Close Range Photogrammetry Technique Research Articles

Analysis Of 3-D Building Modeling Using Photogrammetric Software: Agisoft Metashape And Micmac

In constructing three-dimensional models, photogrammetry techniques, particularly close-range photogrammetry techniques, are growing and becoming an alternative, specifically for architectural and historical site modeling. Because they are less costly, simpler, and quicker to complete while producing positive results, there is a great number of photogrammetry software. Still, it is difficult to determine which application provides the best measurement results because user expectations vary. It is necessary to conduct geometric precision and visualization analyses to assess the software’s output. For this experiment, 3D models of a building were created using Agisoft Metashape and MicMac. The geometric accuracy calculated by Agisoft Metashape has RMSE values of x=0.025 m, y=0.037 m, and z=0.021 m. RMSE values for the MicMac are x=0.066 m, y=0.129 m, and z=0.118 m. Visually, the Agisoft Metashape-created three-dimensional model offers superior visual results and fewer connection points than the MicMac GUI. On a three-dimensional building model processed with Agisoft Metashape, the generated cloud-to-cloud distance is comparable to the distance between the reference point cloud. Except for the building’s rear, the distance between clouds using the MicMac is nearly identical to that of the reference point cloud.

ANALYSIS OF TWO-OPTION INTEGRATION OF UNMANNED AERIAL VEHICLE AND TERRESTRIAL LASER SCANNING DATA FOR HISTORICAL ARCHITECTURE INVENTORY

The 3D reconstruction of historical and cultural heritage monuments is a procedure recommended by the UNESCO World Heritage Institution since 1985. It is crucial when conserving monuments and creating digital twins. Current 3D reconstruction techniques using digital images and terrestrial laser scanning (TLS) data are considered as cost-effective and efficient methods for the production of high-quality digital 3D models. In the presented study, laser scanning and close-range photogrammetry techniques and images taken by a low-cost unmanned aerial vehicle (UAV) were applied to quickly and completely acquire the point cloud and texture of a historic church in Poland. The aim of this study was to evaluate two options for integrating TLS and UAV data, using ground control points (GCP) measured by two independent techniques: tachymetry and laser scanning. The study shows that the 3D model created based on ground control points acquired by the laser scanning technique has a mean square error RMSEXYZ = 2.5 cm on the check points. The result obtained is not much larger than the second variant of data integration, for which RMSEXYZ = 1.7 cm. Thus, the TLS method was positively evaluated as a GCP measurement technique for the integration of UAV and TLS data and the creation of cartometric 3D models of religious buildings.

Nondestructive deformation measurements and crack assessment of concrete structure using close-range photogrammetry

Reliable measurement of deformations and crack assessment of concrete structural elements under loading is essential for evaluating the performance and durability of these elements. Traditionally, structural elements are monitored under loading with strain gauges, deflectometer, and data acquisition systems. Limited studies have investigated the potential of close-range photogrammetry and three-dimensional (3D) modeling in analyzing deformations, internal stresses/strains, and crack propagation. This research proposes an innovative four-phase testing method to develop 3D models of the concrete beam with close-range photogrammetry and image processing techniques. The proposed method entails the capabilities of analyzing deformations, internal stresses/strains, and monitoring crack propagation. The main phases of the proposed method are as follows: 1) preparing the test setups, beam preparation, photogrammetry preparation, and surveying preparation; 2) testing the beam under loading while recording deformation data, collecting high-resolution images, and conducting ground-controlled surveying from nine points around the beam; 3) performing photogrammetric processing of the images to generate a textured 3D model of the beam; and 4) comparing the results from both the 3D model and the direct measurements. For triangulation accuracy, the overall RMSE of the generated model is 4.974 mm. While for product accuracy, the RMSE is 9.303 mm. Moreover, the RMSE for deformations is 0.115 mm, indicating acceptable accuracy of measurements through the model. In addition, a photogrammetric-based deformation model can be generated for the beam surface, and cracks area, length, and width are efficiently extracted and monitored.

