Digital Single-lens Reflex Camera Research Articles

Effect of cross-polarization filters on the trueness of colors obtained with a single-lens reflex camera, macro lens, and a ring flash.

To investigate the effect of cross-polarization filters on the colors of shade tabs obtained with a digital single-lens reflex (DSLR) camera, macrolens, and a ring flash. Digital images of four shade tables (1M1, 3L2.5, 3R2.5, and 5M3) from the VITA Toothguide 3D-Master shade guide were taken using a DSLR camera, 100 mm macrolens, and ring flash with two different cross-polarizing filters (Polar_eyes and Filtropolar), and without (Nonpolarizer; n = 7). The CIE L*a*b* color coordinates of digital images were calculated and remeasured with a spectroradiometer (SR). The color differences (ΔE00 ) between the SR and digital images were calculated and analyzed with the two-way analysis of variance (ANOVA) and Tukey HSD test (α = 0.05). ΔE00 values of all test groups were higher than the clinically acceptable threshold (∆E00 > 1.80). While the ∆E00 values of Filtropolar (6.19 ± 0.44) and Polar_eyes (7.82 ± 0.23) groups were significantly higher than the Nonpolarizer (4.69 ± 0.32) for the 1M1 shade tab, ∆E00 value of Polar_eyes (6.23 ± 0.34) was significantly lower than Nonpolarizer (10.71 ± 0.48) group for 5M3 shade tab (p < 0.05). The color-matching results of tested digital photography techniques with and without cross-polarization were unacceptable, compared to a spectroradiometer. While digital photography with Polar_eyes cross-polarizing filter has closer results to the reference device for the low-in-value shade table (5M3), for the high-in-value shade table (1M1), improved results were obtained without a cross-polarizing filter. The cross-polarization filters are increasingly used in dentistry for tooth color communication with digital photography techniques. However, the digital photography techniques with-without cross-polarization filterers should be improved to obtain clinically acceptable color-matching results.

Photogrammetry-Based 3D Textured Point Cloud Models Building and Rock Structure Estimation

Trace lines on the outcrop of a rock mass are usually the primary data source for the estimation of rock structure. It is important to obtain the data of trace lines precisely. Photogrammetry is well suited to finish this task. However, this is mainly conducted by commercial software, and not every researcher has easy access to the method of digital photogrammetry. This study aims to provide researchers with a low-cost method of building a photogrammetry-based textured 3D point cloud model (FMBPM) and display the applicability of the method to estimating the rock structure of rock masses. In the FMBPM, a digital single-lens reflex camera with a prime lens and a total station are the necessary hardware employed to capture images and measure the coordinates of feature points. A coordinate transformation means of converting model coordinates to physical coordinates was introduced. A program for calculating a joint orientation based on the coordinates of inflection points on the trace line of the joint was developed. A section of a rock slope was selected as a case to show the procedures and the practicability of the FMBPM. The textured 3D point cloud model of the rock slope was successfully built, and the rock structure of the rock slope was analyzed using the joint disk model generated based on the trace lines extracted from the point cloud model. The results show that: (1) the precision of the point coordinates of the textured 3D point cloud model could achieve 3.96 mm, taking the data of the total station as the reference; (2) the rock structure of the slope is good, according to the value of the rock quality designation; (3) the new method is applicable in engineering practices.

Use of scanning devices for object 3D reconstruction by photogrammetry and visualization in virtual reality

This article aims to compare two different scanning devices (360 camera and digital single lens reflex (DSLR) camera) and their properties in the three-dimensional (3D) reconstruction of the object by the photogrammetry method. The article first describes the various stages of the process of 3D modeling and reconstruction of the object. A point cloud generated to the 3D model of the object, including textures, is created in the following steps. The scanning devices are compared under the same conditions and time from capturing the image of a real object to its 3D reconstruction. The attributes of the scanned image of the recon-structed 3D model, which is a mandarin tree in a citrus greenhouse in a daylight environment, are also compared. Both created models are also compared visually. That visual comparison reveals the possibilities in the application of both scanning devices can be found in the process of 3D reconstruction of the object by photogrammetry. The results of this research can be applied in the field of 3D modeling of a real object using 3D models in virtual reality, 3D printing, 3D visualization, image analysis, and 3D online presentation.

