Landmark Visibility Research Articles

Changes in movement patterns in relation to sun conditions and spatial scales in wild western gorillas.

For most primates living in tropical forests, food resources occur in patchworks of different habitats that vary seasonally in quality and quantity. Efficient navigation (i.e., spatial memory-based orientation) towards profitable food patches should enhance their foraging success. The mechanisms underpinning primate navigating ability remain nonetheless mostly unknown. Using GPS long-term tracking (596days) of one group of wild western lowland gorillas (Gorilla gorilla gorilla), we investigated their ability to navigate at long distances, and tested for how the sun was used to navigate at any scale by improving landmark visibility and/or by acting as a compass. Long episodic movements ending at a distant swamp, a unique place in the home range where gorillas could find mineral-rich aquatic plants, were straighter and faster than their everyday foraging movements relying on spatial memory. This suggests intentional targeting of the swamp based on long-distance navigation skills, which can thus be efficient over a couple of kilometres. Interestingly, for both long-distance movements towards the swamp and everyday foraging movements, gorillas moved straighter under sunlight conditions even under a dense vegetation cover. By contrast, movement straightness was not markedly different when the sun elevation was low (the sun azimuth then being potentially usable as a compass) or high (so providing no directional information) and the sky was clear or overcast. This suggests that gorillas navigate their home range by relying on visual place recognition but do not use the sun azimuth as a compass. Like humans, who rely heavily on vision to navigate, gorillas should benefit from better lighting to help them identify landmarks as they move through shady forests. This study uncovers a neglected aspect of primate navigation. Spatial memory and vision might have played an important role in the evolutionary success of diurnal primate lineages.

Accuracy and repeatability of fetal facial measurements in 3D ultrasound: A longitudinal study

ObjectiveFetal face measurements in prenatal ultrasound can aid in identifying craniofacial abnormalities in the developing fetus. However, the accuracy and reliability of ultrasound measurements can be affected by factors such as fetal position, image quality, and the sonographer's expertise. This study assesses the accuracy and reliability of fetal facial measurements in prenatal ultrasound. Additionally, the temporal evolution of measurements is studied, comparing prenatal and postnatal measurements. MethodsThree different experts located up to 23 facial landmarks in 49 prenatal 3D ultrasound scans from normal Caucasian fetuses at weeks 20, 26, and 35 of gestation. Intra- and inter-observer variability was obtained. Postnatal facial measurements were also obtained at 15 days and 1 month postpartum. ResultsMost facial landmarks exhibited low errors, with overall intra- and inter-observer errors of 1.01 mm and 1.60 mm, respectively. Landmarks on the nose were found to be the most reliable, while the most challenging ones were those located on the ears and eyes. Overall, scans obtained at 26 weeks of gestation presented the best trade-off between observer variability and landmark visibility. The temporal evolution of the measurements revealed that the lower face area had the highest rate of growth throughout the latest stages of pregnancy. ConclusionsCraniofacial landmarks can be evaluated using 3D fetal ultrasound, especially those located on the nose, mouth, and chin. Despite its limitations, this study provides valuable insights into prenatal and postnatal biometric changes over time, which could aid in developing predictive models for postnatal measurements based on prenatal data.

Evaluating Pelvic Tilt Using the Pelvic Antero-Posterior Projection Images: A Systematic Review

BackgroundPelvic tilt (PT) is a routinely evaluated parameter in hip and spine surgeries, and is usually measured on a sagittal pelvic radiograph. This may not always be feasible due to limitations such as landmark visibility, pelvic anomaly, and hardware presence. Tremendous efforts have been dedicated to using pelvic antero-posterior (AP) radiographs for assessing sagittal PT. Thus, this systematic review aimed to collect these methods and evaluate their performances. MethodsTwo independent reviewers searched the PubMed, Ovid, Cochrane, and Web of Science databases in June 2023 with backward reference trailing (Google Scholar archive). There were 30 studies recruited. Risk of bias was assessed using the prediction model risk of bias assessment tool. The relevant data were tabulated in a standardized form for evaluating either the absolute PT or relative PT. Disagreement was resolved by discussing with the senior author. ResultsThere were 19 parameters from pelvic AP projection images involved, with 4 studies which used artificial intelligence, eyeball, or statistical shape method not involving a specific parameter. In comparing the PT values from pelvic sagittal images with those extrapolated from antero-posterior projection images, the highest correlation coefficient was found to be 0.91. The mean absolute difference (error) was 2.6°, with a maximum error reaching 10.9°. Most studies supported the feasibility of using AP parameters to calculate changes in PT. ConclusionsNo individual AP parameter was found to precisely estimate absolute PT. However, relative PT can be derived by evaluating serial AP radiographs of a patient in varying postures, employing any AP parameters.

