Rapid imaging in the field followed by photogrammetry digitally captures the otherwise lost dimensions of plant specimens

Premise

We recognized the need for a customized imaging protocol for plant specimens at the time of collection for the purpose of three-dimensional (3D) modeling, as well as the lack of a broadly applicable photogrammetry protocol that encompasses the heterogeneity of plant specimen geometries and the challenges introduced by processes such as wilting.

Methods and Results

We developed an equipment list and set of detailed protocols describing how to capture images of plant specimens in the field prior to their deformation (e.g., with pressing) and how to produce a 3D model from the image sets in Agisoft Metashape Professional.

Conclusions

The equipment list and protocols represent a foundation on which additional improvements can be made for specimen geometries outside of the range of the six types considered, and an easy entry into photogrammetry for those who have not previously used it.

Measurement of Rock Joint Surfaces by Using Smartphone Structure from Motion (SfM) Photogrammetry

The measurement of rock joint surfaces is essential for the estimation of the shear strength of the rock discontinuities in rock engineering. Commonly used techniques for the acquisition of the morphology of the surfaces, such as profilometers and laser scanners, either have low accuracy or high cost. Therefore, a high-speed, low-cost, and high-accuracy method for obtaining the topography of the joint surfaces is necessary. In this paper, a smartphone structure from motion (SfM) photogrammetric solution for measuring rock joint surfaces is presented and evaluated. Image datasets of two rock joint specimens were taken under two different modes by using an iPhone 6s, a Pixel 2, and a T329t and subsequently processed through SfM-based software to obtain 3D models. The technique for measuring rock joint surfaces was evaluated using the root mean square error (RMSE) of the cloud-to-cloud distance and the mean error of the joint roughness coefficient (JRC). The results show that the RMSEs by using the iPhone 6s and Pixel 2 are both less than 0.08 mm. The mean errors of the JRC are -7.54 and -5.27% with point intervals of 0.25 and 1.0 mm, respectively. The smartphone SfM photogrammetric method has comparable accuracy to a 3D laser scanner approach for reconstructing laboratory-sized rock joint surfaces, and it has the potential to become a popular method for measuring rock joint surfaces.

Multi-Variant TLS and SfM Photogrammetric Measurements Affected by Different Factors for Determining the Surface Shape of a Thin-Walled Dome

The paper presents a combined analysis of terrestrial laser scanning (TLS) and structure from motion (SfM) photogrammetric measurement to determine an accurate model of the surface shape of a thin-walled dome. The analysis takes into account several factors that may affect the accuracy of measurement. In TLS measurements, these are related to scattering of the beam and its penetration into the structure of objects. Penetration of the beam into a synthetic structure changes the measured length. Shell moisture, caused by rainfall or dew effect, similarly affects the measured length, but the changes are dispersed. In the first case, it will change the size of the object, and in the second one, it generates measurement noise. SfM photogrammetric problems, such as object gloss and ambient reflection, lack of detail, and different results from software creating point clouds were also analyzed. An interesting observation was the significant influence of atmospheric pollution, sedimented on the lower half of the glossy dome, on increasing the accuracy of photogrammetric measurement. The analyses contain a number of cases that take into account the complex problems of obtaining and processing data of such facilities: periodic measurement, TLS and SfM photogrammetric measurement, measurement outside and inside the object, determination of the wall thickness, comparison with the project and free-sphere fitting, and use of dome rotation during TLS.

Feasibility Assessments Using Unmanned Aerial Vehicle Technology in Heritage Buildings: Rehabilitation-Restoration, Spatial Analysis and Tourism Potential Analysis

The Transylvanian region of Romania is a place of rich history since ancient times, where the original natural environment around architectural heritage sites or buildings has not been severely altered by urban development. Unfortunately, many such places are left by the authorities to degrade or totally collapse for lack of funds, vision or initiatives. The current paper addresses the potential of Unmanned Aerial Vehicles (UAVs) in the assessment of a viable and feasible prospect of restoration on a 19th century mansion that belonged to a nobiliary family. UAV use is rising in many industries and has become very popular in the last decade, but for survey engineering and related domains they represent a quantum leap in technology. Integrating UAV-acquired data and structure from motion software, has enabled modern techniques to obtain useful metrics from the field, accurate photorealistic 3D models for visual inspection, structural damage analyses, architectural rehabilitation-restoration, conservation and spatial analysis of the surrounding area. In this work a socio-cultural planning and design process is explored and presented to improve the local community and inclusion in a tourist circuit based on the regional potential, as well as an evaluation of accessibility derived from a vector-raster database that highlights the central position of the cultural heritage in regards to the axis of circulation between the important metropolitan areas and the local tourist attractions. This established workflow of modern topographic and construction measurements is fully integrable into the architectural process, building information modelling, heritage conservation and reconstruction.

Photogrammetry vs CT Scan: Evaluation of Accuracy of a Low-Cost Three-Dimensional Acquisition Method for Forensic Facial Approximation

Photogrammetry is a three-dimensional acquisition method potentially applicable to the forensic field. This possibility requires the verification of its accuracy. In this study, 3D volumes of skulls are generated to compare the photogrammetry versus the CT scan. In order to provide eligible material to the photogrammetric software, photographs were captured at a distance of 30 cm from the skull placed on a support 1 m in height and illuminated with diffused laboratory ceiling artificial light. A Nikon Coolpix P7100 camera was used. Photographs capture common elements with the previous and the next photograph so as to allow the photogrammetric software to recognize these common points between photographs and create a 3D puzzle. The Zephyr Lite (3DFlow©) software was employed to register the 3D volume. CT-based skulls are taken as a metric reference. The photogrammetry-based skulls are then enlarged according to the measurements of some landmarks or Zygion and Zygion, the distance between end of nasal and base of nasal pyramid for frontal projection, and minimum breadth of the mandibular ramus for the right lateral projection. The accuracy of the photogrammetry is compared to that of the CT scan by measuring the 3D volumes of the skulls studied. Specific landmarks are used as reference points for the measures in both frontal and lateral views. Bland-Altman graph shows homogeneity. The mean difference (1.28 mm) indicates that the measurements taken on the photogrammetry-based skull tend to slightly overestimate compared with the measurements taken on the CT-based skull.