Close-range Photogrammetric System Research Articles

A digital close range photogrammetric observation system for measuring soil surface morphology during ongoing rainfall

Soil erosion is a hydro-geomorphic process occurring over the earth’ surface. The observation of soil surface morphology during ongoing rainfall at fine spatial and temporal scales are critical for the study of soil erosion. A digital close range photogrammetric observation system based on wireless networking technology was explored and established in this study. Through wireless networking, multi-cameras were concurrently controlled, solving the problems of synchronous acquisition of underlying digital image, big data transmission and storage. Image sensors collected data in parallel based on network command, and noise on the images such as raindrops was eliminated based on the K-means clustering algorithm by serialization technology during data acquisition. After parallel preprocessing, high density 3D point clouds and digital elevation models (DEMs) were reconstructed. The evolution of soil surface topography was dynamically monitored by instantaneous image acquisition at different time intervals during ongoing rainfall. The results showed that the measurement precision of the established system could reach a sub-millimeter level with the minimum single measurement error being 0.0069 mm. The maximum error between check point coordinates generated by photogrammetry and those generated by a Total station was 5.7 mm on the horizontal axes and 9.6 mm on the vertical axis. The temporal and spatial resolutions of the observation system were 1 min and 2 mm, respectively. Compared with a runoff sediment collection method, the average relative error of the system for estimating soil loss was 5.63%, and the accuracy of single observation was up to 99.58%. The observation methods explored in our study provided a reliable way to monitor soil erosion processes, which was also helpful to analyze the role and influence mechanism of soil erosion in surface hydrological process.

The dynamic process of slope rill erosion analyzed with a digital close range photogrammetry observation system under laboratory conditions

As the main process of soil erosion in the Loess Plateau of China, rill erosion accounts for a large proportion of the total erosion on the slope. Quantifying the rill shape is crucial for studying the mechanisms and evolution of rill erosion. The objective of this study is to monitor the dynamic process of slope rill erosion using on a digital close range photogrammetry observation system during continuous rainfall. Artificial simulated rainfall experiments were conducted, and images were obtained at different time intervals. We used hydrological analysis and profile analysis tools in geographic information system (GIS) technology to extract rill networks and their main parameters to quantitatively describe the erosion processes of rill morphology. The results showed that (1) compared with the error from the traditional runoff sediment measurement method, the average error of the system for estimating soil loss was -7.06% and 1.05%, respectively, and the highest precision for a single observation was 99.46%; (2) the rill erosion process could be divided into several stages: raindrop splashing - eclipse - drop pit - erosion cave - rill cutting head - rill erosion - rill network; and (3) after rainfall lasted for 80min, the density and the degree of splitting increased continuously, and the maximum rill width and depth both showed fluctuating trends. The area of 7.5m to 9.5m away from the top of the surface was the most active area of rill erosion. The digital close range photogrammetric observation system can accurately obtain evolution information about rill erosion morphology during continuous rainfall, which provides a reference for future studies of soil erosion processes.

Multi-dimensional and multi-temporal motion estimation of a beam surface during dynamic testing using low-frame rate digital cameras

The combination of digital close-range photogrammetric systems and image processing techniques has been employed in structural health monitoring applications for more than 10 years. The use of off-the-shelf entry level digital single-lens reflex cameras has lately become a suitable choice even for applications requiring sub-millimetre- level precision especially when the involved devices need to be inexpensive. The drawback of such low-cost cameras is in the trade-off between spatial resolution, frame rate, and burst rate—at the highest available spatial resolution, a high frame rate is either not possible or it has a low burst rate. This may be problematic when monitoring a structural component during a dynamic/fatigue test. In order to estimate specimen motion in such a situation, this paper proposes an innovative sinusoidal fitting based on a least squares adjustment. This method simultaneously processes multiple bursts of data in order to synthetically increase the sampling frequency of the system. The input data for the adjustment comes from a full surface modelling procedure based on a newly proposed generalized 3D polynomial. The experimental results include a beam deformation test performed in a structures laboratory. The new sinusoidal fitting method effectively increased the system temporal resolution three-fold, which improved the precision of the derived parameters with up to two orders of magnitude. The root mean square error of the residuals were as good as 26 μm, and the one of the estimated amplitudes from the photogrammetric system versus a set of laser transducers used as control was as small as 43 μm.

