We propose a camera model for line-scan cameras with telecentric lenses. The camera model assumes a linear relative motion with constant velocity between the camera and the object. It allows to model ...lens distortions, while supporting arbitrary positions of the line sensor with respect to the optical axis. We comprehensively examine the degeneracies of the camera model and propose methods to handle them. Furthermore, we examine the relation of the proposed camera model to affine cameras. In addition, we propose an algorithm to calibrate telecentric line-scan cameras using a planar calibration object. We perform an extensive evaluation of the proposed camera model that establishes the validity and accuracy of the proposed model. We also show that even for lenses with very small lens distortions, the distortions are statistically highly significant. Therefore, they cannot be omitted in real-world applications.
Knowledge about the interior and exterior camera orientation parameters is required to establish the relationship between 2D image content and 3D object data. Camera calibration is used to determine ...the interior orientation parameters, which are valid as long as the camera remains stable. However, information about the temporal stability of low-cost cameras due to the physical impact of temperature changes, such as those in smartphones, is still missing. This study investigates on the one hand the influence of heat dissipating smartphone components at the geometric integrity of implemented cameras and on the other hand the impact of ambient temperature changes at the geometry of uncoupled low-cost cameras considering a Raspberry Pi camera module that is exposed to controlled thermal radiation changes. If these impacts are neglected, transferring image measurements into object space will lead to wrong measurements due to high correlations between temperature and camera's geometric stability. Monte-Carlo simulation is used to simulate temperature-related variations of the interior orientation parameters to assess the extent of potential errors in the 3D data ranging from a few millimetres up to five centimetres on a target in X- and Y- direction. The target is positioned at a distance of 10 m to the camera and the Z-axis is aligned with camera's depth direction.
Research on parental sensitivity often relies on video observation of parent–infant dyads. However, to date, no study has assessed both infants’ and parents’ interactions with the camera, and how ...this relates to parental sensitivity levels. This exploratory study micro‐coded camera‐related behaviors (CRB) by 4‐month olds and their mothers and fathers on a 1‐s time base, and examined the associations between those behaviors and parental sensitivity in 75 Dutch families. While parents’ CRB made up only 0.8% of total interaction time, infants’ made up 12%. Multi‐level time‐series analyses showed that infants’ CRB predicted mothers’. Infants’ CRB predicted fathers’ CRB, and vice versa. Maternal sensitivity was significantly lower when children looked at the camera for over one‐third of total interaction time (Cohen's d = 1.26). These findings indicate further research is required to better understand how video observation might threaten ecological validity.
Ecological studies often require observations of animals and their behaviour. Motion‐activated cameras (camera traps) based on passive infrared detection (PIR) are a popular solution for recording ...animal activity in situations when it is impractical for humans to make sufficient observations. However, the reliability of these cameras for recording smaller vertebrates remains uncertain. We assessed the reliability of two widely used PIR camera traps (Bushnell 119740 and Moultrie 13068) for detecting small vertebrates. Specifically, we tested the effects of (1) camera trap model, (2) camera–subject distance and (3) animal class and size on the probability of detection. Brown rats moving across the ground were detected by the Bushnell camera with >80% probability at camera–subject distances ranging from 60 cm to 2 m, while the Moultrie camera was less efficient at distances >1 m. The probability of the Bushnell camera detecting birds feeding on flowers decreased from c. 80% at distances of 40–60 cm to <10% at 2 m and beyond. Larger birds (>20 g) were more likely to be detected than smaller birds (<15 g). Close‐focusing lenses on the Bushnell camera readily allow identification of individual bird species. These results help to establish guidelines for camera trap selection and placement in ecological studies of small terrestrial mammals and birds.
Camera traps allow animal activity to be recorded when it is impractical for humans to make observations. Close‐focusing camera traps allow identification of small vertebrates, but the triggering reliability of these cameras has not been thoroughly tested. We found that close‐focusing camera traps can reliably record activity of rats at distances of up to 2 m, but should be no more than 40–60 cm from small nectar‐feeding birds for triggering to be reliable.
Video analytics will drive a wide range of applications with great potential to impact society. A geographically distributed architecture of public clouds and edges that extend down to the cameras is ...the only feasible approach to meeting the strict real-time requirements of large-scale live video analytics.
