Precision Of Navigation System Research Articles

Dataset and Benchmark: Novel Sensors for Autonomous Vehicle Perception

Conventional cameras employed in autonomous vehicle (AV) systems support many perception tasks but are challenged by low-light or high dynamic range scenes, adverse weather, and fast motion. Novel sensors, such as event and thermal cameras, offer capabilities with the potential to address these scenarios, but they remain to be fully exploited. This paper introduces the Novel Sensors for Autonomous Vehicle Perception (NSAVP) dataset to facilitate future research on this topic. The dataset was captured with a platform including stereo event, thermal, monochrome, and RGB cameras as well as a high precision navigation system providing ground truth poses. The data was collected by repeatedly driving two ∼8 km routes and includes varied lighting conditions and opposing viewpoint perspectives. We provide benchmarking experiments on the task of place recognition to demonstrate challenges and opportunities for novel sensors to enhance critical AV perception tasks. To our knowledge, the NSAVP dataset is the first to include stereo thermal cameras together with stereo event and monochrome cameras. The dataset and supporting software suite is available at https://umautobots.github.io/nsavp .

Navigation Techniques and Algorithms for Mobile Robots and Automated Guided Vehicles

Mobile robots are self-contained devices that can navigate and move around their surroundings. They observe their environment and create maps using different sensors such as lidar, Global Positioning System (GPS), and cameras. Automated Guided Vehicles (AGVs) are vehicles that can move independently utilizing different approaches such as underground cables, laser scanners, or GPS systems. This research investigates several navigation methodologies and algorithms used in AGVs and mobile robots. It focusses on the advantages of integrating lidar technology with other sensors as well as how it is used in local navigation techniques. We look at two motion planning techniques for obstacle avoidance: the Artificial Potential Field (APF) approach and the Vector Field Histogram (VFH) algorithm. Two effective techniques for finding the best routes are discussed: the A* algorithm and Dijkstra's algorithm. The various AGV types and their navigation systems (such as wired, guide, laser, vision-based, and gyro-based) are also examined in the study. Neural networks and fuzzy logic are investigated as AGV control techniques, with line following and obstacle avoidance as examples of their use. The study emphasizes how crucial precise and dependable navigation systems are to the effective and secure operation of mobile robots and AGVs.

Design and Development of Agri-bot for Autonomous Seed Sowing and Harvesting

Abstract: This research delves into the development of an Autonomous Agriculture Robot (AAR) capable of performing seed sowing and harvesting operations. The AAR operates in two distinct modes: seed sowing and harvesting, leveraging advanced sensors and a control system to automate these critical agricultural processes. The AAR is engineered with dual operational modes, facilitated by an encoder system for precise autonomous navigation, servo actuation for operational control, and a Battery Management System (BMS) for efficient power usage. This paper details the design and development of a hardware prototype that presents the integration of these technologies. Validation results demonstrate the AAR’s capability to autonomously navigate and perform the defined tasks. The implementation of the AAR prototype signifies a pivotal step towards automating manual agricultural processes, potentially transforming the agricultural landscape by reducing labour requirements and increasing efficiency.

Performance Evaluation of DGNSS Receiver for Dynamic Military Applications

In military applications, a highly accurate and precise navigation system is necessary for some ground-based combat system applications to navigate the vehicle and mark the location of the fuses and pickets laid by the mobile equipment. Few companies across the globe have developed expertise in manufacturing Global Navigation Satellite System (GNSS) receivers with Real Time Kinematics (RTK) capability along with integrated INS. On mobile equipment, it is not always possible to precisely place the Differential GNSS (DGNSS) antenna and GNSS receiver at the point for which the data needs to be marked. For such applications, lever arm calculation needs to be implemented. Also, due to uneven terrain conditions and slopes, the vehicle undulates up to 10o about its longitudinal and transverse axis. This dynamic condition induces considerable errors in the actual data. During the fuse laying process, there is also a continuous requirement for real-time location data in the GNSS-denied environment for a short period. INS was integrated with the GNSS receiver. We discuss test methodology for GNSS receiver performance evaluation. Experimentations were performed, taking into consideration these requirements. Data collected are also analyzed and discussed. Test results confirmed that the module is accurate with an accuracy of a few centimeters.

