Laser Photogrammetry Research Articles

A functional regression model for inventories supported by aerial laser scanner data or photogrammetric point clouds

Abstract Forest inventories, with a probability sampling of a target variable Y and a potentially very large number of auxiliary variables (X) obtained from an aerial laser scanner or photogrammetry, are faced with the issue of model and variable selection when a model for linking Y to X is formulated. To bypass this step we propose a generic functional regression model (FRM) for use in both a design- and a model-based framework of inference. We demonstrate applications of FRM with inventory data from France, Germany, and Norway. The generic FRM achieved results that were comparable to those obtained with more traditional approaches based on model and variable selections. The proposed FRM generates interpretable regression coefficients and enables testing of practically relevant hypotheses regarding estimated models.

Automatic registration of MLS point clouds and SfM meshes of urban area

Recent advances in 3D scanning technologies allow us to acquire accurate and dense 3D scan data of large-scale environments efficiently. Currently, there are various methods for acquiring large-scale 3D scan data, such as Mobile Laser Scanning (MLS), Airborne Laser Scanning, Terrestrial Laser Scanning, photogrammetry and Structure from Motion (SfM). Especially, MLS is useful to acquire dense point clouds of road and road-side objects, and SfM is a powerful technique to reconstruct meshes with textures from a set of digital images. In this research, a registration method of point clouds from vehicle-based MLS (MLS point cloud), and textured meshes from the SfM of aerial photographs (SfM mesh), is proposed for creating high-quality surface models of urban areas by combining them. In general, SfM mesh has non-scale information; therefore, scale, position, and orientation of the SfM mesh are adjusted in the registration process. In our method, first, 2D feature points are extracted from both SfM mesh and MLS point cloud. This process consists of ground- and building-plane extraction by region growing, random sample consensus and least square method, vertical edge extraction by detecting intersections between the planes, and feature point extraction by intersection tests between the ground plane and the edges. Then, the corresponding feature points between the MLS point cloud and the SfM mesh are searched efficiently, using similarity invariant features and hashing. Next, the coordinate transformation is applied to the SfM mesh so that the ground planes and corresponding feature points are adjusted. Finally, scaling Iterative Closest Point algorithm is applied for accurate registration. Experimental results for three data-sets show that our method is effective for the registration of SfM mesh and MLS point cloud of urban areas including buildings.

Using minimally invasive techniques to determine green sea turtle Chelonia mydas life-history parameters

Determining the life history and population parameters of sea turtles typically involves the live capture of animals. Photo-identification (photo-ID) of free-ranging individuals is a cost-effective alternative to conventional tagging for mark-recapture studies that also minimises the risk of injury or stress to the animals. Paired laser-photogrammetry (photogrammetry) is a minimally invasive technique to size animals and has been proven effective in a range of different taxa. Photo-ID and photogrammetry were combined as minimally invasive techniques to determine life-history parameters of free-ranging green sea turtles Chelonia mydas at a site in Oslob, Cebu, Philippines. The pattern-recognition software I3S Pattern was used to validate results and confirm visual matching. A total of 38 individuals were identified at the site through photo-ID. Facial scutes remained unchanged for a min. of 3.6years. Photogrammetry was employed to measure straight carapace lengths (SCLs) of a sample of 17 individuals, with a mean straight carapace length of 52.5±SD 1.1cm. Modified maximum likelihood methods were used to model mean residency of 873d at the site, with c. 12 individuals present at any one time. Based on photogrammetry measurements, individuals at the site were found to be of immature age class. This, along with the extended residency times, indicates that the site could be an important developmental habitat. Photo-ID is a valid minimally invasive technique for identifying individual C. mydas for mark-recapture analyses. The use of paired laser photogrammetry for categorising the life-history stage of an aggregation of sea turtles is demonstrated for the first time. Identification of such developmental habitats through the employment of these minimally invasive techniques is useful for conservation of the species.