Digital Photography versus Spectrophotometry Assessment ofColor Stability of Resin Composite

Purpose: To compare digital photography to spectrophotometry in evaluating the color stability of resin composite. Materials and methods: Thirty- two disc-like specimens of Filtek Z350 resin composite were prepared and color-assessed; before and after 30 days of submersion in coffee solution. For each specimen, color was assessed according to Commission Internationale de I’Eclairage (CIE) color space values using: Two different versions of Canon Digital Single Lens Reflex (DSLR) camera; with standard lenses, flash, and settings: Canon 600d (Group I) and Canon 1100d (Group II), and a digital spectrophotometer (Vita Easyshade advance 4.0; Vita Zahnfabrik, Bad Sackingen, Germany) as a control (group lll). Color change (ΔE) was recorded for individual devices, tabulated, and statistically analyzed using oneway ANOVA, then Tukey’s post hoc test (P ≤ 0.05). Results: Statistically, no significant difference appeared among the used devices (P≤ 0.05) while assessing the color stability of Filtek Z350 resin composite. Conclusions: Both devices are similarly valuable for color assessment of resin composite.

A joint validation study on camera-aided illuminance measurement

This joint study conducted in the United States and Japan reviewed existing illuminance measurement methods that use a conventional digital single-lens reflex camera, including (a) per-pixel illuminance calculation using non-fisheye wide-angle lenses, (b) hemispherical projection-based illuminance calculation, (c) the KU method developed by the University of Kansas (KU) and (d) the L-CEPT method developed by the Japanese team for per-pixel illuminance calculation using 180° fisheye lens. Next, laboratory and field measurements were conducted in 32 test scenarios in Kansas and Japan to improve and validate the two similar methods (c) and (d) for per-pixel illuminance calculation and compare them to the simplified method (b) using orthographic projection-based illuminance calculation. Based on the test results, the camera-aided illuminance measurement method could have an error rate of 13.7% ± 15.3% (SD) in all 32 scenarios. Large errors (&gt;25%) were observed in six extremely dynamic gymnasiums with rapidly changing morning sunlight. Alternatively, an average error rate of 7.7% ± 7.5% was observed in the 26 test scenarios without rapidly changing direct sunlight. The simplified orthographic projection-based method could achieve the same level of accuracy as the per-pixel KU/L-CEPT method. Yet, multiple issues on camera-aided illuminance measurement still need further investigation.

Comparison of marginal accuracy in two different materials used in provisional crown and bridge - an in vitro experimental study.

To determine the difference in the marginal accuracy at buccal, lingual, mesial and distal margins of temporary crowns fabricated with bisacryl-based temporary crown material. The in-vitro, experimental, laboratory-based study was conducted at the Aga Khan University, Karachi, from September to December 2019, and comprised two bisacryl-based temporary crown material, Integrity and Protemp 4, which were used to fabricate a sample of 24 temporary crowns. A pre-operative polyvinyl siloxane impression served as a template for temporary crown fabrication. A right mandibular molar tooth on a typodont was prepared to receive a crown. The provisional crown material was syringed onto the template and was allowed to cure. All four surfaces of the crown were observed under a stereomicroscope equipped with digital single-lens reflex camera at 25.6x magnification. An image of each surface was captured and a photographic record was maintained. An image processing software was used for the measurement of marginal discrepancy. Marginal accuracy among the four surfaces was assessed. Data was analysed using SPSS 23. Mean marginal discrepancy for provisional crowns fabricated with Protemp 4 and Integrity was 410±222μm and 319±176μm, respectively. The marginal discrepancy between the two groups was statistically significant (p=0.027), with buccal margin exhibiting the most discrepancy (p<0.01). Integrity showed less microleakage than Protemp 4. Among all the walls, the buccal wall showed the most microleakage. Marginal accuracy was found to be dependent upon the type of provisional crown material and the side of the prepared axial wall.