Developments of a centimeter-level precise muometric wireless navigation system (MuWNS-V) and its first demonstration using directional information from tracking detectors

Various positioning techniques such as Wi-Fi positioning system have been proposed to use in situations where satellite navigation is unavailable. One such system, the muometric positioning system (muPS), was invented for navigation which operates in locations where even radio waves cannot reach such as underwater or underground. muPS takes advantage of a key feature of its probe, cosmic-ray muons, which travel straightforwardly at almost a speed of light in vacuum regardless of the matter they traverse. Similar to other positioning techniques, muPS is a technique to determine the position of a client’s muPS receiver within the coordinate defined by reference detectors. This can be achieved either by using time-of-flight (ToF) or angle of arrival (AoA) measurements. The latter configuration (AoA), called the Vector-muPS has recently been invented and the present paper describes the developments of the first prototype of a vector muometric wireless navigation system (MuWNS-V) with this new vector-muPS concept and its demonstration. With MuWNS-V, the reference tracker and the receiver ran wirelessly with fully independent readout systems, and a positioning accuracy of 3.9 cm (RMS) has been achieved. We also evaluated the outcome of measuring continuous indoor localization of a moving receiver with this prototype. Our results indicated that further improvements in positioning accuracy will be attainable by acquiring higher angular resolution of the reference trackers. It is anticipated that “sub-cm level” navigation will be possible for muPS which could be applied to many situations such as future autonomous mobile robot operations.

Fast 50 Hz Updated Static Infrared Positioning System Based on Triangulation Method.

One of the important issues being explored in Industry 4.0 is collaborative mobile robots. This collaboration requires precise navigation systems, especially indoor navigation systems where GNSS (Global Navigation Satellite System) cannot be used. To enable the precise localization of robots, different variations of navigation systems are being developed, mainly based on trilateration and triangulation methods. Triangulation systems are distinguished by the fact that they allow for the precise determination of an object's orientation, which is important for mobile robots. An important feature of positioning systems is the frequency of position updates based on measurements. For most systems, it is 10-20 Hz. In our work, we propose a high-speed 50 Hz positioning system based on the triangulation method with infrared transmitters and receivers. In addition, our system is completely static, i.e., it has no moving/rotating measurement sensors, which makes it more resistant to disturbances (caused by vibrations, wear and tear of components, etc.). In this paper, we describe the principle of the system as well as its design. Finally, we present tests of the built system, which show a beacon bearing accuracy of Δφ = 0.51°, which corresponds to a positioning accuracy of ΔR = 6.55 cm, with a position update frequency of fupdate = 50 Hz.

Sistem Navigasi Robot Quadruped 12 DoF dengan Algoritma Dynamic Programing

The quadruped robot that has 4 legs as a means of locomotion can move from the previous place because it has a degree of freedom (DOF) on each leg. Of the 3 DOFs, each leg requires an algorithm to be able to create a precise navigation system. This is done because quadruped robots are more difficult to find balance in maneuvering. After all, this robot only has 3 fulcrum points in each movement on one leg of the robot. Giving the right algorithm to each leg of the robot will create a fit of movement where 3 legs will always be the pedestal when 1 leg of the robot is being lifted to ensure the robot does not collapse. Supported by the right algorithm, it will produce a good navigation system for the robot. In this study, the servo used was the Hitec HS-645MG servo type. To support testing on the navigation system in this study is to use ultrasonic sensors as distance reading input sensors in supporting robots in the navigation process. So that the robot can be controlled according to the input of the ultrasonic sensor that is inputted so that the robot does not touch the obstacles around it. (Abstract)

Optimization of high-power short duration catheter radiofrequency ablation for pulmonary veins isolation in patients with artiral septial defect