Preliminary assessment of joint roughness coefficient of rock slope using close-range photogrammetry technique

Rock shear strength can be estimated using the Barton–Bandis model, which relies on the joint roughness coefficient (JRC). The Barton comb profilometer is widely used in the field. However, it requires much labor. It is also difficult to access and potentially dangerous. As far as we know, no comprehensive work is dedicated to determining the JRC of the rock block sample using the image analysis technique. The JRC measurement results are compared with the manual Barton comb profilometer results to determine the reliability of the close-range photogrammetry (CRP) technique. This photogrammetry technique is applied to measure the JRC of the rock slope in the study area. Using the CRP method, a drone (DJI Phantom 4 Pro) captures a high-resolution image of the rock slope. The JRC of the rock slope is digitized through image processing to create a three-dimensional model comprising four quality ratings: low, medium, high, and ultrahigh. The ultrahigh quality has the most accurate measurement among all the quality ratings. It has a 0% error compared with the actual measurement using the Barton comb, whereas low, medium, and high qualities have 15.54%, 9.46%, and 2.7% errors, respectively. However, the medium quality is the most efficient because it can produce a reliable JRC measurement within a short period and can be used for fieldwork.

The construction of a street never opened to traffic. The extraordinary discovery of pavement engineering in vicolo dei Balconi of Pompeii

A significant portion not yet investigated in the Regio V of the ancient city of Pompeii is currently the subject of the most remarkable excavation in the post-World War II period. These activities relate to a triangular area, the so-called “wedge”, which is placed between the houses of Nozze d'Argento and Marco Lucrezio Frontone. Besides the astonishment and scientific emotions resulting from the finding of magnificent frescoed and well preserved thermopolium, dwellings and balconies, also a feeling of extreme interest in the pavement engineering arose due to a further one of a kind discovery. The Somma-Vesuvium volcanic eruption of 79 AD buried a narrow alley, i.e. vicolo dei Balconi, during the construction of its stone pavement, in which the laying of compact lava stone flags was interrupted about halfway from north to south. The eruption and the following superimposition of lapilli, ash and pumice blankets has therefore maintained in a state of perfect documental conservation the whole area, preserving the new laid flagstones still showing the original surface finishing and the preparatory subgrade. Thus, this historical and archeological source becomes a priceless engineering evidence describing some of the design and construction techniques used by the Romans at Pompeii. The excavated area has been analyzed following a cross-disciplinary approach, adopting several minimally intrusive or non-destructive techniques and instruments belonging to different branches of science to capture some specific aspects. Specifically, the alley has been initially surveyed with a terrestrial laser scanner (TLS) device to build an accurate layout model of the worksite. Although the TLS survey provided an invaluable source of information for the street structures documentation, specific stone paving elements were also analyzed using close range photogrammetry techniques and their friction properties have been measured exploiting the potential of a modern road engineering device, i.e. a skid resistance tester, also known as the British pendulum tester (BPT). The consistency analysis of the subgrade structure and homogeneity in the unpaved section involved the use of two dynamic procedures, i.e. a penetrometric (dynamic cone penetrometer - DCP) and a deflectometric (light weight deflectometer - LWD) test. Besides, some design and urban planning considerations have been drawn from the analysis of the relationships between the finished structures and the pavement construction site according to the lines of the existing curbs, the thresholds of access to the dwellings and the placement of enigmatic prismatic blocks arranged in trenches, probably intended as a useful target points for the stonemasons or temporary pedestrian passage. In a wider reading a succession of paving works (and not repaving) using stone elements in this part of the city starting from the Cardo via del Vesuvio (from west to east) is recognizable.

Three-Dimensional Human Head Reconstruction Using Smartphone-Based Close-Range Video Photogrammetry

Creation of head 3D models from videos or pictures of the head by using close-range photogrammetry techniques has many applications in clinical, commercial, industrial, artistic, and entertainment areas. This work aims to create a methodology for improving 3D head reconstruction, with a focus on using selfie videos as the data source. Then, using this methodology, we seek to propose changes for the general-purpose 3D reconstruction algorithm to improve the head reconstruction process. We define the improvement of the 3D head reconstruction as an increase of reconstruction quality (which is lowering reconstruction errors of the head and amount of semantic noise) and reduction of computational load. We proposed algorithm improvements that increase reconstruction quality by removing image backgrounds and by selecting diverse and high-quality frames. Algorithm modifications were evaluated on videos of the mannequin head. Evaluation results show that baseline reconstruction is improved 12 times due to the reduction of semantic noise and reconstruction errors of the head. The reduction of computational demand was achieved by reducing the frame number needed to process, reducing the number of image matches required to perform, reducing an average number of feature points in images, and still being able to provide the highest precision of the head reconstruction.