Evaluation and Comparison of the Geometrical Relationship of Tooth and Lip Arcs and Their Correlation to Smile Arcs Between Males and Females in a North Indian Population.

Background With the increasing influence of social media, millennials and the generations that follow haveincreasingly pressing aesthetic concerns. Following this, there has been a sea change in treatment plans and procedures as well as the choice of material. Dentistry nowadays is dependent on digital data to compute and design prostheses; these technologies are often not readily available all over the world. The purpose of this research article is to measure the tooth arc (TA) and lip arc (LA) and their correlation to the smile arcs with a cohort consisting of males and females from a single center in northern India. The SA measurement, evaluation, and comparison of smile aesthetics in this young population may be used as a threshold to these smile variables so that prosthodontists can easily prevent or modify aesthetically displeasing features. This research article will be useful for cases requiring restorations and replacements of maxillary anterior teeth. Materials and methods In this research work, photographic analysis was used and photographs of hundred subjects were taken. The camera was fixed using a tripod, at an 11-inch distance from the face, so that a clear picture of the face could be taken from the tip of the nose to the chin. A digital single-lens reflex (DSLR) camera (Nikon D-60, with the Nikon DX AF-S Nikkor 18- 135mm lens, Tokyo, Japan) was used to take the facial photographs.As the posed smile is more predictable than the natural smile, subjects were asked to smile while keeping their natural head position (NHP). Parabolas were made with Math-GV software () and superimposed on the photographs to calculate the value. Results The mean LA shows greater curvature in the female population. There was no significant (p=0.92) relationship between TA curvature in the male (0.07±0.03)and female populations (0.08 ± 0.03), whereas the LA in males (0.10±0.03)and LA in females (0.12±0.04) showed a significant relationship (p=0.03) between both groups. The LA of the female population was found to be steeper than that of the male population. This study signifies that there is no significant difference (p=0.92) between the skeletal makeup of themale and female populations but the muscular activity and muscle function differ in the male and female populations. Regarding arc-wise comparisons in both male and female populations, the male population showed a statistically insignificant (p=0.27) correlation in lip and tooth arcs. But in the female population, the correlation between these arcs was statistically significant (p=0.01). Conclusion These study results provide useful guidance for evaluating anterior teeth and planning treatment for aesthetic restorative care.Clinicians should consider not only racial and gender differences when developing an aesthetic treatment plan but also the symmetry of the facial structure which should be in harmony with the dental arc. The harmony of each determinant of aesthetics, with each other, aids in promoting beauty as a whole.

X-ray-acquired imaging and detection radiography system using digital radiography with a DSLR digital camera: preliminary results of a pilot study

This study aimed to develop an X-ray digital radiography (DR) imaging system with a low radiation dose and superior resolution compared to those of the existing computed radiography (CR) and DR image acquisition systems using a complementary metal–oxide-semiconductor (CMOS) sensor-type digital single-lens reflex (DSLR) camera that is capable of adjusting sensitivity. The X-ray system consists of an X-ray generator, a DSLR camera, and a power cable. The X-ray irradiated from the X-ray imaging device was detected on a fluorescence plate located on the upper part of the body, and an image was captured by a digital camera installed below the fluorescence plate. After converting the image into an electric signal inside the pixel, the data are output through a cable to the computer, which is a data-processing device installed outside the imaging system. The spatial resolution using the resolution chart was 3.19 (LP/mm). The plot profile obtained using the ImageJ program showed a spatial resolution difference according to the spatial frequency. In addition, by exposing X-rays to the resolution chart, a plot profile of 1.0–4.86 (LP/mm) was drawn for the surface profile and resolution according to spatial frequency. Using an aluminum step wedge, images from 3.0–18 mm and plot profiles were shown. In the phantom, the hand muscle signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were 13.42 was 7.2, and the bone SNR and CNR were 10.86 and 7.2%, respectively. In conclusion, the X-ray image acquisition system using a CMOS sensor-type DSLR camera has the advantage of acquiring images in real-time with low radiation dose, resolution, and contrast, so it applies to X-ray examination in clinical practice, such as the existing CR and DR image acquisition systems. DSLR image acquisition systems can be deployed in developing countries and provided through teleradiology and telemedicine.