Objective ‒ to perform the analysis and biophysical substantiation of a new technique of catheter radiofrequency ablation (RFA) with high power and short duration based on mathematical modeling of own clinical data of the electro-thermodynamic effect of RFA on the myocardium; to investigate the morphological characteristics of the myocardium in different areas of the atrium and to determine the morphometric parameters of the display on the electroanatomical model of the heart of the ablation zone in the EnSite Precision navigation system, necessary for effective and safe high-power and short-duration RFA.Materials and methods. Clinical studies were performed in Amosov National Institute of Cardiovascular Surgery NAMS of Ukraine. Specialized high-tech medical equipment was used for the objectivity of clinical data obtained and used in the work. Morphological characteristics of the myocardium (thickness of the wall of the left atrium, distance from the back wall of the heart to the esophagus, diameters of the pulmonary veins) were evaluated on the computed tomography images of the heart of the patients, which were obtained in the radiology department on a Toshiba device (Japan) using a spiral scanning. The morphometric parameters of the ablation zone, which were later used to evaluate the effectiveness of RFA and which formed the basis of standardized protocols for the operation, were determined for display on the electro-anatomical maps of the patients' hearts in the EnSite Precision system (Abbott, USA). Biophysical substantiation of the RFA technique with high power and short duration was performed using mathematical modeling of the electro-thermodynamic effect of RFA on the myocardium and own clinical data in the Comsol Multiphysics automated simulation of biophysical processes.Results. It is proposed for a group of patients with combined atrial fibrillation with an atrial septal defect to perform RFA using a new ablation technique with high power and short duration at one point of application of radio frequency energy. Achieving transmurality of ablation in a shorter time makes it possible to hold the electrode more precisely and stably in this area when isolating the pulmonary veins in a complex geometry and without support for the electrode in case of a defect. The morphological characteristics of the myocardium were studied and the morphometric parameters of the display on the electroanatomical heart model of the ablation zone, necessary for effective and safe RFA, were determined. These include: the diameter of the point-label of radiofrequency ablation on the anatomical model of the heart, which must correspond to the real data of the size of the destruction; the percentage of overlap of RFA points for the formation of an effective transmural line; estimated number of ablation points to standardize the evaluation of the effectiveness of the procedure.Conclusions. The conducted research made it possible to solve the current problems of catheter radiofrequency ablation in patients with atrial fibrillation and atrial septal defect, namely to increase the efficiency and safety of pulmonary vein isolation. Transmurality and integrity of the isolating line was achieved due to the determined morphological characteristics of the myocardium and the calculated morphometric parameters of the ablation zone. The obtained data are adapted to a real display visible to the surgeon on the electro-anatomical map of the heart in the EnSite Precision navigation system. This system is actively used in clinical practice, but it was necessary to optimize the clinical protocols of RFA with high power and short duration, which was achieved as a result of this work.

The VISION – Concept of laser crosslink systems using nanosatellites in formation flying

Spaceborne data can be seamlessly handled using a laser-communication system that enables super-high-speed data transfers, greater than or equal to 1 Gbps, and provides size, weight, and power (SWaP) efficiencies at low costs. Laser-communication systems have garnered attention owing to their ability to enhance SWaP efficiencies, and thus they may complement or potentially replace traditional radio frequency (RF) systems in future space networks. Here, we propose a novel space-to-space laser communication system, called very-high-speed inter-satellite link system using infrared optical terminal and nanosatellite (VISION). This study aims to establish and validate laser-crosslink systems and advanced space technologies using two 6U nanosatellites in formation flying. The payload is a laser-communication terminal (LCT) containing a deployable space telescope. The LCT shares beam paths for communication as well as pointing, acquisition, and tracking (PAT) with a single aperture, thereby providing feedback control for the PAT and help mitigate steady-state beam pointing errors. The nanosatellites include a precise formation-flying guidance, navigation, and control system with an S-band RF crosslink and propulsion system. Each nanosatellite is equipped with a propulsion system that can change its inter-satellite ranges rapidly and accurately based on the mission operation scenarios. LCT payload prototypes are constructed, and the PAT system is evaluated using a testbed. Additionally, the components of the nanosatellite bus are electrically integrated for flatsat testing. The proposed laser-crosslink systems are anticipated to contribute to the establishment of high-speed and secure space-to-space networks at low costs in the forthcoming years.