Estimating a mathematical formula of soil erosion under the effect of rainfall simulation by digital close range photogrammetry technique

A new design of soil erosion and rainfall simulator is presented at this study as an attempt to deduce a mathematical formula of soil surface erosion phenomenon to describe the behavior of the sandy soil under the rainfall simulation, soil deformation such as the gullies and surface eroding rills are monitored by the Digital Close Range Photogrammetry (DCRP) technique that includes capturing digital images by a smart cellphone camera, and a Terrestrial Laser Scanner (TLS) to digitalize the soil surface as a point cloud data to produce Digital Elevation Models (DEM) with an accuracy reaches 0.10mm with the watershed, color relief, 3D surface model. The results show that the mentioned methods give a typical digital surface feature express especially of using geometrical adjustment that controls the orientation of the digital surface. The SIFT technology of the digital imaging feature detection achieves accurate results despite its small cost, 12% if compared to the TLS method. As a result of the statistical observations, a simple mathematical formula was generated through the DCRP technique that describes the sandy soil behavior under a hybrid technique of rainfall simulation as a relation between the eroding rate and the duration through the different gradient slopes.

Geotechnical slope stability and rockfall debris related safety assessments of rock cuts adjacent to a rail track using aerial photogrammetry data analysis

Transportation infrastructure facilitates the accessibility and mobility of goods, people, and services through its vast network spanning across the USA. The departments of transportation (DOT) agencies face many challenges in monitoring and maintaining these infrastructure assets for continuing their service and operations, especially those located adjacent to slopes in rural and remote areas. Mobilizing and conducting traditional infrastructure inspections in those conditions can be laborious and time-consuming. Also, the unstable or highly weathered rock slopes pose significant rockfall hazards due to the moisture content, intrusion, and temperature changes, transpired over a period of time, causing weathering and rockfalls, ultimately resulting in debris accumulation. Recently, unmanned aerial vehicles (UAVs) in conjunction with close-range photogrammetry techniques are being researched and used ubiquitously for infrastructure monitoring applications in and around mountainous regions. In this study, a rock-cut located in a remote terrain where a rail track was passing through was aerially inspected and imaged for performing a comprehensive safety assessment and analysis to evaluate the stability of rock-cut and ways to assess rockfall safety zones and boundaries. A unique approach was developed by leveraging the aerial mapping and data compilation along with an immersive three-dimensional visualization of slopes for conducting stability analysis followed by the evaluation of rockfall debris zones adjacent to rail tracks. Successful assessments conducted in this study indicate that the methodologies will benefit the transportation agencies in effectively monitoring and managing transportation infrastructure adjacent to hilly terrains and ensure the maintenance of safe clearance zones needed to safeguard the public and property.

IMPLEMENTATION OF CLOSE RANGE PHOTOGRAMMETRY USING MODERN NON-METRIC DIGITAL CAMERAS FOR ARCHITECTURAL DOCUMENTATION

The development of applied geodetic techniques for mapping and documentation of historical structures, buildings and sites is an important and vital purpose for contribution of any recording of cultural heritage for any country such as Egypt. This is done to preserve and restore any valuable architectural or other cultural monument, as a support to architectural, archaeological and other art-historical research throughout the ages. The purpose of this paper is to use close range photogrammetry technique (CRP) to reconstruct 3D model of architectural and historical mosque facade and comparing the accuracy of using digital commercial non-metric cameras with different resolutions and metric camera with flatbed scanner and photogrammetric scanner for architectural building documentation. El-Nasr Mosque façade in Mansoura city, Egypt was chosen as a case study in this paper. At first, twenty five points were selected at mosque façade at different elevations and distributed at different façade surfaces and observed using total station. Some of these points were selected as control points and the others were selected as check points to validate the results. Effect of control point’s number on image processing and analysis is also studied. Three cameras positions were selected for imaging to get the full details of mosque façade. Close range Digital Workstation (CDW) program was used for processing and analysis of multiple images. The results are indicated that close range photogrammetry using metric camera with photogrammetry scanner instead of flatbed scanner in technique is accurate enough to be beneficial in 3D architectural building documentation. Digital cameras with CRP technique give up different accuracy that depends mainly on the resolution of cameras and camera specifications.