Structural Landmark Salience Computation in Compact Urban Districts with 3D Node-Landmark Grid Analysis Model: A Case Study on Two Sample Districts in Changsha, China

Mastering the relationship between urban landmarks and urban space morphology in urban planning, landscape planning, and architectural design helps maintain the intelligibility of compact urban districts. The objective of the present study was to numerically determine the structural salience of various landmarks in an urban environment and use it to interpret the intelligibility of the city. Combining the measurement method of 3D visibility and the related principles of space syntax, this study develops a new 3D Node–Landmark Grid Analysis Model (3D NL GAM) for structural salience computation of urban landmarks. In this study, a numerical approach is used to construct a 3D simulation model. Firstly, the visibility of each decision node to landmarks in an urban environment, using a 3D digital model, is measured using the 3D isovist component of Rhinoceros and Grasshopper software. Secondly, links among wayfinding decision nodes and landmarks are established to form a 3D NL GAM. The normalized angular integration of decision nodes and the normalized angular choice of landmarks are computed using the principle of space syntax. Thirdly, the structural salience of landmarks is determined with a function of landmark visibility, spatial properties of landmarks, and wayfinding decision nodes. Finally, a case study was carried out by using a 3D NL GAM to analyze three types of urban areas located in Changsha. The results indicated that large-scale natural landscapes have a higher structural salience among the types of landmarks. The structural salience of architectural landmarks in the combined spatial form of combining tall and low building groups has a clear advantage over the form dominated by high-rise building groups. Raising the height of landmark buildings can modify the structure of the grid analysis model and improve the people aggregation of urban space. The 3D NL GAM can quantify the spatial properties and landmark structural salience of a city and can effectively assist in the evaluation of the intelligibility of built or future urban environments.

Diagnostic compatibility of various fixed orthodontic retainers for head/neck MRI and dental MRI

ObjectivesTo evaluate the diagnostic MRI compatibility of different fixed orthodontic retainers using a high-resolution 3D-sequence optimized for artifact reduction.Materials and methodsMaxillary and mandibular retainers made of five different materials were scanned in vitro and in vivo at 3 T MRI using an MSVAT-SPACE sequence. In vitro, artifact volumes were determined for all maxillary and mandibular retainers (AVmax; AVmand). In vivo, two independent observers quantified the extent of artifacts based on the visibility of 124 dental and non-dental landmarks using a five-point rating scale (1 = excellent, 2 = good, 3 = acceptable, 4 = poor, 5 = not visible).ResultsRectangular-steel retainers caused the largest artifacts (AVmax/AVmand: 18,060/15,879 mm3) and considerable diagnostic impairment in vivo (mean landmark visibility score ± SD inside/outside the retainer areas: 4.8 ± 0.8/2.9 ± 1.6). Smaller, but diagnostically relevant artifacts were observed for twistflex steel retainers (437/6317 mm3, 3.1 ± 1.7/1.3 ± 0.7). All retainers made of precious-alloy materials produced only very small artifact volumes (titanium grade 1: 70/46 mm3, titanium grade 5: 47/35 mm3, gold: 23/21 mm3) without any impact on image quality in vivo (each retainer: visibility scores of 1.0 ± 0.0 for all landmarks inside and outside the retainer areas).ConclusionsIn contrast to steel retainers, titanium and gold retainers are fully compatible for both head/neck and dental MRI when using MSVAT-SPACE.Clinical relevanceThis study demonstrates that titanium and gold retainers do not impair the diagnostic quality of head/neck and dental MRI when applying an appropriate artifact-reduction technique. Steel retainers, however, are not suitable for dental MRI and can severely impair image quality in head/neck MRI of the oral cavity.