Digital close range photogrammetry for the study of rill development at flume scale

Soil erosion is a continuous process of detachment, transportation, and deposition of soil particles. Obtaining accurate descriptions of soil surface topography is crucial for quantifying changes to the soil surface during erosion processes. The objective of this study was to develop an improved close-range photogrammetric technique to assess soil erosion under rainfall conditions. Based on high overlapping image acquisition, digital point cloud matching, digital elevation model (DEM) generation and soil erosion calculation, a digital close-range photogrammetric observation system was explored and established. The results showed that the established digital photogrammetric observation system could accurately calculate the digital point cloud from the underlying surface with a 2min time interval and a 1.5mm spatial resolution. In addition, based on the DEM generated from digital point clouds, the amount of soil erosion in different topographic positions within various time periods was calculated. The digital photogrammetric observation methods explored in our study provide a reliable way to monitor soil erosion processes, especially under rainfall conditions. This approach can accurately resolve the evolution of the underlying surface soil erosion, which is of great importance in understanding soil erosion mechanisms.

Three-dimensional imaging of hold baggage for airport security

Abstract. This study describes a cost-effective check-in baggage screening system, based on "on-belt tomosynthesis" (ObT) and close-range photogrammetry, that is designed to address the limitations of the most common system used, conventional projection radiography. The latter's limitations can lead to loss of information and an increase in baggage handling time, as baggage is manually searched or screened with more advanced systems. This project proposes a system that overcomes such limitations creating a cost-effective automated pseudo-3D imaging system, by combining x-ray and optical imaging to form digital tomograms. Tomographic reconstruction requires a knowledge of the change in geometry between multiple x-ray views of a common object. This is uniquely achieved using a close range photogrammetric system based on a small network of web-cameras. This paper presents the recent developments of the ObT system and describes recent findings of the photogrammetric system implementation. Based on these positive results, future work on the advancement of the ObT system as a cost-effective pseudo-3D imaging of hold baggage for airport security is proposed.

New method to calibrate and validate a high-resolution 3D scanner, based on photogrammetry

Abstract In the last years close-range photogrammetric scanning systems, are acquiring a larger market share. This is due to low-cost hardware, components and to new user-friendly software. The ultimate, photogrammetric 3D scanning systems are very accurate and precise because, of the high-resolution cameras (over 10 Mpixels) they are equipped of and, the more precise algorithms of their software. The calibration phase is the primary step for the development of a, precise photogrammetric scanner. Through a good calibration it is indeed, possible to eliminate optical aberration issues and to obtain precise and, accurate three-dimensional measurements. In this study a powerful, calibration method, named full-field calibration, was implemented to, obtain high-precision values, using an original three-dimensional, calibrator, developed so as to increase the performance of this type of, calibration. Prior to using any measurement or 3D scanning system, precision and, accuracy have to be assessed. In this study a robust validation method, for photogrammetric scanning systems has been proposed. The validation, procedure consisted in: (1) operator error analysis, (2) reproducibility, error-analysis, (3) control-system error analysis, (4) scanning system, error analysis., The measurements taken using the “control system” (certified equipment in, terms of precision and accuracy) were considered as “gold standard”. The, photogrammetric measurements, subsequently obtained by the scanning, system, were aligned to the “gold standard” using Procrustes, registration. The system error was expressed as the displacement between, these two sets of measurements.

SIMULATION OF CLOSE-RANGE PHOTOGRAMMETRIC SYSTEMS FOR INDUSTRIAL SURFACE INSPECTION

Abstract. Close-range photogrammetric measurement systems are increasingly used for high-precision surface inspection of car body parts. These measurement systems are based on an active light source, the projector, and one or more cameras. Many systems use a sequence of fringe projection, mostly a combination of the gray code and phase shift technique. Basically the quality of the measurement result depends on best possible positions of these sensors, which requires human expert knowledge and experience. But is it possible to use computer-based algorithms to find optimal measuring positions? Simulation processes are discovered as part of a research project aimed at the evaluation of the quality of measuring positions concerning to visibility, the attainable accuracy and realizable feature extraction. One approach is the simulation of the photogrammetric sensor using ray tracing techniques to create photorealistic pictures from the sensor cameras view. This image sequence could be processed with the evaluation software of the system manufacturer in order to calculate a three dimensional point cloud. Following an actual/target comparison should indicate differences that trace back to insufficient measuring positions. In this paper we show how to build up a virtual close range photogrammetric sensor using POV Ray, a free ray tracing software. After introducing the simulation concept, the design of a virtual close range photogrammetric sensor is presented. Based on practical examples of sampled scenes the potential of photorealistic ray tracing is shown. Finally the usability of this simulation approach is discussed.