Performance Analysis of Real-Time GPS/Galileo Precise Point Positioning Integrated with Inertial Navigation System

The integration of global navigation satellite system (GNSS) precise point positioning (PPP) and inertial navigation system (INS) is widely used in navigation for its robustness and resilience, especially in case of GNSS signal blockage. With GNSS modernization, a variety of PPP models have been developed and studied, which has also led to various PPP/INS integration methods. In this study, we investigated the performance of a real-time GPS/Galileo zero-difference ionosphere-free (IF) PPP/INS integration with the application of uncombined bias products. This uncombined bias correction was independent of PPP modeling on the user side and also enabled carrier phase ambiguity resolution (AR). CNES (Centre National d'Etudes Spatiales) real-time orbit, clock, and uncombined bias products were used. Six positioning modes were evaluated, including PPP, PPP/INS loosely coupled integration (LCI), PPP/INS tightly coupled integration (TCI), and three of these with uncombined bias correction through a train positioning test in an open sky environment and two van positioning tests at a complex road and city center. All of the tests used a tactical-grade inertial measurement unit (IMU). In the train test, we found that ambiguity-float PPP had almost identical performance with LCI and TCI, which reached an accuracy of 8.5, 5.7, and 4.9 cm in the north (N), east (E) and up (U) direction, respectively. After AR, significant improvements on the east error component were achieved, which were 47%, 40%, and 38% for PPP-AR, PPP-AR/INS LCI, and PPP-AR/INS TCI, respectively. In the van tests, frequent signal interruptions due to bridges, vegetation, and city canyons make the IF AR difficult. TCI achieved the highest accuracies, which were 32, 29, and 41 cm for the N/E/U component, respectively, and also effectively eliminated the solution re-convergence in PPP.

Visible CCD Camera-Guided Photoacoustic Imaging System for Precise Navigation during Functional Rat Brain Imaging

In photoacoustic (PA) imaging, tissue absorbs specific wavelengths of light. The absorbed energy results in thermal expansion that generates ultrasound waves that are reconstructed into images. Existing commercial PA imaging systems for preclinical brain imaging are limited by imprecise positioning capabilities and inflexible user interfaces. We introduce a new visible charge-coupled device (CCD) camera-guided photoacoustic imaging (ViCPAI) system that integrates an ultrasound (US) transducer and a data acquisition platform with a CCD camera for positioning. The CCD camera accurately positions the US probe at the measurement location. The programmable MATLAB-based platform has an intuitive user interface. In vitro carbon fiber and in vivo animal experiments were performed to investigate the precise positioning and imaging capabilities of the ViCPAI system. We demonstrated real-time capturing of bilateral cerebral hemodynamic changes during (1) forelimb electrical stimulation under normal conditions, (2) forelimb stimulation after right brain focal photothrombotic ischemia (PTI) stroke, and (3) progression of KCl-induced cortical spreading depression (CSD). The ViCPAI system accurately located target areas and achieved reproducible positioning, which is crucial in animal and clinical experiments. In animal experiments, the ViCPAI system was used to investigate bilateral cerebral cortex responses to left forelimb electrical stimulation before and after stroke, showing that the CBV and SO2 in the right primary somatosensory cortex of the forelimb (S1FL) region were significantly changed by left forelimb electrical stimulation before stroke. No CBV or SO2 changes were observed in the bilateral cortex in the S1FL area in response to left forelimb electrical stimulation after stroke. While monitoring CSD progression, the ViCPAI system accurately locates the S1FL area and returns to the same position after the probe moves, demonstrating reproducible positioning and reducing positioning errors. The ViCPAI system utilizes the real-time precise positioning capability of CCD cameras to overcome various challenges in preclinical and clinical studies.