A Novel Three-Dimensional Interactive Virtual Face to Facilitate Facial Anatomy Teaching Using Microsoft HoloLens.

In-depth understanding of facial anatomy is the foundation of clinical education and practices. Lately, anatomy education has undergone many changes due to the adoption of integrated medical curriculums. The time allocated to anatomy teaching on occasion been shortened to allow more time for clinical education. Innovation in visual technology such as virtual reality (VR), augmented reality (AR) and mixed reality (MR) has added a new dimension to anatomy education. The authors present a mixed reality virtual face model to facilitate complex anatomy teaching using Microsoft HoloLens in various educational settings. Close-range photogrammetry technique was utilised to construct a virtual face using a dissected fresh-frozen cephalus. Scanning was undertaken using DSLR cameras, capable of capturing ten frames per second, in ten different angles on the dissected side and four for the undissected side. The images of the entire cephalous were also separately captured in twenty different angles. These images were processed using software to reconstruct the three-dimensional virtual face. The virtual face using a mixed reality platform was able to demonstrate individual layers of the face and relevant clinically significant structures clearly with interactive labelling. Face and the content validity by 12 experts (plastic surgeons and dermatologists) demonstrated strong inter-rater reliability expressed as interclass correlation coefficient. An immersive experience by using Microsoft HoloLens provides an accurate 3D perception of the face to enhance anatomy learning. This can be utilised in undergraduate, postgraduate and continued medical education as an additional teaching tool in the constraints of cadaveric dissection. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Reliability of a close-range photogrammetry technique to measure ankle kinematics during active range of motion in place

BackgroundAs the risk of ankle turn during daily activity is very high, studying ankle kinematics in place is important for ankle sprain prevention. The close-range photogrammetry (CRP) technique is used to measure ankle kinematics during active range of motion (AROM) in place. The purpose of the study was to assess the reliability of CRP to measure ankle kinematics. MethodsTwenty adults were recruited and fourteen retro-reflective targets were mounted on the skin of their right feet. Imaging sensors were self-calibrated using a bundle adjustment technique, and the images were downloaded with Australis photogrammetric software. Three trials were conducted and reliability coefficients were used to assess agreement between them. ResultsReliability was almost perfect and the results show that the intraclass correlation coefficient (ICC) of ankle angle values were (dorsiflexion = 0.96), (plantarflexion = 0.81), (inversion = 0.92), (eversion = 0.95), (internal rotation = 0.92), and (external rotation = 0.78). The overall intraclass correlation coefficient was 0.89 and the standard error of the measurement (SEM) values ranged from (0.37° to 6.18°). ConclusionsThe results indicate that the CRP technique was able to reliably measure ankle kinematics. The results may support and enhance knowledge related to ankle AROM in the clinical arena.

DEM modeling of large-scale triaxial test of rock clasts considering realistic particle shapes and flexible membrane boundary

This paper presents a novel framework for the discrete modeling of the large-scale triaxial test of rock clasts, considering both the realistic particle shapes and veritable flexible boundary condition. First, real-shaped particle models for the tested rock clasts are precisely reconstructed using the close-range photogrammetry technique. The rubber membrane was modeled by a series of bonded particles. Then, the laboratory procedures of the triaxial test, i.e., sample preparation, isotropic compression, and shearing, are reproduced in the DEM simulations with consideration of the veritable confining boundary. To ensure more reliable numerical results, a systematic DEM calibration framework is established to determine the modeling parameters based on a series of calibration experiments, including tensile test, suspension test, clast-membrane sliding test, and large-scale triaxial test. Finally, the proposed method is applied to investigate the effects of confining pressure on the macro- and micro-mechanical behaviors of rock clasts. The presented works lay a foundation for further studies on revealing the mechanisms of the conventional triaxial test, e.g., the effect of end restraint and rubber membrane. Moreover, the proposed systematic framework for calibration of modeling parameters can be applied to precisely capture the real mechanical properties of various types of granular rock-like materials in DEM simulations.