ONE-STEP AND TWO-STEP CALIBRATION OF A PORTABLE PANORAMIC IMAGE MAPPING SYSTEM

Abstract. A Portable Panoramic Image Mapping System (PPIMS) is proposed for rapid acquisition of three-dimensional spatial information. By considering the convenience of use, cost, weight of equipment, precision, and power supply, the designed PPIMS is equipped with 6 circularly arranged cameras to capture panoramic images and a GPS receiver for positioning. The motivation for this design is to develop a hand-held Mobile Mapping System (MMS) for some difficult accessing areas by vehicle MMS, such as rugged terrains, forest areas, heavily damaged disaster areas, and crowed places etc. This PPIMS is in fact a GPS assisted close-range photogrammetric system. Compared with the traditional close-range photogrammetry, PPIMS can reduce the need of ground control points significantly. Under the condition of knowing the relative geometric relationships of the equipped sensors, the elements of exterior orientation of each captured image can be solved. However, the procedure of a system calibration should be done accurately to determine the relative geometric relationships of multi-cameras and the GPS antenna center, before the PPIMS can be applied for geo-referenced mapping. In this paper, both of one-step and two-step calibration procedures for PPIMS are performed to determine the lever-arm offsets and boresight angles among cameras and GPS. The performance of the one-step and two-step calibration is evaluated through the analysis of the experimental results. The comparison between these two calibration procedures was also conducted. The two-step calibration method outperforms the one-step calibration method in terms of calibration accuracy and operation convenience. We expect that the proposed two-step calibration procedure can also be applied to other platform-based MMSs.

Accuracy assessment of vehicles surface area measurement by means of statistical methods

This paper presents an assessment of the different methods and techniques for measuring a vehicle’s surface area, including a close-range photogrammetric system with calibrated digital cameras, a mid-range laser scanning system and an expeditious method based on a specific tape measurement. These methods are compared with respect to their task-specific accuracy related to the area measurement by means of statistical test for the detection of the significant results. An uncertainty evaluation of these techniques is performed using a standard device that was previously calibrated with a coordinate measuring machine. The assessment of the gathered data reveals a potential for reducing the time and cost associated with close-range photogrammetry for vehicle surface area measurement and digitisation.

Development of an Image Synchronous-Capturing Installation for a close-Range Photogrammetric System

This paper presents the design and implementation of an image-capturing device with the function to focus on multiple images synchronously. This installation is a key subassembly of a close-range photogrammetric system (CRP) which is a camera-based device for the development of 3D profiling of cloth appearance and/or human body. This image capturing system consists of a set of USB cameras with geometric design, a supporting programme and a personal computer. In order to enable the synchronous image capturing function of 8 cameras within the limited space, a USB camera with 5 million effective pixels was developed. A programme for simultaneous image capture and a database of captured images have been developed using Visual Basic 6.0 and DirectShow.

Development of a digital close-range photogrammetric bridge deflection measurement system

This paper introduces a new close-range photogrammetric bridge deflection measurement system that has high accuracy and efficiency, and can be conveniently used by engineers without help from professional surveyors. After a general description of a photogrammetric bridge deflection measurement system, four critical components of the system are addressed in detail: camera selection and settings; camera calibration; network control (reference system and scale); and camera placement. The system configuration is introduced and the system is verified through the laboratory and field tests.

Accurate 3D Target Positioning in Close Range Photogrammetry with Implicit Image Correction

Accurate three-dimensional (3D) target positioning is of great importance in many industrial applications. Although various methods for reconstructing 3D information from a set of images have been available in the literature, few of them pay enough attention to the indispensable procedures, such as target extraction from images and image correction having strong influences upon the 3D positioning accuracy. This article puts forward a high-precision ellipse center (target point) extraction method and a new image correction approach which has been integrated into the 3D reconstruction pipeline with a concise implicit model to accurately compensates for the image distortion. The methods are applied to a copyright-reserved close range photogrammetric system. Real measuring experiments and industrial applications have evidenced the proposed methods, which can significantly improve the 3D positioning accuracy.

Development of a Robust Photogrammetric Metrology System for Monitoring the Healing of Bedsores

AbstractA three‐camera close range photogrammetric system for robust and precise measurement of bedsores has been designed and constructed. MEDPHOS (MEDical PHOtogrammetric System) consists of three synchronised cameras with convergent optical axes. A light projector is fixed in the centre of the rig that holds the cameras. A special dot pattern is projected onto the surface to be measured, to compensate for the lack of natural texture on the wound surface. The proposed algorithm consists of the following steps: the cameras and projector are calibrated so that all interior and exterior parameters are known; tailored image segmentation procedures are developed and applied for the detection of the projected pattern dots from the uneven background of the images using morphologic operators; and watershed transformation is used to tackle the problem of overlapping pattern dots. To reduce the effects of non‐uniform illumination and specular reflection of light due to humidity (often the case with wounds), a homomorphic transformation is developed and applied to the images. After segmentation of the images, a connected‐component labelling procedure is used to establish the points for matching. The centroids of these components were precisely calculated. Intensity‐based image matching has been tested without yielding satisfactory results due to the significant deviation from the Lambertian reflection assumption used for solving the correspondence problem. This problem is reliably solved by developing a new algorithm based on geometric constraints that allow feature‐based matching and do not need approximate values of the location of the targets in the images. This robust three‐focal constraint is found to be very effective for matching provided the necessary conditions for the system configuration are met. Auxiliary photometric constraints together with the calibrated projector (which is treated like an active camera) also serve as additional sources of information for reducing the number of remaining ambiguities and checking the consistency of the results. Almost all of the required biometric information can be obtained rapidly, robustly and easily using MEDPHOS. Experimental results showed the effectiveness of the proposed technique.