Adaptive Multi-ROI Agricultural Robot Navigation Line Extraction Based on Image Semantic Segmentation.

Automated robots are an important part of realizing sustainable food production in smart agriculture. Agricultural robots require a powerful and precise navigation system to be able to perform tasks in the field. Aiming at the problems of complex image background, as well as weed and light interference factors of the visual navigation system in field and greenhouse environments, a Faster-U-net model that retains the advantages of the U-net model feature jump connection is proposed. Based on the U-net model, pruning and optimization were carried out to predict crop ridges. Firstly, a corn dataset was trained to obtain the weight of the corn dataset. Then, the training weight of the obtained corn dataset was used as the pretraining weight for the cucumber, wheat, and tomato datasets, respectively. The three datasets were trained separately. Finally, the navigation line between ridges and the yaw angle of the robot were generated by B-spline curve fitting. The experimental results showed that the parameters of the improved path segmentation model were reduced by 65.86%, and the mPA was 97.39%. The recognition accuracy MIoU of the Faster-U-net model for maize, tomatoes, cucumbers, and wheat was 93.86%, 94.01%, 93.14%, and 89.10%, respectively. The processing speed of the single-core CPU was 22.32 fps/s. The proposed method had strong robustness in predicting rows of different crops. The average angle difference of the navigation line under a ridge environment such as that for corn, tomatoes, cucumbers, or wheat was 0.624°, 0.556°, 0.526°, and 0.999°, respectively. This research can provide technical support and reference for the research and development of intelligent agricultural robot navigation equipment in the field.

Multi-GNSS PPP/INS/Vision/LiDAR tightly integrated system for precise navigation in urban environments

Nowadays, high-precision navigation is a fundamental prerequisite for autonomous driving technology. However, it is often difficult for a stand-alone sensor to meet the needs of high-precision navigation in complex scenarios. To address this problem, we propose a tightly coupled precise point positioning (PPP)/inertial navigation system (INS)/Vision/LiDAR integration method to achieve high-precision, continuous and reliable navigation in urban environments. The multi-GNSS carrier phase and pseudorange measurements, low-cost microelectromechanical system (MEMS) inertial measurement units (IMU) records, sparse visual landmarks and extracted LiDAR edge/planar features are directly fused at the observation level through a centralized Extended Kalman Filter (EKF). The vehicle experiments in different GNSS availability conditions were conducted to evaluate the proposed method. Results indicate that our proposed PPP/INS/Vision/LiDAR integration can maintain sub-meter level positioning in both GNSS half-open-sky and difficult environments, with improvements of (50.7%, 58.6%, 54.3%) and (46.2%, 55.0%, 58.8%) relative to PPP/INS/Vision and PPP/INS/LiDAR, respectively. Moreover, both visual and LiDAR information can significantly improve the velocity and attitude estimation performance, especially for the heading.

Evaluation of Seasonal Variability of First-Order Ionospheric Delay Correction at L5 and S1 Frequencies Using Dual-Frequency NavIC System

For the precise positioning applications it is important to determine and eliminate the positioning error introduced by various sources such as the ionosphere. To develop a standalone precise navigation system, India has launched the seven satellite constellations for NavIC (Navigation with Indian Constellation) system which can provide precision positioning over India and surrounded landmass. Since the ionospheric delay depends on the frequency of the satellite signal and NavIC systems work at different frequencies L5 and S1 than Global Positioning System (GPS) at L1 and L2, it is not possible to use the GPS data-driven study for NavIC based location calculations directly. Thus there is a need for a specialized ionospheric study for NavIC systems. In addition, the ionospheric delay is directly proportional to Slant Total Electron Content (STEC) which is dependent upon diurnal and seasonal solar activity. To achieve accurate positioning facilities, there is also a need for evaluation for seasonal variability of ionospheric delay correction for NavIC receivers. This paper deals with the STEC estimation; it's smoothing, and removal of instrumental biases from STEC. The determined true STEC has been used to determine first-order ionospheric delay correction at L5 and S1 frequencies. The delay correction at S1 has been found less (2–7 m) as compared to L5 (10–30 m). Furthermore, the seasonal variability of ionospheric delay has been analyzed using about 19 months of data (from June 2017 to December 2018) and found that the ionospheric delay follows unique seasonal characteristics which can be utilized for delay modeling. It has been also observed that the geostationary satellites of the NavIC system are more appropriate than geosynchronous satellites for ionospheric related studies.