A Simple Way to Reduce 3D Model Deformation in Smartphone Photogrammetry

Recently, the term smartphone photogrammetry gained popularity. This suggests that photogrammetry may become a simple measurement tool by virtually every smartphone user. The research was undertaken to clarify whether it is appropriate to use the Structure from Motion-Multi Stereo View (SfM-MVS) procedure with self-calibration as it is done in Uncrewed Aerial Vehicle photogrammetry. First, the geometric stability of smartphone cameras was tested. Fourteen smartphones were calibrated on the checkerboard test field. The process was repeated multiple times. These observations were found: (1) most smartphone cameras have lower stability of the internal orientation parameters than a Digital Single-Lens Reflex (DSLR) camera, and (2) the principal distance and position of the principal point are constantly changing. Then, based on images from two selected smartphones, 3D models of a small sculpture were developed. The SfM-MVS method was used, with self-calibration and pre-calibration variants. By comparing the resultant models with the reference DSLR-created model it was shown that introducing calibration obtained in the test field instead of self-calibration improves the geometry of 3D models. In particular, deformations of local concavities and convexities decreased. In conclusion, there is real potential in smartphone photogrammetry, but it also has its limits.

Implementation of a full-color holographic system using RGB-D salient object detection and divided point cloud gridding.

At present, a real objects-based full-color holographic system usually uses a digital single-lens reflex (DSLR) camera array or depth camera to collect data. It then relies on a spatial light modulator to modulate the input light source for the reconstruction of the 3-D scene of the real objects. However, the main challenges the high-quality holographic 3-D display faced were the limitation of generation speed and the low accuracy of the computer-generated holograms. This research generates more effective and accurate point cloud data by developing an RGB-D salient object detection model in the acquisition unit. In addition, a divided point cloud gridding method is proposed to enhance the computing speed of hologram generation. In the RGB channels, we categorized each object point into depth grids with identical depth values. The depth girds are divided into M × N parts, and only the effective parts will be calculated. Compared with traditional methods, the calculation time is dramatically reduced. The feasibility of our proposed approach is established through experiments.

LFIENet: Light Field Image Enhancement Network by Fusing Exposures of LF-DSLR Image Pairs

Plenoptic cameras can record both spatial and angular information of incident rays as 4D light field (LF) images, which have unique advantages in a wide range of computer vision and graphics applications. However, plenoptic cameras usually suffer from image quality degradation due to limited resolution, very small sub-apertures for sub-views, improper exposure and color quantization of image sensors. Raw macro-pixel LF images captured by plenoptic cameras are usually decomposed into an array of sub-views, during which decomposition and improper correction would further damage the quality of LF images. Therefore, the sub-views of an LF image always have tricky problems of low dynamic range, brightness reduction, color deviation and missing textural details in improper exposure areas due to the small sub-aperture for each sub-view. We observed that it is hard to tell that the brightness (tone) ranges of DSLR (Digital Single Lens Reflex) Camera images are always better than that of LF images even captured from the same real-world scenes. Thus, instead of directly taking the accompanying DSLR images as ground truths for enhancing LF images, we propose an unsupervised neural network, called LFIENet, for properly fusing the exposures of LF-DSLR image pairs. With the help of corresponding DSLR images, the enhanced LF images would contain much abundant textural details and have extended dynamic ranges and better contrast. Since histogram equalization enhancement for brightness range is able to extend dynamic range and improve image contrast, we propose a Histogram Equalization Attention Module (HEAM) to discover the over/under-exposed areas for properly fusing LF-DSLR image pairs. In addition, for learning the proposed neural network, we propose a real-world LF-DSLR image pair dataset. Extensive experiments on various challenging real-world LF images demonstrate the effectiveness of our network.