DIRECT IMAGE-TO-GEOMETRY REGISTRATION USING MOBILE SENSOR DATA

Adding supplementary texture and 2D image-based annotations to 3D surface models is a useful next step for domain specialists to make use of photorealistic products of laser scanning and photogrammetry. This requires a registration between the new camera imagery and the model geometry to be solved, which can be a time-consuming task without appropriate automation. The increasing availability of photorealistic models, coupled with the proliferation of mobile devices, gives users the possibility to complement their models in real time. Modern mobile devices deliver digital photographs of increasing quality, as well as on-board sensor data, which can be used as input for practical and automatic camera registration procedures. Their familiar user interface also improves manual registration procedures. This paper introduces a fully automatic pose estimation method using the on-board sensor data for initial exterior orientation, and feature matching between an acquired photograph and a synthesised rendering of the orientated 3D scene as input for fine alignment. The paper also introduces a user-friendly manual camera registration- and pose estimation interface for mobile devices, based on existing surface geometry and numerical optimisation methods. The article further assesses the automatic algorithm’s accuracy compared to traditional methods, and the impact of computational- and environmental parameters. Experiments using urban and geological case studies show a significant sensitivity of the automatic procedure to the quality of the initial mobile sensor values. Changing natural lighting conditions remain a challenge for automatic pose estimation techniques, although progress is presented here. Finally, the automatically-registered mobile images are used as the basis for adding user annotations to the input textured model.

Mining Shaft Inspection by Laser Photogrammetry

One of the most important tasks in the area of mining safety is the inspection of vertical mining shaft. Geological processes in the rock mass rise problems with all used mining components over a long-term period. There is a possibility of occurrence of an equipment deformation or destruction in all directions (there are installed pipelines, cables, long vertical linear guidance, etc. inside a shaft). Periodical inspection of mining shaft profile and its analysis are necessary to ensure a safe transport both of the material and especially staff. Base of the solution of this problem lies in the use of contactless measurement methods of the profile, such as photogrammetry described in this article. First it gives a description of photogrammetry problem, pros and cons of proposed implementation with solid state LED or LASER LED used as light sources (instead of xenon flash tube) as well as flash timing and control and spectral distribution of the light. Then computer analysis of mining shaft profile as a part of rapid diagnostics is described.DOI: http://dx.doi.org/10.5755/j01.eee.22.1.14109

Level Set Method for Surface Reconstruction and Its Application in Surveying

AbstractA novel approach to a three-dimensional (3D) model creation from data sets obtained by laser scanning or photogrammetry is presented, including a description of the method and efficient numerical algorithms for 3D model creation for surveying applications. The presented method solves the fundamental problem of surface reconstruction by constructing models using differential geometry and partial differential equations. The time-relaxed eikonal equation was used to obtain the distance function from the cloud of points, and the 3D model was then created by the evolution of an initial guess by the advection equation regularized by curvature, where the advective velocity is given by the gradient of the computed distance function. The partial differential equations were discretized by the finite-difference schemes, and the results of the 3D model creation are presented and discussed.

A minimally invasive technique to assess several life-history characteristics of the endangered great hammerhead shark Sphyrna mokarran.

A dorsal-fin photo-identification technique paired with a non-invasive parallel laser photogrammetry technique was used to non-invasively identify individual Sphyrna mokarran over time. Based on the data collected over a duration of 59 days, 16 different S. mokarran (mean ± S.D. pre-caudal length: 220·82 ± 13·66 cm; mean ± S.D. cephalofoil width: 71·38 ± 7·94 cm) were identified using dorsal-fin photo-identification, with a mean ± S.D. shark re-sighting frequency of 4·05 ± 3·06 at-sea days. The results illustrate a high S. mokarran sighting rate and therefore, the utilization of parallel laser photogrammetry and dorsal-fin photo-identification may be a plausible multi-year approach to aid in non-invasively determining the growth rate and inter-annual site fidelity of these animals.