LiDAR-based method for analysing landmark visibility to pedestrians in cities: case study in Kraków, Poland

ABSTRACT We propose a method for analysing landmark visibility from a pedestrian’s perspective. A case study is performed in Kraków, a city with many architectural monuments, where airborne LiDAR is used to model both buildings and urban greenery. The proposed method involves preliminary and detailed stages. The preliminary stage entails an inverse analysis (I–Vis) that departs from the typical visibility analysis to enable the use of landmarks as observers instead of targets. I–Vis results in paths with high landmark visibility. The detailed stage involves the use of a virtual panorama (V-Pan) to determine the visual exposure of the landmarks. Landmarks considered visible by I–Vis are generally consistent with landmarks identified by V-Pan. Discrepancies occur when trees appear in the near field-of-view. In addition, the accuracy of the skyline length and visible landmark surface area is evaluated against ground observations. The obtained results show that V-Pan can evaluate landmark visibility with an accuracy of approximately 75%. The key contributions of the work to visibility analysis of urban landmarks are in the inverse viewshed strategy and evaluation of the visual exposure parameters on LiDAR virtual panoramas.

Non-Contact Respiration Monitoring and Body Movements Detection for Sleep Using Thermal Imaging.

Monitoring of respiration and body movements during sleep is a part of screening sleep disorders related to health status. Nowadays, thermal-based methods are presented to monitor the sleeping person without any sensors attached to the body to protect privacy. A non-contact respiration monitoring based on thermal videos requires visible facial landmarks like nostril and mouth. The limitation of these techniques is the failure of face detection while sleeping with a fixed camera position. This study presents the non-contact respiration monitoring approach that does not require facial landmark visibility under the natural sleep environment, which implies an uncontrolled sleep posture, darkness, and subjects covered with a blanket. The automatic region of interest (ROI) extraction by temperature detection and breathing motion detection is based on image processing integrated to obtain the respiration signals. A signal processing technique was used to estimate respiration and body movements information from a sequence of thermal video. The proposed approach has been tested on 16 volunteers, for which video recordings were carried out by themselves. The participants were also asked to wear the Go Direct respiratory belt for capturing reference data. The result revealed that our proposed measuring respiratory rate obtains root mean square error (RMSE) of bpm. The advantage of this approach lies in its simplicity and accessibility to serve users who require monitoring the respiration during sleep without direct contact by themselves.

Landmarks as Cultural Heritage Assets Affecting the Distribution of Settlements in Rural Areas—An Analysis Based on LIDAR DTM, Digital Photographs, and Historical Maps

The final decision of the owner of the plot who plans to build a house depends on many factors most of which are of legal and financial nature. The authors demonstrate that the decisions regarding specific location within the plot of land are influenced by intangible components as well, namely the intention to have the best view. The view is often related to the occurrence of landmarks with prominent visual impact in the landscape that determine visual connections. The rural landscape is determined by the spatial arrangement including the buildings, the shape of public spaces, ownership divisions, and the land distribution. Being an element of rural cultural heritage, the arrangement of buildings is influenced by a vast number of factors such as geographical, historical, physical, and socio-economic ones. This article focuses on determining the interaction between the settlement locations and zones with an excellent, unique view of characteristic, well-known architectural landmarks. Mapping of viewsheds of many features is a critical element of the landscape planning process and facilitates the protection of cultural heritage assets. The analysis involved LiDAR DTM (Digital Terrain Model created in Light Detection and Ranging technology), digital photographs, and historical maps. In terms of the administrative subdivision, the area comprises 20 localities. The landmark visibility analysis for locations of the buildings covered a 140 km2 area of Carpathian Foothills in southern Poland. The article combines experiences in the field of landscape architecture, spatial planning and the use of Geographic Information System (GIS) technology. The examples show that the modern development layout refers to the historical structure and the development of a new settlement tissue has a cultural background and is influenced by spatial landmarks.