Rapid tunnel scanning using a 360-degree camera and SfM photogrammetry

Photogrammetric scanning can be employed for the digitization of underground spaces, for example for remote mapping, visualization, or training purposes. However, such a technique requires capturing many photos, which can be laborious and time-consuming. Previous research has demonstrated that the acquisition time can be reduced by capturing the data with multiple lenses or devices at the same time. Therefore, this paper demonstrates a method for rapid scanning of hard rock tunnels using Structure-from-Motion (SfM) photogrammetry and a 360-degree camera. The test was performed in the Underground Research Laboratory of Aalto University (URLA). The tunnel is located in granitic rocks at a depth of 20 m below the Otaniemi campus in Espoo, Finland. A 10 m long and 3.5 m high tunnel section with exposed rock was selected for this study. Photos were captured using the 360-degree camera from 27 locations and 3D models were reconstructed using SfM photogrammetry. The accuracy, speed, and resolution of the 3D models were measured and compared with models scanned with a digital single-lens reflex (DSLR) camera. The results show that the data capture process with a 360-degree camera is 6x faster compared to a conventional camera. In addition, the orientation of discontinuities was measured remotely from the 3D model and the digitally obtained values matched the manual compass measurements. Even though the quality of the 360-degree camerabased 3D model was visually inferior compared to the DSLR model, the point cloud had sufficient accuracy and resolution for semi-automatic discontinuity measurements. The quality of the models can be improved by combining 360-degree and DSLR photos which result in a point cloud with 3x higher resolution and 2x higher accuracy. The results demonstrated that 360-degree cameras can be used for the rapid digitization of underground tunnels.

Avian Diversity and Its Feeding Guilds in Respect to the Rural Landscape of District Barnala (Punjab)

Avian diversity is a strong indication of the stability and integrity of structure and processes in an ecosystem. Though birds are adapted to almost every habitat and breed on almost all the continents of the earth, the majority of birds are linked to the agro-ecosystem to survive as agriculture offers an extremely predictable and concentrated food source; and birds also play a role in nutrient cycling, soil formation, and energy transfer in the ecosystems. Therefore, from the perspective of environmental monitoring, the assessment of bird assemblages in various ecosystems is prioritized. Due to the intensification of agriculture, Punjab's agro-ecosystem has undergone tremendous changes. The present study on avian diversity in the rural agricultural landscape (RurekeKalan, Sekha, Sanghera, and Cheema) of district Barnala, Punjab has been conducted from March 2022 to May 2022 using a Digital SLR camera (Canon 1300 D) binoculars (Nikon A211 16X50) to observe the birds. Thirty species of birds belonging to twelve orders have been recorded, order Passeriformes being the most dominant one. Common Myna and Blue Rock Pigeon were found to be the most prevalent as compared to other bird species. Omnivory was found to be dominant as compared to other feeding habits. Although the present work is in no way conclusive, it serves to give an approximate understanding of the fauna in the study site and also reveals that agricultural intensification is a major concern for avian diversity conservation. The present study provides baseline data to understand the precise functions that different species of birds play in agro-ecosystems and for future study regarding conservation, habitat preferences, seasonal variations, nest ecology, breeding biology, etc. of the avian species that have been observed in the study region.