Risks and advantages of using surface laser photogrammetry on free‐ranging marine organisms: a case study on white sharks Carcharodon carcharias

This study employed a non-lethal measurement tool, which combined an existing photo-identification technique with a surface, parallel laser photogrammetry technique, to accurately estimate the size of free-ranging white sharks Carcharodon carcharias. Findings confirmed the hypothesis that surface laser photogrammetry is more accurate than crew-based estimations that utilized a shark cage of known size as a reference tool. Furthermore, field implementation also revealed that the photographer's angle of reference and the shark's body curvature could greatly influence technique accuracy, exposing two limitations. The findings showed minor inconsistencies with previous studies that examined pre-caudal to total length ratios of dead specimens. This study suggests that surface laser photogrammetry can successfully increase length estimation accuracy and illustrates the potential utility of this technique for growth and stock assessments on free-ranging marine organisms, which will lead to an improvement of the adaptive management of the species.

Laser photogrammetry improves size and demographic estimates for whale sharks.

Whale sharks Rhincodon typus are globally threatened, but a lack of biological and demographic information hampers an accurate assessment of their vulnerability to further decline or capacity to recover. We used laser photogrammetry at two aggregation sites to obtain more accurate size estimates of free-swimming whale sharks compared to visual estimates, allowing improved estimates of biological parameters. Individual whale sharks ranged from 432–917 cm total length (TL) (mean ± SD = 673 ± 118.8 cm, N = 122) in southern Mozambique and from 420–990 cm TL (mean ± SD = 641 ± 133 cm, N = 46) in Tanzania. By combining measurements of stranded individuals with photogrammetry measurements of free-swimming sharks, we calculated length at 50% maturity for males in Mozambique at 916 cm TL. Repeat measurements of individual whale sharks measured over periods from 347–1,068 days yielded implausible growth rates, suggesting that the growth increment over this period was not large enough to be detected using laser photogrammetry, and that the method is best applied to estimating growth rates over longer (decadal) time periods. The sex ratio of both populations was biased towards males (74% in Mozambique, 89% in Tanzania), the majority of which were immature (98% in Mozambique, 94% in Tanzania). The population structure for these two aggregations was similar to most other documented whale shark aggregations around the world. Information on small (<400 cm) whale sharks, mature individuals, and females in this region is lacking, but necessary to inform conservation initiatives for this globally threatened species.

Modélisation géostructurale 3D de parois rocheuses par lasergrammétrie et photogrammétrie terrestres en milieu ferroviaire

Rock instabilities located along the national railway network are a real risk for safety and regularity of rail traffic. The project presented in this paper aims to optimize the methodology for geostructural characterization, resulting in an improved knowledge of the rock mass and better management of associated hazards affecting the railway system. As a consequence, a new approach is proposed in order to study the outcrops with the joint use of dense three-dimensional data and 2D digital images obtained by terrestrial laser scanning and photogrammetry. Using semi-automatic and/or assisted manual processing, the analysis of point clouds and photographs ultimately allows access to the main quantitative parameters characterizing the structure of the modeled rock walls. This set of developments has been integrated into a functional modeling tool: GAIA-GeoRoc. On the one hand, it makes massive amounts of dimensional data available to geologists; on the other hand, in a railway context, it improves our knowledge of the rock masses without risking the safety of personnel (thanks to non-contact measurements) or reducing the railway line capacity.

Population structure and residency patterns of whale sharks, Rhincodon typus, at a provisioning site in Cebu, Philippines.

This study represents the first description of whale sharks, Rhincodon typus, occurring at a provisioning site in Oslob, Cebu, Philippines. Frequent observations of sharks are often difficult, even at tourism sites, giving rise to provisioning activities to attract them. The present study provides repeated longitudinal data at a site where daily provisioning activities took place, and whale sharks were present every day. A total of 158 individual whale sharks were photographically identified between Mar 2012 and Dec 2013, with 129 males (82%), 19 females (12%) and 10 (6%) of undetermined sex. Mean estimated total length was 5.5 m (±1.3 m S.D.). Twenty individuals were measured with laser photogrammetry to validate researchers’ estimated sizes, yielding a good correlation (r2 = 0.83). Fifty-four (34%) individuals were observed being hand-fed by local fishermen (provisioned), through in-water behavioural observations. Maximum likelihood methods were used to model mean residency time of 44.9 days (±20.6 days S.E.) for provisioned R. typus contrasting with 22.4 days (±8.9 days S.E.) for non-provisioned individuals. Propeller scars were observed in 47% of the animals. A mean of 12.7 (±4.3 S.D.) R. typus were present in the survey area daily, with a maximum of 26 individuals (Aug 10 2013) and a minimum of 2 (Dec 6 2012). Twelve (8%) individuals were seen on at least 50% of survey days (n = 621), with a maximum residency of 572 days for one individual (P-396). Twenty four individuals were photographically identified across regional hotsposts, highlighting the species’ migratory nature and distribution. Extended residency and differences in lagged identification rates suggest behavioural modification on provisioned individuals, underlying the necessity for proper management of this tourism activity.