Maintaining Visibility of a Landmark using Optimal Sampling-based Path Planning

An approach to extend sampling-based path planning algorithms to include visual restrictions is presented. This approach imposes of visual constraints during the sampling and optimization processes. Four visual constraints are imposed during sampling: 1) keep the landmark within the sensor field of view, 2) avoid landmark occlusions, 3) maintaining landmark features near the image center, and 4) limit changes in landmark view orientation. These last two are imposed during path optimization. The robot task is to maintain these constraints, in an environment with obstacles, while the robot changes configurations. The sampling-based motion planning algorithm imposes and maintains both physical and visual restrictions. The process uses a collision checker to detect self-and obstacle-collisions, or landmark occlusions. To infer the landmark visibility, the algorithm dynamically builds a 3D model of camera field visibility as seen from the moving robot. To maintaining the landmark features close to the image center, a distance parameter from the field of view boundary to the landmark is used and optimized. The camera roll angle was included as another element to be optimized, limiting changes in orientation. The algorithm has been implemented, and both results in simulation and experiments using a real robot manipulator are presented.

A Revisiting Method Using a Covariance Traveling Salesman Problem Algorithm for Landmark-Based Simultaneous Localization and Mapping.

This paper presents an efficient revisiting algorithm for landmark-based simultaneous localization and mapping (SLAM). To reduce SLAM uncertainty in terms of a robot’s pose and landmark positions, the method autonomously evaluates valuable landmarks for the data associations in the SLAM algorithm and selects positions to revisit by considering both landmark visibility and sensor measurement uncertainty. The optimal path among the selected positions is obtained by applying the traveling salesman problem (TSP) algorithm. To plan a path that reduces overall uncertainty, the cost matrix associated with the change in covariance between all selected positions of all pairs is applied for the TSP algorithm. From simulations, it is verified that the proposed method efficiently reduces and maintains SLAM uncertainty at the low level compared to the backtracking method.

Ultrasound-guided L5 dorsal ramus block: validation of a novel technique

BackgroundAlthough the value of ultrasound-guided (USG) lumbar medial branch blocks (MBB) has previously been examined in several clinical trials, blocking the L5 dorsal ramus (DR) remains a technical challenge and...

Classification of cityscape areas according to landmarks visibility analysis

The paper introduces a method of computational analysis of cityscape called Weighted Visual Exposure Map (WVEM). The method aims at supporting the process of examining attractive vistas in a city. The value of a vista is calculated for each point of the city. The assessment depends on the visibility of selected landmarks that are the most important for the image of a city. The WVEM algorithm includes: a) number of landmarks that can be seen from a given point; b) range of vertical exposure of each landmark; and c) individual weight reflecting the importance of a landmark for the cityscape. The more landmarks can be seen from a given location, the higher the value of the vista. The WVEM calculation process aims at showing the distribution of the most valuable locations in the city. The result is geometrically unequivocal. It depends on initial assumptions (selection and parameters of landmarks) and 3D city model used. The study presented WVEM analyses based on the Digital Surface Model (DSM) that was suitable for the architectural scale (0.5 m grid) for the area in excess of 20km2. The landmark visibility analysis used the Visual Impact Size (VIS) method. The VIS application and WVEM emulation were based on software developed by the authors (C++). Guidelines how to apply the WVEM method for other places and using other software was also discussed. The WVEM method can be used in spatial planning to support the process of determining strategic vistas. This can be a starting point for defining principles of cityscape protection and development.