Estudio del patrón queiloscópico en alumnos de la Universidad Alfonso X El Sabio para la determinación de su sexo. estudio observacional transversal

Introduction: Cheiloscopy is as effective as dactyloscopy in identification methods because each person has a lip pattern distinguishable from others (unique, invariable, permanent and classifiable). The aim of this study is to identify the most frequent lip patterns in men and women using the Suzuki and Tsuchihashi classification, thus establishing a guide to verify the usefulness of this area in identification. Method: cross-sectional observational study (n=121), analysis of the lip pattern in the lower middle third of the lower third of the labia of the Suzuki and Tsuchihashi classification (I, I’, II, III, IV and V) with print on A4 paper and photographs Canon EOS 1300D (W) digital SLR camera with CMOS sensor with 18.0 megapixels. Double-blind and Chi squared statistical analysis was performed, with independent variable sex and dependent variable cheiloscopy path. Results: Regarding the total sample: women (n= 61; 50.41%) of type I; men (n= 28; 23.14%). Type I’ men (n=5; 6.05%), women (n=14; 16.94%). In type II we find in Type II and III in males the same proportion (n=2; 2.42%) and females in type II (3.63%) and type III (1.21%), Type V females (n=5; 6.05%), Males n= 0; in type IV there are no individuals with this pattern. There are no statistically significant differences between sex differentiation and cheiloscopic pattern, with a P&gt;0.05. Conclusions: There is weak evidence to be able to use cheiloscopy as a method of sex-cheiloscopic pattern differentiation. The predominant pattern in women is I, I’ and V, in men I and I’. There is no type IV and type V only occurs in women.

Detection of Coconut Clusters Based on Occlusion Condition Using Attention-Guided Faster R-CNN for Robotic Harvesting.

Manual harvesting of coconuts is a highly risky and skill-demanding operation, and the population of people involved in coconut tree climbing has been steadily decreasing. Hence, with the evolution of tree-climbing robots and robotic end-effectors, the development of autonomous coconut harvesters with the help of machine vision technologies is of great interest to farmers. However, coconuts are very hard and experience high occlusions on the tree. Hence, accurate detection of coconut clusters based on their occlusion condition is necessary to plan the motion of the robotic end-effector. This study proposes a deep learning-based object detection Faster Regional-Convolutional Neural Network (Faster R-CNN) model to detect coconut clusters as non-occluded and leaf-occluded bunches. To improve identification accuracy, an attention mechanism was introduced into the Faster R-CNN model. The image dataset was acquired from a commercial coconut plantation during daylight under natural lighting conditions using a handheld digital single-lens reflex camera. The proposed model was trained, validated, and tested on 900 manually acquired and augmented images of tree crowns under different illumination conditions, backgrounds, and coconut varieties. On the test dataset, the overall mean average precision (mAP) and weighted mean intersection over union (wmIoU) attained by the model were 0.886 and 0.827, respectively, with average precision for detecting non-occluded and leaf-occluded coconut clusters as 0.912 and 0.883, respectively. The encouraging results provide the base to develop a complete vision system to determine the harvesting strategy and locate the cutting position on the coconut cluster.

Studying flowers in 3D using photogrammetry.

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.

Location of Latent Forensic Traces Using Multispectral Bands

In this paper, a conventional camera modified to capture multispectral images, has been used to locate latent forensic traces with a smart combination of wavelength filters, capturing angle, and illumination sources. There are commercial multispectral capture devices adapted to the specific tasks of the police, but due to their high cost and operation not well adapted to the field work in a crime scene, they are not currently used by forensic units. In our work, we have used a digital SLR camera modified to obtain a nominal sensitivity beyond the visible spectrum. The goal is to obtain forensic evidences from a crime scene using the multispectral camera by an expert in the field knowing which wavelength filters and correct illumination sources should be used, making visible latent evidences hidden from the human-eye. In this paper, we show a procedure to retrieve from latent forensic traces, showing the validity of the system in different real cases (blood stains, hidden/erased tattoos, unlocking patterns on mobile devices). This work opens the possibility of applying multispectral inspections in the forensic field specially for operational units for the location of latent through non-invasive optical procedures.