DIGITIZING METHODS IN REGENERATION OF MASONRY CASTLES / SKAITMENINIMO METODAI MŪRINIŲ PILIŲ REGENERACIJOJE

In monitoring, preservation and regeneration of masonry architectural heritage modern digital technologies increase performance speed and quality. In rehabilitation of masonry castles an important role is played by the digital technologies, such as laser scanning, photogrammetry, photography, two-dimensional design (2D) and three-dimensional design (3D). Fairly accurate view of the future and perceived space, restored interior and exterior details is created with the help of some or all of these technologies. Formation of the restored castle’s vision is also influenced by its urban environment, preserved authentic material and even modern heritage conservation theory. This article provides an overview of digitization techniques and their variations based on approved foreign materials and practices used in the process of masonry castles regeneration. Santrauka Siekiant išsaugoti, stebint ir regeneruojant mūrinės architektūros paveldą šiuolaikinių skaitmeninių technologijų naudojimas padidina veiklos spartą ir kokybę. Atgaivinant mūrines pilis svarbų vaidmenį atlieka skaitmeninės technologijos: lazerinis skenavimas, fotogrametrija, fotografija, dvimatis projektavimas (2D), trimatis projektavimas (3D). Pasitelkus keletą ar visas šias technologijas gana tiksliai sukuriamas būsimas vaizdas ir suvokiama erdvė, atkuriamos interjerų bei eksterjerų detalės. Atkuriamai pilies vizijai suformuoti turi įtakos urbanistinė aplinka, išlikusi autentiška medžiaga, šiuolaikinė paveldosaugos teorija. Šiame straipsnyje apžvelgiami mūro pilių regeneracijos procese naudotini skaitmeninimo metodai bei jų variacijos remiantis užsienyje aprobuota medžiaga ir praktika.

Digitizing Methods in Regeneration of Masonry Castles

In monitoring, preservation and regeneration of masonry architectural heritage modern digital technologies increase performance speed and quality. In rehabilitation of masonry castles an important role is played by the digital technologies, such as laser scanning, photogrammetry, photography, two-dimensional design (2D) and three-dimensional design (3D). Fairly accurate view of the future and perceived space, restored interior and exterior details is created with the help of some or all of these technologies. Formation of the restored castle’s vision is also influenced by its urban environment, preserved authentic material and even modern heritage conservation theory. This article provides an overview of digitization techniques and their variations based on approved foreign materials and practices used in the process of masonry castles regeneration.

The development of robust morphometric indices from accurate and precise measurements of free-swimming whale sharks using laser photogrammetry

To enable the study of population dynamics of wild animals the determination of the age, growth rate and maturity status of a sample of the individuals present is required; consequently, obtaining repeated accurate and precise total length (TL) measurements for individuals over time can be especially valuable. However, there are limited easily applied methods to ascertain the TL of large free-swimming fish, especially the largest extant species of fish, the whale shark (Rhincodon typus). This study expands on previous work and presents the results of a robust laser photogrammetry system developed to achieve accurate TL, pre-caudal length (PCL) and further morphometric measurements of whale sharks observed between 2009 and 2011 in seasonal feeding aggregations located in the Seychelles and Djibouti. Calculations for repeatability (r) indicated a high level of precision for the system with r approaching 1 for both TL and PCL, increasing further with the use of morphometric measurements. TL measurements of ‘straight sample sharks’ also provided geometric mean linear regression equations to enable the prediction of TL from defined morphological indices. Continuous validation of the system against objects of a fixed length also indicated a high level of accuracy for the method of measurement. We concluded that the laser photogrammetry system can be confidently employed to obtain accurate in-water TL, PCL and morphometric measurements for R. typus, with wide ranging implications and applications for the study of R. typus, and other large marine fauna.

