Topographic surveys inevitably contain error, introducing uncertainty into estimates of volumetric or mean change based on the differencing of repeated surveys. In the geomorphic community, ...uncertainty has often been framed as a problem of separating out real change from apparent change due purely to error, and addressed by removing measured change considered indistinguishable from random noise from analyses (thresholding). Thresholding is important when quantifying gross changes (i.e. total erosion or total deposition), which are systematically biased by random errors in stable parts of a landscape. However, net change estimates are not substantially influenced by those same random errors, and the use of thresholds results in inherently biased, and potentially misleading, estimates of net change and uncertainty. More generally, thresholding is unrelated to the important process of propagating uncertainty in order to place uncertainty bounds around final estimates. Error propagation methods for uncorrelated, correlated, and systematic errors are presented. Those equations demonstrate that uncertainties in modern net change analyses, as well as in gross change analyses using reasonable thresholds, are likely to be dominated by low‐magnitude but highly correlated or systematic errors, even after careful attempts to reduce those errors. In contrast, random errors with little to no correlation largely cancel to negligible levels when averaged or summed. Propagated uncertainty is then typically insensitive to the precision of individual measurements, and is instead defined by the relative mean error (accuracy) over the area of interest. Given that real‐world mean elevation changes in many landscape settings are often similar in magnitude to potential mean errors in repeat topographic analyses, reducing highly correlated or systematic errors will be central to obtaining accurate change estimates, while placing uncertainty bounds around those results provides essential context for their interpretation. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.
The analysis of landscape change based on repeat topographic surveys is becoming an increasingly practical and powerful tool across many earth surface disciplines. This paper re‐iterates the importance of accounting for survey error through error propagation, including subtle systematic errors, and presents statistical methods for doing so. The common practice of removing change measurements below some limit of detection (“thresholding”) is shown to provide biased and potentially misleading results when used to assess net volumetric or mean change.
The paper presents the results of the study of the photogrammetric models quality depending on the photogrammetric survey. The presented data have been obtained by the Xiaomi Mi Home Security Camera ...360. We examined the texture of the captured object and the general geometric parameters of the created photographing basis as the experimental variable. As a result, the paper contains general recommendations for the cameras optimal location for photogrammetric surveying in low light and space limits. The main author's idea of the improvement of the photogrammetric models quality is projecting a temporary artificial texture on the subject of surveying.
Retaining walls are often needed near railway tracks, to maintain the geometry of the surrounding earth and thus ensure the safety of the trains. Their maintenance can pose a challenge due to the ...shifting of the land over time which may cause landslides, that would potentially obstruct the railway and require manual intervention. As part of the Ferrovia 4.0 project which aims to improve Portuguese railways, a system was developed to capture the 3D shape of railway retaining walls as the train passes by.
The system makes use of two cameras, positioned at different angles to more easily obtain details of the retaining wall. An algorithm was developed, allowing the system to capture several images as the train passes through an area of interest, which are then processed using Pix4Dmapper, resulting in a point cloud of the retaining wall. The system starts and ends its acquisition automatically, depending on its GPS coordinates.
It was possible to successfully captures images of areas of interest and the resulting point clouds can be further analyzed to identify areas that may require intervention.
This work was developed in the scope of the project FERROVIA 4.0, n° 46111 which has received funding from “ANI - Agência Nacional de Inovação, S.A” through the programme “Mobilizador COPROMOÇÃO_PT2020”.
Structure-from-motion (SfM) photogrammetry has become ubiquitous in the geosciences, owing to its low-cost and ease of use for generating 3D data. Ideas around data collection, quality and processing ...need to be revisited to ensure that the technology is being harnessed correctly. One area which is new in this current image acquisition boom is the range of sensors and systems being used to collect image data. This raises crucial questions in the geoscience community which are addressed in this contribution. This is split into three parts. Firstly, image quality is investigated to establish whether a stable association between it and the quality of photogrammetric products can be uncovered to allow simpler and more effective inter-comparison of results between studies. This was accomplished by artificially degrading a very high-quality benchmark dataset of a coastal cliff and a landslide in Norfolk, UK. Results revealed that the level of noise, image compression and downsampling all degrade the quality of 3D products from the SfM workflow. Secondly, these sets of images were pre-processed to establish whether results could be augmented by controlling the single colour channel used during photogrammetric processing. Results showed slight variations in the products generated, with evidence supporting the fine sensitivity SfM has for refining the focal length estimation of the lens. For extremely specific contexts, pre-processing of the RGB-to-single channel conversion may be relevant, but for the datasets analysed in this contribution this was not the case. Thirdly, image network configurations were investigated to build on previous research in establishing best practice. Results show that, in situations where the number of images being acquired is a limiting factor, networks with narrowly oblique overlapping images have a higher density and lower error than those with widely oblique images and those directly facing the surface normal. These results demonstrate the value of optimising image acquisition, and in the handling of this imagery. The differences in image quality and pre-processing which are unreported within geoscientific studies using SfM could account for differences between accuracies obtained, independent of the specific photogrammetric methods used. Insights from this work into how best to capture, process and produce the best quality SfM data will allow the community to adopt these best practices in the future.