Estimating a mathematical formula of soil erosion under the effect of rainfall simulation by digital close range photogrammetry technique

A new design of soil erosion and rainfall simulator is presented at this study as an attempt to deduce a mathematical formula of soil surface erosion phenomenon to describe the behavior of the sandy soil under the rainfall simulation, soil deformation such gullies and surface eroding rills are monitored by the Digital Close Range Photogrammetry (DCRP) technique that includes capturing digital images with a smart cellphone camera, and a Terrestrial Laser Scanner (TLS) to digitalize the soil surface as a smart point cloud data to produce Digital Elevation Models (DEM) with accuracy reaches 0.10 mm 3D surface model. The results show that the mentioned methods give typical digital surface feature express especially of using geometrical adjustment that controls the orientation of the digital surface, the digital imaging feature detection technology achieves accurate results despite its small cost compared to the laser scanner that the cost of imaging equipment and software are used did not exceed 12% of TLS cost. Results of the statistical observations, a 3 order polynomial mathematical formula was generated through the digital photogrammetry method that describes the sandy soil behavior under the rainfall simulation as a relation between the eroding rate and the duration through the different slopes.

Using Close-Range Photogrammetry to Measure Pavement Texture Characteristics and Predict Pavement Friction

Pavement friction measurements are collected and used to assess the functional characteristics of pavements to ensure an adequate level of friction. There are several factors that affect pavement friction including the properties of the tire rubber materials and pavement surface texture characteristics. This study utilized the close-range photogrammetry (CRP) technique to measure the pavement macrotexture and microtexture. Texture parameters were calculated from the collected and analyzed images of the pavement surface. The results of the CRP texture measurements were compared with typical measurement methods. The CRP texture measurements had excellent correlation with the measurement methods used in this study; however, the CRP offers a simple and accurate, yet inexpensive, alternative to the current methods used to measure surface macrotexture and microtexture. In addition, the CRP texture parameters were incorporated in the Persson friction model to predict skid friction as a function of rubber properties. The results demonstrated an excellent correlation between measured and predicted friction. This study greatly simplified the texture parameter calculations needed in the Persson friction model with good accuracy.

Assessment of the Three-Dimensional Model Produced by Photogrammetric and Geodetic Surveying Techniques

A combination of close-range photogrammetry techniques and geodetic surveying techniques are used to produce the three-dimensional model, which is one of the major tasks in the field of surveying at present because it is used in many engineering applications, industrial, medical and in cultural heritage objects which requires regular monitoring because of the high accuracy and reliability needed to conduct the measurements. The study area was in the university of Baghdad, specifically for the building of the university tower this research has been produced the three dimensional model of the tower depending on the overlapping ground images captured by a digital camera and the total station instrument used to measure the coordinates of ground points distributed on the university of Baghdad tower. The mathematical model used in this study is the direct linear transformation method to intensify ground points which are used to produce the three-dimensional model of the university tower. Also, a photogrammetric program is used to compute the object space coordinates from the point cloud three-dimensional modeling.

Digital Construction of Traditional Baruk in Sarawak, Malaysia

The traditional Baruk in Sarawak has gone through some architectural changes in terms of its material and function due to the urban modernization and safety concern. Therefore, the research aims to construct the Three-Dimensional (3D) model of the building using digital close-range photogrammetry. The exploratory study can be categorized into four phases consist of Site Selection; Data Acquisition; Data Processing; and 3D Modelling. The 3D model generated from the photogrammetry software presents the result of the dense point clouds. The study could give fundamental guidelines on using a mobile device in digital close-range photogrammetry techniques. Keywords: Digital construction; traditional architecture, digital close-range photogrammetry, heritage documentation. eISSN: 2398-4287© 2020. The Authors. Published for AMER ABRA cE-Bs by e-International Publishing House, Ltd., UK. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of AMER (Association of Malaysian Environment-Behaviour Researchers), ABRA (Association of Behavioural Researchers on Asians) and cE-Bs (Centre for Environment-Behaviour Studies), Faculty of Architecture, Planning & Surveying, Universiti Teknologi MARA, Malaysia. DOI: https://doi.org/10.21834/ebpj.v5i14.2243

Object-Based Analysis Using Unmanned Aerial Vehicles (UAVs) for Site-Specific Landslide Assessment