Overcoming challenges in developing more usable pedestrian navigation systems

ABSTRACTThis article presents an overview of a research project focusing on improving the usability of pedestrian navigation systems by following a User-Centered Design (UCD) approach. One of the main problems with those systems is how to adequately support and enhance the spatial interactions of a traveler to new urban areas, which is crucial for successful self-orienting and wayfinding. The methodology employed allows for conceptualizing, implementing and evaluating research prototypes that aim to satisfy the special user requirements. Outlined in this article are the techniques designed and integrated in the developed prototype, the methods used for their evaluation through field-based studies and the challenges encountered during this process. New techniques with a measurable impact on the effectiveness, efficiency and satisfaction of navigation were tested and found to dramatically enhance the sense of personal geo-identification in new places. Examples of those techniques are landmark visibility indication, multi-path routing based on time availability, multi-perspective landmark photos and reverse overview + detail maps. Overall, the outcomes of this research verify the capacity of UCD to help overcoming current usability issues with pedestrian navigation systems. By demonstrating an effective UCD methodology and discussing the lessons learned, we intend to aid the development of next generation navigation appliances.

Content vs. Context

Due to the ubiquity of sensor-equipped smartphones, it has become increasingly feasible for users to capture videos together with associated geographic metadata, for example the location and the orientation of the camera. Such contextual information creates new opportunities for the organization and retrieval of geo-referenced videos. In this study we explore the task of landmark retrieval through the analysis of two types of state-of-the-art techniques, namely media-content-based and geocontext-based retrievals. For the content-based method, we choose the Spatial Pyramid Matching (SPM) approach combined with two advanced coding methods: Sparse Coding (SC) and Locality-Constrained Linear Coding (LLC). For the geo-based method, we present the Geo Landmark Visibility Determination (GeoLVD) approach which computes the visibility of a landmark based on intersections of a camera's field-of-view (FOV) and the landmark's geometric information available from Geographic Information Systems (GIS) and services. We first compare the retrieval results of the two methods, and discuss the strengths and weaknesses of each approach in terms of precision, recall and execution time. Next we analyze the factors that affect the effectiveness for the content-based and the geo-based methods, respectively. Finally we propose a hybrid retrieval method based on the integration of the visual (content) and geographic (context) information, which is shown to achieve significant improvements in our experiments. We believe that the results and observations in this work will enlighten the design of future geo-referenced video retrieval systems, improve our understanding of selecting the most appropriate visual features for indexing and searching, and help in selecting between the most suitable methods for retrieval based on different conditions.

The influence of reference acceptance and reuse on conversational memory traces.

Not all pieces of information mentioned during an interaction are equally accessible in speakers' conversational memory. The current study sought to test whether 2 basic features of dialogue management (reference acceptance and reuse) affect reference recognition. Dyads of speakers were asked to discuss a route for an imaginary person, thus referring to the landmarks to be encountered. The results revealed that the participants' conversational memory for the references produced during the interaction depended on whether these had been reused during the interaction and by whom, along with landmark visibility during the interaction. These findings have implications for partner adaptation in dialogue, which depends in part on what speakers remember of past interactions.

Motion planning for maintaining landmarks visibility with a differential drive robot

This work studies the interaction of non-holonomic and visibility constraints using a Differential Drive Robot (DDR) that has to keep static landmarks in sight in an environment with obstacles. The robot has a limited sensor, namely, it has a restricted field of view and bounded sensing range (e.g. a video camera). Here, we mean by visibility that a clear line of sight can be thrown between the landmark and the sensor mounted on the DDR. We first determine the necessary and sufficient conditions for the existence of a path such that our system is able to maintain one given landmark visibility in the presence of obstacles. This is done through a recursive, complete algorithm that uses motion primitives exhibiting local optimality, as they are locally shortest-lengths paths. Then, we extend this result to the problem of planning paths guaranteeing visibility among a set of landmarks, e.g. to observe a given sequence of landmarks or to observe at each point of the path at least one element of the landmarks set. We also provide a procedure that computes the robot controls yielding such a path.11A preliminary version of this work has been presented in the 2008 International Workshop on the Algorithmic Foundations of Robotics (WAFR’08) and published in [1].