Studying flowers in 3D using photogrammetry Leménager, Marion; Burkiewicz, Jérôme; Schoen, Daniel J. ...
The New phytologist,
March 2023, 2023-03-00, 20230301, Letnik:
237, Številka:
5
Journal Article
Recenzirano
Summary
Flowers are intricate and integrated three‐dimensional (3D) structures predominantly studied in 2D due to the difficulty in quantitatively characterising their morphology in 3D. Given the ...recent development of analytical methods for high‐dimensional data, the reconstruction of flower models in three dimensions represents the limiting factor to studying flowers in 3D.
We developed a floral photogrammetry protocol to reconstruct 3D models of flowers based on images taken with a digital single‐lens reflex camera, a turntable and a portable lightbox.
We demonstrate that photogrammetry allows a rapid and accurate reconstruction of 3D models of flowers from 2D images. It can reconstruct all visible parts of flowers and has the advantage of keeping colour information. We illustrated its use by studying the shape and colour of 18 Gesneriaceae species.
Photogrammetry is an affordable alternative to micro‐computed tomography (micro‐CT) that requires minimal investment and equipment, allowing it to be used directly in the field. It has the potential to stimulate research on the evolution and ecology of flowers by providing a simple way to access 3D morphological data from a variety of flower types.
Channel incision is an evident trend for river evolution in many European rivers and notably the Western Carpathians, whose former braided and multichannel wandering river system is transforming into ...a single‐thread channel, but it is often difficult to separate drivers and determine if incision is finished or is still ongoing. To overpass these research gaps, this paper presents an innovative approach to assess the multidecadal incision of the Belá River in the Western Carpathians since 1949 by LiDAR‐based analyses of floodplain surfaces above the river channel dated from historical aerial images. Detailed analyses of ongoing incision were also calculated based on DEM of differences (DoD) using Structure‐from‐Motion (SfM) photogrammetry‐derived topo‐bathymetric models. The study applied the BACI (Before‐After‐Control‐Impact) approach that compared pre‐state (Before), post‐state (After) and reach (Control) that is not affected by potential external effects with degraded (impacted) reach to be able to distinguish the driver effects. Floodplain channel surface analyses indicate the maximum incision up to 4 m and incision rate of 5.7 cm/year that occurred in the most degraded reach. Moreover, cross‐section profiles point to accelerated incision of 24.5 cm/year in the last 10 years (2011–2021) by the propagation of incision upstream. Overall, the net changes from the UAV survey pointed to 22 759 m3 of gravel sediments, constituting outwash from the 1.6 km long channel system (2015–2022) by incision, whereas analyses of historical channel surfaces estimated erosion of 573 303 m3 from impacted reaches between 1949 and 2020. Incision evidence is only observed in the downstream part below the control section due to local drivers (channel regulation, comprising embankment and gravel mining that activated a backward erosion of the system with knickpoint migration upstream). This analysis shows the benefits of combining different sources of data to separate long‐term and ongoing channel responses and the BACI‐approach to better target cause–effect relationships in space and time.
The paper presents an innovative approach to assess the multidecadal incision since 1949 by LiDAR‐based analyses of floodplain surfaces above the river channel dated from historical aerial images. Detailed analyses of ongoing incision were also calculated based on DEM of differences (DoD) using structure‐from‐motion (SfM) photogrammetry‐derived topo‐bathymetric models.
Several factors contribute to the anatomical complexity of the trochlear nerve, including small diameter, complex and longest intracranial course, deep location, and numerous neurovascular ...relationships. A 3-dimensional (3D) photorealistic model of the cranial nerves provides a detailed and immersive representation of the anatomy, enabling one to improve surgical planning, advanced surgical research, and training. The purpose of this work is to present a 3D photogrammetric study for a more intuitive and interactive way to explore and describe the entire course of trochlear nerve.
Two injected-fixed head human specimens (4 sides) were examined. The dissection protocol was divided into the following steps: 1) brain hemisphere exposure; 2) hemispherectomy dissecting all cranial nerves and partial removal of the free edge of the tentorium; 3) middle fossa and lateral wall of cavernous sinus exposure; and 4) orbital exposure. A detailed 3D photogrammetric model was generated for each dissection step.
Four main volumetric models were generated during a step-by-step layered dissection of the entire nerve pathway highlighting its different segments. Finally, a full and integrated model of the entire course of the nerve was created. The models are available for visualization on monoscopic display, virtual, and augmented reality environment.