Clock and Power-Induced Bias Correction for UWB Time-of-Flight Measurements

Ultra-Wide Band (UWB) communication systems can be used to design low cost, power efficient and precise navigation systems for mobile robots, by measuring the Time of Flight (ToF) of messages traveling between on-board UWB transceivers to infer their locations. Theoretically, decimeter level positioning accuracy or better should be achievable, at least in benign propagation environments where Line-of-Sight (LoS) between the transceivers can be maintained. Yet, in practice, even in such favorable conditions, one often observes significant systematic errors (bias) in the ToF measurements, depending for example on the hardware configuration and relative poses between robots. This letter proposes a ToF error model that includes a standard transceiver clock offset term and an additional term that varies with the received signal power (RxP). We show experimentally that, after fine correction of the clock offset term using clock skew measurements available on modern UWB hardware, much of the remaining pose dependent error in LoS measurements can be captured by the (appropriately defined) RxP-dependent term. This leads us to propose a simple bias compensation scheme that only requires on-board measurements (clock skew and RxP) to remove most of the observed bias in LoS ToF measurements and reliably achieve cm-level ranging accuracy. Because the calibrated ToF bias model does not depend on any extrinsic information such as receiver distances or poses, it can be applied before any additional error correction scheme that requires more information about the robots and their environment.

Analysis of an Unmanned Underwater Vehicle Propulsion Model for Motion Control

The knowledge of dynamic models to describe the behaviors of unmanned underwater vehicles allows to design a precise navigation, guidance, and control system. A practical identification strategy is presented in this contribution, a procedure that can be easily executed during field trials and that is able to obtain a rapid assessment about the characteristics of the vehicle dynamic model. The developed procedure is designed for small-size-class remotely operated vehicles, characterized by low operative speeds. The vehicle is equipped with proprioceptive sensors in charge of measuring data needed to identify its dynamic model. Building on the proposed practical identification experiments, different vehicle propulsion models are considered and analyzed: the first is a general theoretical model accounting for the vehicle hydrodynamics (standard marine Fossen model); the others are modified models introducing additional terms in the produced thrust (torque), namely, a term proportional to the rate of change of the propeller revolutions per minute (r.p.m.), (where is the revolution rate of the propeller), and a delayed copy of the terms connected to the fluid axial flow velocity. For all considered degrees of freedom, the fitting performance of the proposed models resulted to be superior to the first. Moreover, a control system building on the obtained dynamic characterization is described.

A robust H∞-based steering assistance system for the wheeled tractor.

Agricultural machine automatic navigation poses great challenge to the precise agricultural technology system nowadays. To this end, this paper proposes a novel steering assistance system (SAS) to assist drivers in the path-tracking. First, the driver steering model is investigated through the driver simulator tests. Combining the wheeled tractor kinematics model, a driver-vehicle model is developed. Then, a polytopic linear parameter-varying (LPV) system is adopted to describe the uncertainties, including time-varying driver model parameters and velocity, in the model, based on which an output-feedback robust controller is developed to ensure robust stability within the polytope space. Moreover, a regional pole placement method is adopted to improve the transient performance of the system. Finally, driver-in-the-loop and field tests conducted to value the controller. The results show the effectiveness of the proposed method to improve the path-tracking performance for the agricultural machine navigation, while reducing the physical and mental workload of drivers. This control method is expected to be a paradigm for the precise navigation system of the agricultural machinery.

Effect of Microstructure on the Dimensional Stability of Extruded Pure Aluminum.