Motion‐sensitive cameras are commonly used to monitor wildlife occupancy rates; however, few studies have assessed whether data from cameras are correlated with density estimates obtained from more ...traditional labor‐intensive methods such as those based on capture‐mark‐recapture. We used data from a boreal forest community to test whether camera data were correlated with densities estimated from independent monitoring methods. We placed 72 covert cameras in the forest around Lhù'ààn Mân' (Kluane Lake), Yukon, Canada, for 7 years and tracked changes in population densities by camera hit rates. We independently estimated population densities of snowshoe hares (Lepus americanus) and red squirrels (Tamiasciurus hudsonicus) using capture‐mark‐recapture via live trapping, and Canada lynx (Lynx canadensis), coyotes (Canis latrans), and moose (Alces americanus) by snow track transects. Density estimates obtained from conventional aerial surveys were also periodically available for moose. Except for red squirrels, camera hit rates were highly correlated with population density estimates obtained by traditional methods, including across a large range of estimated densities corresponding to cyclic population dynamics in several species. Accordingly, we infer that motion‐sensitive cameras could supplement or replace traditional methods for monitoring key species in boreal forest food webs. Using cameras to monitor population change has several advantages; they require less effort in the field, are non‐invasive compared to live‐trapping, include multiple species at the same time, and rely less on weather than either aerial surveys or snow track transects. Tracking changes across the vast boreal forest is becoming increasingly necessary because of climate and landscape change and our data validate the use of motion‐sensitive cameras to provide a useful quantitative method for state‐of‐the‐environment reporting.
We used data from a Yukon boreal forest community to test whether motion‐sensitive camera data were correlated with density estimated from independent monitoring. Camera hit rates were highly correlated with capture‐mark‐recapture density estimates for snowshoe hares and were highly correlated with snow track transect density estimates for lynx and coyotes. Camera hit rates were not correlated with independent density estimates for red squirrels.
In this paper, we propose a novel framework for multi-target multi-camera tracking (MTMCT) of vehicles based on metadata-aided re-identification (MA-ReID) and the trajectory-based camera link model ...(TCLM). Given a video sequence and the corresponding frame-by-frame vehicle detections, we first address the isolated tracklets issue from single camera tracking (SCT) by the proposed traffic-aware single-camera tracking (TSCT). Then, after automatically constructing the TCLM, we solve MTMCT by the MA-ReID. The TCLM is generated from camera topological configuration to obtain the spatial and temporal information to improve the performance of MTMCT by reducing the candidate search of ReID. We also use the temporal attention model to create more discriminative embeddings of trajectories from each camera to achieve robust distance measures for vehicle ReID. Moreover, we train a metadata classifier for MTMCT to obtain the metadata feature, which is concatenated with the temporal attention based embeddings. Finally, the TCLM and hierarchical clustering are jointly applied for global ID assignment. The proposed method is evaluated on the CityFlow dataset, achieving IDF1 76.77%, which outperforms the state-of-the-art MTMCT methods.
Increased interest has been witnessed for full-field techniques measuring vibrations. 3D vision methods coupled to two high-speed cameras have proven to be a valid solution to measure 3D ...displacements, notably with the Stereo Digital Image Correlation (SDIC) tools. The now conventional pseudo-stereo system with a single high-speed camera and a four-mirror adapter, generating two virtual cameras, may also be used, even if it is rather complex to operate and remains limited to small objects. In a logic of simplification of the protocol, the authors present here a set-up requiring a single high-speed camera and no mirrors, with the associated full-field single-axis vision method. The latter is logically designed to measure the vibrations of items whose displacements are locally along a single axis (usually normal to the surface). This paper reports firstly the results of the full-field measurement of the vibrations of a plate, validated by a comparison with those obtained with the four-mirror adapter set-up, and secondly the application to the full-field measurement of the vibrations of a tambourine. Thirdly, the conventional pseudo-stereo technique and the proposed vision method are compared and assessed, in order to establish their respective limits and potential complementarity. Finally, once the application of the method to plane objects is validated, measurements have been carried out on a non-planar object: a bent plate; the results obtained highlight the possibility of using the proposed approach for non-planar surfaces.
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