The present photogrammetric model provides a more comprehensive understanding of the nerve’s anatomy in its different segments, allows for customizable views thus simulating different perspectives, and can be a valuable alternative to traditional dissections. It is an advanced tool for surgical planning and surgical simulation as well as virtual reality representation of the anatomy.
The availability of high‐resolution, multi‐temporal, remotely sensed topographic data is revolutionizing geomorphic analysis. Three‐dimensional topographic point measurements acquired from ...structure‐from‐motion (SfM) photogrammetry have been shown to be highly accurate and cost‐effective compared to laser‐based alternatives in some environments. Use of consumer‐grade digital cameras to generate terrain models and derivatives is becoming prevalent within the geomorphic community despite the details of these instruments being largely overlooked in current SfM literature.
A practical discussion of camera system selection, configuration, and image acquisition is presented. The hypothesis that optimizing source imagery can increase digital terrain model (DTM) accuracy is tested by evaluating accuracies of four SfM datasets conducted over multiple years of a gravel bed river floodplain using independent ground check points with the purpose of comparing morphological sediment budgets computed from SfM‐ and LiDAR‐derived DTMs. Case study results are compared to existing SfM validation studies in an attempt to deconstruct the principle components of an SfM error budget.
Greater information capacity of source imagery was found to increase pixel matching quality, which produced eight times greater point density and six times greater accuracy. When propagated through volumetric change analysis, individual DTM accuracy (6–37 cm) was sufficient to detect moderate geomorphic change (order 100 000 m3) on an unvegetated fluvial surface; change detection determined from repeat LiDAR and SfM surveys differed by about 10%. Simple camera selection criteria increased accuracy by 64%; configuration settings or image post‐processing techniques increased point density by 5–25% and decreased processing time by 10–30%.
Regression analysis of 67 reviewed datasets revealed that the best explanatory variable to predict accuracy of SfM data is photographic scale. Despite the prevalent use of object distance ratios to describe scale, nominal ground sample distance is shown to be a superior metric, explaining 68% of the variability in mean absolute vertical error. Published 2016. This article is a U.S. Government work and is in the public domain in the USA
Background: Photogrammetric analysis of facial soft tissue plays an important role in facial plastic surgeries. In many countries, planning for facial plastic surgery is done based on the defined ...facial metric standards for the same society. Few research works have been conducted in the field of facial cephalometric criteria of the Iranian race. The main goal of this study is to determine the average values of facial profile view metrics of people referred to Imam Reza Hospital (Ardabil). Methods: First, in a period of 3 months, facial profile view images of the referred patients including 30 males and 30 females were provided. Then, the angular criteria of the profile view were measured by selecting 11 facial anatomical landmarks applicable for Rhinoplasty and Mentoplasty surgeries in the MATLAB software. Results: The results showed that among the facial profile view metrics, the Nasofrontal, Nose Tip and Mentolabial angles are close to the criteria of the Turkish, Nepalese and Brazilian races, respectively. The Facial Convexity Including Nose (FCIN) metric is close to the Brazilian and Nepalese races, and also, Facial Convexity Excluding Nose (FCEN) is close to the Bangladesh and Brazilian races. Conclusion: In this study, cephalometric analysis of facial soft tissue was done by measuring the facial profile view metrics to help facial plastic surgeons. Considering the difference in facial metrics of Iranians with other races, the criteria measured in this study can be interesting for surgeons in planning of facial cosmetic surgeries, especially Rhinoplasty and Mentoplasty.
We propose a novel technique to measure the small-scale three-dimensional features of a shallow-water coral reef using a small drone equipped with a consumer-grade camera, a handheld GPS and ...structure from motion (SfM) algorithms. We used a GoPro HERO4 with a modified lens mounted on a DJI Phantom 2 drone (maximum total take-off weight <2 kg) to perform a 10 min flight and collect 306 aerial images with an overlap equal or greater than 90%. We mapped an area of 8380 m
2
, obtaining as output an ortho-rectified aerial photomosaic and a bathymetric digital elevation model (DEM) with a resolution of 0.78 and 1.56 cm pixel
−1
, respectively. Through comparison with airborne LiDAR data for the same area, we verified that the location of the ortho-rectified aerial photomosaic is accurate within ~1.4 m. The bathymetric difference between our DEM and the LiDAR dataset is −0.016 ± 0.45 m (1σ). Our results show that it is possible, in conditions of calm waters, low winds and minimal sun glint, to deploy consumer-grade drones as a relatively low-cost and rapid survey technique to produce multispectral and bathymetric data on shallow-water coral reefs. We discuss the utility of such data to monitor temporal changes in topographic complexity of reefs and associated biological processes.
PDF