How large is the world's largest fish? Measuring whale sharks Rhincodon typus with laser photogrammetry

Laser photogrammetry was found to be a promising new cost-effective technique for measuring free-swimming whale sharks Rhincodon typus. Photogrammetric measurements were more precise than visual size estimates by experienced researchers, with results from the two methods differing by 9· 8 ± 1· 1% (mean ±s.e.). A new metric of total length and the length between the fifth gill and first dorsal fin (r² = 0· 93) is proposed to facilitate easy, accurate length measurements of whale sharks in the field.

Assessment of epidermal condition and calf size of Fiordland bottlenose dolphin Tursiops truncatus populations using dorsal fin photographs and photogrammetry

The bottlenose dolphin Tursiops truncatus population in Doubtful Sound, New Zealand, has declined by over 34% since 1995 and is subject to potential impacts from tourism and habitat modification via freshwater discharge from a hydroelectric power station. The bottlenose dolphin population in neighbouring Dusky Sound is exposed to much lower levels of tourism and the fiord receives only natural freshwater runoff. We used dorsal fin identification photographs from both pop- ulations to compare levels of epidermal disease and laser photogrammetry to measure the dorsal fin base length of calves ( 95% of individuals), but lesion extent was 4 times higher in Doubtful Sound. Lesion extent was higher for female dolphins than for males in Doubtful Sound, but not in Dusky Sound. In Dusky Sound calves were larger at first observation and were born over a longer period. The short calving season in Doubtful Sound may be an adaptation to localized temperature conditions. Anthropogenic impacts may contribute to the higher levels of epidermal disease in the Doubtful Sound population. The higher extent of epidermal lesions in females and the smaller size of calves in Doubtful Sound may be a factor in the low survival of calves in the population.

New challenges for reverse engineering in facial treatments: How can the new 3D non-invasive surface measures support diagnoses and cures?

Reverse engineering can give new challenges for diagnosis and facial treatments, offering 3D measurements, impossible to obtain only few years ago, in terms of richness of information, precision, accuracy and reliability. In this paper the main aspects and methods for skull and facial scanning and measurement are analyzed, considering volumetric methods (CT, MRI) and surface approaches (laser scanning, structured light and photogrammetry). These latter are particularly interesting because they avoid exposing the patient to ionising radiation and to any biological risk. The EU directives in fact require minimisation of radiographic exposure, that will be in the near future justified only for real diseases, but not for aesthetic treatments and surgery, orthodontics, and malocclusions. Photogrammetry is very promising for the digital reconstruction of human faces; it seems to offer the best compromise with respect to realistic and accurate reproduction, processing time, simplicity and cost of equipment. New software platforms have been developed to integrate the information acquired using different tools: photogrammetry, CT/Cone beam computerized tomography (CBCT), laser scans of dental cast study models. In this way a powerful multi-user database system can be realised to track the patient's imaging history throughout the treatment cycle and to forecast the growth and the results of the treatments.

Laser photogrammetry to determine dorsal fin size in a population of bottlenose dolphins from Doubtful Sound, New Zealand

Laser photogrammetry (also known as laser-metrics) can provide valuable morphological data but the measurement error associated with the technique has not been quantified. Here laser-metrics were used to measure the dorsal fins of an entire resident population of bottlenose dolphins (Tursiops truncatus) from Doubtful Sound, New Zealand. Dorsal fin base length, height and surface area were measured from dorsal fin photographs. Sources of measurement error were estimated by repeatedly measuring multiple photographs of dorsal fins of known individuals. Measurement error accounted for less than 6% of the total variation in dorsal fin base length and height, indicating that the technique was repeatable. Adults were the only age-class to express sexual dimorphism, with males significantly larger than females in all measurements. The relationship between dorsal fin height and base length was significantly different between male and female adults: dorsal fins of males were proportionately taller. Laser photogrammetry is an inexpensive and non-invasive measurement technique that can provide valuable size data when used in conjunction with routine dorsal fin photo-identification studies.