Automated Processes in Digital Photogrammetric Calibration, Orientation, and Triangulation

Recent innovations in digital close-range photogrammetric systems for industrial applications have made possible a high level of automation within the 3D coordinate measurement process. This paper reviews innovations in automation for off-line vision metrology (VM) systems and discusses their operational impact. Concepts such as coded targets, exterior orientation devices, and robust solutions to the multi-image target point correspondence problem are illustrated through reference to a VM system capable of dimensional measurement accuracies of close to 1:200,000.

A Refinement to Automated Photogrammetry

As part of the development of an automated close-range photogrammetric measurement system, a small but valuable refinement has been made to the algorithm which is used to automatically place the f...

INDUSTRIAL PHOTOGRAMMETRY: NEW DEVELOPMENTS AND RECENT APPLICATIONS

AbstractOver the past decade, photogrammetry has been increasingly applied as a precise three dimensional measuring tool in industrial and engineering works. Analytical photogrammetry is now routinely employed in tasks of measurement as diverse as machine tool inspection and fixture checking, structural deformation monitoring, the provision of control databases to guide industrial robots and the measurement of structures in earth orbit. Traditional photogrammetric techniques and instrumentation are usually inappropriate for industrial work and the development of complete, fully integrated close range photogrammetric systems has recently gained considerable impetus. This paper details some of the significant new developments in industrial photogrammetry, with particular reference to technological advances in the Simultaneous Triangulation and Resection System (STARS) designed by Geodetic Services, Inc. for industrial photograininetry. Practical aspects of industrial measurement are also presented in a review of some of the varying tasks that GSI has carried out in recent years. Emphasis is placed on demonstrating the flexibility, accuracy, reliability and economy of photogrammetry, as well as the progress made in automating this measurement technique.

Stereometry in very close-range stereophotogrammetry with non-metric cameras for human movement analysis

In this paper a stereophotogrammetric algorithm based on a black-box approach to the modelling of object to image spaces relationship is proposed. The algorithm is well suited for ‘very close-range photogrammetry’, with respect to experiments in which the measurement field is 0.5 × 0.5 × 0.5 m or smaller, as in the analysis of a few or small body segments movements. The attainable accuracy is high, better than 0.1% of the observation distance. Non-professional and even different cameras can be used. Consequently an inexpensive experimental setup can be realized. A very simple, cheap and easily usable calibration object is needed. Computation time for the reconstruction of object-space co-ordinates of point body landmarks is one order of magnitude lower than in the case of the Direct Linear Transformation (DLT) (Abdel Aziz and Karara, Proceedings of the ASP/U1 Symposium on Close-Range Photogrammetry, pp. 1–18. American Society of Photogrammetry, 1971; Marzan and Karara, Proceedings of the Symposium on Close-Range Photogrammetric Systems, pp. 420–467. American Society of Photogrammetry, 1975). Computation time for calibration is two-fold in respect of the DLT. An example of application to the recording of the movements of the index finger with respect to the metacarpophalangeal joint is given.

A close-range photogrammetric system for 3-D measurements and perspective diagramming in biomechanics

Criteria considered in developing a close-range photogrammetric three-dimensional mapping system and its overall performance are discussed. The system consists of a stereophotographic capability of two cameras with synchronized shutters, a stereoplotting instrument with three-dimensional digitizing capability and a Calcomp plotter. Mapping of human knee-bones (femur and tibia) and perspective diagramming for various attitudes of one bone head with regard to the other are illustrated. The system works off-line with respect to the three principal components. The system is fully operational and is considered very efficient with regard to the current needs. Various possibilities are discussed.

A non-metric close range photogrammetric system for mapping geologic structures in mines : 9F, 4T, 21R. PHOTOGRAMMETRIC ENGNG AND REMOTE SENSING, V42, N5, 1976, P637–648

A non-metric close range photogrammetric system for mapping geologic structures in mines : 9F, 4T, 21R. PHOTOGRAMMETRIC ENGNG AND REMOTE SENSING, V42, N5, 1976, P637–648