Production of orthophoto map using mobile photogrammetry and comparative assessment of cost and accuracy with satellite imagery for corridor mapping: a case study in Manesar, Haryana, India

ABSTRACT The study aims to find a low-cost alternate technology to get imagery, using mobile platform, and produce digital orthophoto for corridor mapping, with a higher degree of accuracy and which can reduce the lag time of acquisition of data. The present study uses digital single-lens reflex cameras, mounted on a mobile vehicle, and acquisition of data in the video format rather than still photographs, as traditionally used in mobile mapping systems. The videos are used to create a set of images and orthophotos. A widespread ground control points were recorded in the study area, using the global navigation satellite system receiver, which measured the control points in real-time kinematic mode. Generation of digital orthophoto has been completed using the captured mobile imagery and ground control point. Furthermore, procurement of satellite imagery and aerial triangulation using ground control points have been done. While comparing the planimetric accuracy of orthophoto against satellite imagery using the ground control points, the achieved root mean square error value of produced orthophoto is 0.171 m in X axis and 0.205 m in Y axis. However, for Cartosat -1 satellite imagery, the RMSE value for X is 1.22 m and for Y is 1.98 m. This research proposes the alternate low-cost mobile mapping method to capture the imagery for orthophoto production. The cost of orthophoto production from mobile image was found 77% cheaper than the orthophoto cost from fresh/latest satellite imagery procurement, while the overall production was 70% cost-effective than the orthophoto maps made from archived imagery.

Spallation of Carbon Ablators in Arcjet Facility Experiments

Spallation is the mostly undesirable phenomenon where solid particles are ejected from ablative materials leaving less mass to be decomposed at the ablator surface. The exact mechanisms and conditions that promote spallation as well as the extent of it are unclear to this date. This paper presents the results of an extensive test campaign targeted at measuring spallation of carbonaceous ablator materials in an arc heated air flow of . The employed diagnostic methods are photogrammetric surface measurements, high-speed imaging, thermography, and two-color-ratio pyrometry using the raw digital single-lens reflex camera images from the photogrammetry setup. Data from the high-speed camera show a much higher spallation rate for the carbon preform Calcarb than for carbon-phenolic ablators. Temperature measurements show a difference of up to 300 K between carbon fibers and surrounding matrix. The pyrolysis gas from the phenolic resin is found to decrease the spallation rate of the carbon-phenolic ablator ZURAM compared to Calcarb, and the pyrolysis gas pressure slightly increases the distance that particles travel upstream after ejection from the front surface.

Rapid Photogrammetry with a 360-Degree Camera for Tunnel Mapping

Structure-from-Motion Multi-View Stereo (SfM-MVS) photogrammetry is a viable method to digitize underground spaces for inspection, documentation, or remote mapping. However, the conventional image acquisition process can be laborious and time-consuming. Previous studies confirmed that the acquisition time can be reduced when using a 360-degree camera to capture the images. This paper demonstrates a method for rapid photogrammetric reconstruction of tunnels using a 360-degree camera. The method is demonstrated in a field test executed in a tunnel section of the Underground Research Laboratory of Aalto University in Espoo, Finland. A 10 m-long tunnel section with exposed rock was photographed using the 360-degree camera from 27 locations and a 3D model was reconstructed using SfM-MVS photogrammetry. The resulting model was then compared with a reference laser scan and a more conventional digital single-lens reflex (DSLR) camera-based model. Image acquisition with a 360-degree camera was 3× faster than with a conventional DSLR camera and the workflow was easier and less prone to errors. The 360-degree camera-based model achieved a 0.0046 m distance accuracy error compared to the reference laser scan. In addition, the orientation of discontinuities was measured remotely from the 3D model and the digitally obtained values matched the manual compass measurements of the sub-vertical fracture sets, with an average error of 2–5°.