High-performance extruded aluminum alloys with complex textures suffer significant dimension variation under environmental temperature fluctuations, dramatically decreasing the precision of navigation systems. This research mainly focuses on the effect of the texture of extruded pure aluminum on its dimensional stability after various annealing processes. The result reveals that a significant increment in the area fraction of recrystallized grains with <100> orientation and a decrement in the area fraction of grains with <111> orientation were found with increasing annealing temperature. Moreover, with the annealing temperature increasing from 150 °C to 400 °C, the residual plastic strain after twelve thermal cycles with a temperature range of 120 °C was changed from −1.6 × 10−5 to −4.5 × 10−5. The large amount of equiaxed grains with <100> orientation was formed in the microstructure of the extruded pure aluminum and the average grain size was decreased during thermal cycling. The area fraction of grain with <100> crystallographic orientation of the sample annealed at 400 °C after thermal cycling was 30.9% higher than annealed at 350 °C (23.7%) or at 150 °C (18.7%). It is attributed to the increase in the proportion of recrystallization grains with <100> direction as the annealing temperature increases, provided more nucleation sites for the formation of fine equiaxed grains with <100> orientation. The main orientation of the texture was rotated from parallel to <111> to parallel to <100> after thermal cycling. The change in the orientation of grains contributed to a change in interplanar spacing, which explains the change in the dimension along the extrusion direction during thermal cycling.

The Realization and Evaluation of PPP Ambiguity Resolution with INS Aiding in Marine Survey

The tightly coupled global navigation satellite system (GNSS) precise point positioning (PPP) and inertial navigation system (INS) can provide high-precision position, velocity and attitude information. The coupled system utilizes single receiver, which is particularly suitable for the environment without reference station, such as marine survey. In the former works, the integer ambiguity resolution of PPP/INS in terrestrial environment is researched. However, the GNSS observation is severely affected by the multipath effect in marine environment. In addition, the sideslip caused by wind and sea wave also impact float ambiguity estimation, consequently introducing difficulty for PPP ambiguity fixing. Therefore, the PPP/INS tightly coupled model with fixed ambiguity is proposed for marine survey. The correction model of INS gyroscope bias in closed-loop is deduced in detail. The influence of ship motion noise and multipath in marine environment is reduced by introducing the robust factor to the Kalman filter. The feasibility of the method is verified in a real marine experiment, with a detail evaluation of the data quality and positioning accuracy. The results show that the accuracy of PPP/INS can reach centimeter level after fixing the ambiguity in marine environment. Furthermore, the precise INS-predicted position can significantly shorten the re-fixed time of PPP/INS, which proves the efficiency of the proposed approach.

Method for 3-D Scene Reconstruction Using Fused LiDAR and Imagery From a Texel Camera

Reconstructing a 3-D scene from aerial sensor data creating a textured digital surface model (TDSM), consisting of a LiDAR point cloud and an overlaid image, is valuable in many applications including agriculture, military, surveying, and natural disaster response. When collecting LiDAR from an aircraft, the navigation system accuracy must exceed the LiDAR accuracy to properly reference returns in 3-D space. Precision navigation systems can be expensive and often require full-scale aircraft to house such systems. Synchronizing the LiDAR sensor and a camera, using a texel camera calibration, provides additional information that reduces the need for precision navigation equipment. This paper describes a bundle adjustment technique for aerial texel images that allows for relatively low-accuracy navigation systems to be used with low-cost LiDAR and camera data to form higher fidelity terrain models. The bundle adjustment objective function utilizes matching image points, measured LiDAR distances, and the texel camera calibration and does not require overlapping LiDAR scans or ground control points. The utility of this method is proven using a simulated texel camera and unmanned aerial system (UAS) flight data created from aerial photographs and elevation data. A small UAS is chosen as the target vehicle due to its relatively inexpensive hardware and operating costs, illustrating the power of this method in accurately referencing the LiDAR and camera data. In the 3-D reconstruction, the 1- $\sigma $ accuracy between LiDAR measurements across the scene is on the order of the digital camera pixel size.