual models and 2D documentation.&#x0D; Contribution was created thanks to EU project, within the Operational program Informatization of society. Project was supported by The Ministry of Culture of Slovak Republic and Government Office of Slovak Republic. &#x0D;

Shear load testing of damaged hollow‐core slabs

As a result of poor‐quality sealing, moisture and deicing agents had penetrated into the prestressed hollow‐core slabs of the top floor of an uncovered parking deck. The slabs showed especially severe chloride‐induced damage in the support regions near the joints. Owing to the damage, the theoretical shear capacity according to the technical approval of these slabs was highly questionable. The influence of the damage on the shear capacity of the slabs with different levels of damage was determined with the help of an experimental in situ loading test. Based on the results, the number of slabs that had to be replaced or repaired could be reduced. For the experimental investigation of the shear capacity of the hollow‐core slabs, a combination of photogrammetry, acoustic emission analysis, and curvature measurement for each section was used to determine the initial shear damage on a very low level during the test. The comparison of the results of the different measuring techniques allowed the damage processes to be clearly identified and significantly increased the quality of information about the structural condition of the slabs during the experimental investigation.

Photogrammetric Scanning and Applications in Medicine

Creating 3D models automatically from photographs is a relatively new technology. This sort of 3D scanning is based on the principles of photogrammetry, similar in methodology to panoramic photography; the photos are taken of one object and from different positions of camera in order to replicate the object. Paper approaches different typical anatomic surfaces by photogrammetric scanning and 3D reconstruction. Documented surfaces include anatomic surfaces like foot, upper body, head, and ear. The aim is to give users recommendations, which body part is suited best for this type of scanning, or even if a combination of photogrammetry and another 3D scanning technique is advisable. Comments like possible medical applications, quality of the results, required equipment and occurring problems are to be considered.

Mapping of a river using close range photogrammetry technique and unmanned aerial vehicle system

Photogrammetry is a technique that can be used to record the information of any feature without direct contact. Nowadays, a combination of photogrammetry and Unmanned Aerial Vehicle (UAV) systems is widely used for various applications, especially for large scale mapping. UAV systems offer several advantages in terms of cost and image resolution compared to terrestrial photogrammetry and remote sensing system. Therefore, a combination of photogrammetry and UAV created a new term which is UAV photogrammetry. The aim of this study is to investigate the ability of a UAV system to map a river at very close distance. A digital camera is attached to the Hexacopter UAV and it is flown at 2 m above the ground surface to produce aerial photos. Then, the aerial photos are processed to create two photogrammetric products as output. These are mosaicked orthophoto and digital image. Both products are assessed (RSME). The RSME of X and Y coordinates are ±0.009 m and ±0.033 m respectively. As a conclusion, photogrammetry and the UAV system offer a reliable accuracy for mapping a river model and advantages in term of cost-efficient, high ground resolution and rapid data acquisition.

Positioning sensor by combining photogrammetry, optical projection and a virtual camera model

A novel, low cost, non-contact measurement technique is proposed to realize an optical positioning sensor that enables real-time measurement of a small lightweight module's location. The technique is based on a combination of photogrammetry, optical projection and a virtual camera model. The module generates an optical pattern that is observable on the surrounding walls, photogrammetry is used to track the motion of the projected optical pattern, and this indirectly allows the motion of the module to be tracked. This is done by treating the module as a virtual pinhole camera, generating a virtual image that carries the angular characteristics of the optical pattern. Images of the projected optical pattern on the walls taken by cameras around the room, together with the virtual image, are then processed through a photogrammetry-based bundle adjustment. This results in a position and orientation estimate of all cameras, including the virtual pinhole camera. The position and orientation of the virtual camera is therefore also the position and orientation of the module. Both experiment and optical ray-trace simulations are performed to validate the proposed technique. Experimental agreement of 3 parts in 104 was obtained by translating the module over 0.9 m. The incorporation of the virtual camera model is innovative, leads to a simple solution, and is more robust than the previously published approach.

Complementing TLS Point Clouds by Dense Image Matching

The complementation of terrestrial laser scanning (TLS) by photogrammetric acquisition techniques enables the exploitation of two different measurement principles. TLS with distance measurements can be used for acquiring large-scale point clouds at medium range distances, while image-based surface reconstruction methods enable flexible acquisition with high precision at short distances. Within this paper, an automatic procedure for the combination of photogrammetry and laser scanning is presented. Synthetic images derived from the laser scanning point clouds are used together with camera images in a common Structure-from-Motion (SfM) process. This enables an automatic registration of multiple laser scans. Furthermore, surface information can also be derived from the imagery using dense image matching methods. While the laser scanning data provides the missing scale information, the imagery can complement the dataset to fill gaps, occlusions or to resolve small details. Consequently, large datasets can be connected by registering imagery and laser scans.

Using Optical Projection in Close-range Photogrammetry for 6DOF Sensor Positioning

A novel, low cost, non-contact, six degrees of freedom (DOF) measurement technique is proposed that enables real-time measurement of a small lightweight module’s location. Straight forward applications of the proposed technique include robot calibration by installing the module to the end effector of a robot arm, and head-tracking in a typical virtual reality environment by attaching the module to a human head. The technique is based on a combination of photogrammetry and optical pattern projection. The module generates an optical pattern that is observable on the surrounding walls, and photogrammetry is used to measure the absolute coordinates of features in the projected optical pattern with respect to a defined global coordinate system. By combining these absolute coordinates with the known angular information of the optical projection beams, a minimization algorithm can be used to extract the absolute coordinates and angular orientation of the module itself. Experimental agreement of 1 to 5 parts in 103 was obtained by translating the module over 0.9 m and by rotating it through 60°. Numerical simulations were conducted to demonstrate that optimum design of the projected pattern gives a lower associated measurement uncertainty than is possible by direct photogrammetric measurement with traditional tie points. This paper documents the proof of principle and describes how the measurement can be further improved.