Increasing the Usability of Pedestrian Navigation Interfaces by means of Landmark Visibility Analysis

Communicating location-specific information to pedestrians is a challenging task which can be aided by user-friendly digital technologies. In this paper, landmark visibility analysis, as a means for developing more usable pedestrian navigation systems, is discussed. Using an algorithmic framework for image-based 3D analysis, this method integrates a 3D city model with identified landmarks and produces raster visibility layers for each one. This output enables an Android phone prototype application to indicate the visibility of landmarks from the user's actual position. Tested in the field, the method achieves sufficient accuracy for the context of use and improves navigation efficiency and effectiveness.

The impact of neuroendoscopy in the emergency setting—A retrospective study of imaging, intraoperative findings, and surgical outcome in 55 patients

Objectives To assess whether neuroendoscopy is an improved and effective diagnostic as well as therapeutic tool in the emergency setting compared with neuroimaging studies. Patients and Methods Sixty-two preoperative computed tomography (CT) and magnetic resonance (MR) scans from 55 adult patients admitted in the emergency ward were compared with equal number of neuroendoscopy observations by independent observers, who included cases of raised intracranial pressure related to hydrocephalus, shunt dysfunction, intracranial cysts, brain tumours, subdural effusions, etc. Results According to the results obtained, three groups were formed. Postoperative findings matched CT/MR images in 38.7% of all the procedures (Group 1). In 25.8%, neuroimages were different from endoscopy findings, nevertheless the differences did not justify any modification in the original surgical approach (Group 2). Finally, differences between endoscopical and preoperative studies in 34.48% of the procedures did justify modifications in the surgical plan (Group 3). Extensive fibrosis within the ventricular system associated with poor anatomic landmark visibility was found to be the main cause of surgical modification in the majority of these cases. Conclusions Usefulness of neuroendoscopy to increase the accuracy of intraoperative diagnosis, and therefore modify the surgical procedure in an emergency setting, is stressed.

An observer study: comparison of computed radiography to electronic and film portal imaging

Introduction: Computed radiography (CR) is an imaging facility that does not require the use of hard copy film, digital images are obtained with a photostimulable phosphor plate, which replaces film, in a cassette. As the first UK radiotherapy site to trial CR, we are collecting data to assess the feasibility of using CR in radiotherapy treatment verification.Method: From 30 patients undergoing radical radiotherapy, 10 were consecutively accrued to three sites: pelvis, thorax and head and neck. Treatment verification images were taken using current protocols, but substituting standard imaging for CR images on one fraction. Four independent observers were used: two clinical oncologists and two therapy radiographers. Observers rated CR, electronic portal imaging (EPI) and enhanced contrast (EC) films of the three sites for both landmark visibility and ease of verification decision, using a numerical scoring system.Results: Ratings for visibility of landmarks and for verification decision were similar for CR and film/EPI images for most landmarks. However, CR images rated poorly compared to EC film in the head and neck region with landmarks such as thyroid cartilage and cricoid cartilage rating as ‘not clear’. CR images rated better than EPI images for both visibility and verification decision on the majority of landmarks in the pelvis region.Conclusion: Results gathered from a relatively small sample size have provided the following conclusion. The visibility of landmarks in CR images is comparable to that in film and EPI. Verification of treatment images based on CR is comparable to that of the current imaging media in the department.

TreeJuxtaposer

Structural comparison of large trees is a difficult task that is only partially supported by current visualization techniques, which are mainly designed for browsing. We present TreeJuxtaposer, a system designed to support the comparison task for large trees of several hundred thousand nodes. We introduce the idea of "guaranteed visibility", where highlighted areas are treated as landmarks that must remain visually apparent at all times. We propose a new methodology for detailed structural comparison between two trees and provide a new nearly-linear algorithm for computing the best corresponding node from one tree to another. In addition, we present a new rectilinear Focus+Context technique for navigation that is well suited to the dynamic linking of side-by-side views while guaranteeing landmark visibility and constant frame rates. These three contributions result in a system delivering a fluid exploration experience that scales both in the size of the dataset and the number of pixels in the display. We have based the design decisions for our system on the needs of a target audience of biologists who must understand the structural details of many phylogenetic, or evolutionary, trees. Our tool is also useful in many other application domains where tree comparison is needed, ranging from network management to call graph optimization to genealogy.