The increased development of computer vision technology combined with the increased availability of innovative platforms with ultra-high-resolution sensors, has generated new opportunities and fields for investigation in the engineering geology domain in general and landslide identification and characterization in particular. During the last decade, the so-called Unmanned Aerial Vehicles (UAVs) have been evaluated for diverse applications such as 3D terrain analysis, slope stability, mass movement hazard and risk management. Their advantages of detailed data acquisition at a low cost and effective performance identifies them as leading platforms for site-specific 3D modelling. In this study, the proposed methodology has been developed based on Object-Based Image Analysis (OBIA) and fusion of multivariate data resulted from UAV photogrammetry processing in order to take full advantage of the produced data. Two landslide case studies within the territory of Greece, with different geological and geomorphological characteristics, have been investigated in order to assess the developed landslide detection and characterization algorithm performance in distinct scenarios. The methodology outputs demonstrate the potential for an accurate characterization of individual landslide objects within this natural process based on ultra high-resolution data from close range photogrammetry and OBIA techniques for landslide conceptualization. This proposed study shows that UAV-based landslide modelling on the specific case sites provides a detailed characterization of local scale events in an automated sense with high adaptability on the specific case site.

Integration the Low Cost Camera Images with the Google Earth Dataset to Create a 3D Model

As known Close range photogrammetry represents one of the most techniques to create precise 3D model. Metric camera, digital camera, and Laser scanning can be exploited for the photogrammetry with variety level of cost that may be high. In this study, the cost level is taken in to consideration to achieve balance between the cost and the obtained accuracy. This study aims to detect potential of low cost tools for creating 3D model in terms of obtained accuracy and details and comparing it with corresponding studies. Smart phone camera is the most available for everyone; this gave the motivation for use in this study. In addition, Google Earth was used to integrate the 3D model produced from all sides including the roof. Then, two different types of the mobile camera were used in addition to the DSLR camera (Digital Single Lens Reflex) for comparison and analysis purposes. Thus, this research gave flexibility in work and low cost resulting from replacement the metric camera with the smart camera and the unmanned aerial vehicle (UAV) with Google Earth data. Mechanism of the work can be summarized in four steps. Firstly, photogrammetry planning to determine suitable baselines from object and location of targets that measured using GPS and Total station devices. Secondly, collect images using close range photogrammetry technique. Thirdly, processing step to create the 3D model and integrated with Google Earth images using the Agi Photoscan software. Finally, Comparative and evaluation stage to derive the accuracy and quality of the model obtained from this study using statistical analysis method. Regarding this Study, University of Baghdad, central library was selected as the case study. The results of this paper show that the low cost 3D model resulted from integrating phone and Google Earth images gave suitable result with mean accuracy level reached to about less than 5 meters compared with DSLR camera result, this may be used for several applications such as culture heritage and architecture documentation.

Assessment of disturbance impact of hydraulic jacked-in pile penetration in artificial clayey soil

The jacked-in pile method provides a substitute procedure that permits the installation of pre-formed piles with negligible vibration in a noiseless manner, thereby reducing noise impacts in marine and urban environments. This research was carried out by using a small-scale physical modelling approach to examine the movement of soil during pile installation. The model soil was formulated from a mix of amorphous silica and mineral oils; the resulting mixture was subjected to consolidation in a transparent chamber. The model pile was driven vertically down the mid-point of the soil model at different vertical speeds using a strain control device. The array of soil displacement dispersal was obtained by utilising the close-range photogrammetry and particle image velocimetry techniques. The deformation of soil during pile installation was found to decrease with progressive increase of the penetration rate. This result can be employed in the assessment of the disturbance effects of pile installation on underground services and archaeological relics beneath the ground in both urban and marine environments.

Research on the Design and Automatic Recognition Algorithm of Subsidence Marks for Close-Range Photogrammetry.

In China, traditional techniques for measuring structural subsidence cannot keep pace with the rapid development of critical national infrastructure such as the growing network of high-speed railways. Traditional monitoring methods using leveling instruments are inefficient and time consuming when monitoring structures like bridges and tunnels. Thus, a fast, economical, and more accurate and precise way to survey building subsidence is urgently needed to address this problem. This paper introduces a new close-range photogrammetry technique that deploys a fixed camera with tilt compensator to measure changes in height over small areas. A barcode subsidence mark that can be identified automatically during digital image processing replaces the leveling points used in traditional methods. Four experiments at different locations verified that results from the new method were stable and consistent with total station measurements. This approach is simple, inexpensive, and produces accurate and precise results as our evaluation results show.