Position And Orientation System Research Articles

Calibration and Compensation of the Scale Factor Errors in DTG POS

This paper proposes a calibration and compensation method of an inertial measurement unit (IMU) composed of two dynamically tuned gyros (DTGs) and three quartz accelerometers. Considering the DTG IMU for the position and orientation system (POS) used in the air remote sensing, it is found that the gyro scale factor has a hyperbolic relationship with the input angular rate and a linear relationship with the temperature shown from the experiments. Based on this, the equations of the gyro scale factor, the input angular velocity and the temperature are established by applying the least-square fit. Next, a hybrid multiposition calibration method of the IMU is given to estimate the error model parameters and compensate system errors. At last, a laboratory rate test and a car-mounted experiment are carried out to assess the efficiency of the proposed method. It is demonstrated from the experiment results that the attitude accuracy of the DTG POS can be improved with the calibration based on the compensation of scale factor errors.

THE PERFORMANCE ANALYSIS OF A UAV BASED MOBILE MAPPING SYSTEM PLATFORM

Abstract. To facilitate applications such as environment detection or disaster monitoring, the development of rapid low cost systems for collecting near real-time spatial information is very critical. Rapid spatial information collection has become an emerging trend for remote sensing and mapping applications. This study develops a Direct Georeferencing (DG) based fixed-wing Unmanned Aerial Vehicle (UAV) photogrammetric platform where an Inertial Navigation System (INS)/Global Positioning System (GPS) integrated Positioning and Orientation System (POS) system is implemented to provide the DG capability of the platform. The performance verification indicates that the proposed platform can capture aerial images successfully. A flight test is performed to verify the positioning accuracy in DG mode without using Ground Control Points (GCP). The preliminary results illustrate that horizontal DG positioning accuracies in the x and y axes are around 5 m with 300 m flight height. The positioning accuracy in the z axis is less than 10 m. Such accuracy is good for near real-time disaster relief. The DG ready function of proposed platform guarantees mapping and positioning capability even in GCP free environments, which is very important for rapid urgent response for disaster relief. Generally speaking, the data processing time for the DG module, including POS solution generalization, interpolation, Exterior Orientation Parameters (EOP) generation, and feature point measurements, is less than one hour.

Research on Motion Compensation for Airborne SAR Interferometry System

Deviation from definitive flight path of a plane fixed a synthetic aperture radar (SAR) leads to inaccurate and defocused radar images, which has serious effect on the SAR interferometry (InSAR) processing. Therefore, the precise motion compensation (MOCO) for the airborne SAR interferometric data is the key to obtain high quality digital elevation model (DEM).The position and orientation system (POS)-based residual motion error compensation method is designed. Considering the precision of POS, there will be residual motion error after the POS-based MOCO, which have serious effect on the interferometric phase, especially the residual baseline errors. To solve the above problem, this paper proposed an enhanced multi-squint processing based model to estimate the residual baseline errors. This method can decrease the influence of data decorrelation and baseline error varying with range, and dramatically improve the measuring accuracy of InSAR.

Kinetics and Design of a Mechanically Dithered Ring Laser Gyroscope Position and Orientation System

The motion compensation based on ring laser gyroscope (RLG) position and orientation system (POS) is a key technology to improve the imaging quality and efficiency of airborne Earth observation system. However, RLG POS faces great problems in the vibration environment, where the mechanical dither of RLG causes the adverse disturbance to inertial measurement unit (IMU) which should be eliminated, and the external vibration must be accurately measured with high bandwidth and low noise. To solve the problem, a kinetics model of RLG IMU is established based on a vibration response mechanism in this paper. An optimized design method of mechanically dithered RLG IMU with a vibration-damping system is proposed that can reduce the measurement error. In addition, the size-effect error and optimization method of RLG IMU are analyzed. Based on finite-element analysis software, a high-precision mechanically dithered RLG POS is designed and developed to be used in various imaging payloads. The experimental results show that the inertial navigation errors of RLG POS are 0.196 (σ), 0.659 (σ), and 0.707 kn (σ) for static, vehicle, and airborne experiments, respectively. It contributes to realize high-quality image of airborne interferential synthetic aperture radar and 1 : 500 scale map of camera without ground control marks. The precision of developed RLG POS is close to that of the most advanced production POS/AV610.

Improving the Error Model for POS Applicationto Airborne InSAR

Position and Orientation System (POS) is a technology widely used for motional error compensation of airborne InSAR. The measurement errors of inertial sensor (accelerometers and gyros) are the chief influencing factors to the precision of POS. In order to enhance the accuracy of POS, an improved SINS error model should be used in POS. In this paper, a more precise error model for SINS is developed by augmenting random walks error, first-order Markov process error, scale factor error and installation error. To validate the accuracy of the improved error model, semi physical flight simulation based on the imitation of imaging-flight route of InSAR is made to compare with the traditional SINS error model which only considering the random constant error. The simulation results show that the accuracy of the improved SINS error model is one order higher than the traditional SINS error model.

Compensating Impact of the Roll Variation of Airborne Platform on Laser Point Cloud from Airborne LiDAR

The roll variation of airborne platform has significant impact on the coverage area and point density of the laser point cloud obtained by airborne LiDAR. Thus, it is of practical significance to compensate the impact of roll variation. In this paper, a compensation device was designed firstly, including the mechanical structure and control system, to compensate the impact of roll variation on the laser point cloud. Then, the compensation principle of the airborne LiDAR with the designed compensation device was analyzed. Finally, the actual working procedure of the airborne LiDAR with the designed compensation device was simulated, in which the measurement errors of the position and orientation system (POS), as well as the measurement errors and control errors of the designed compensation device has been considered. The experimental results show that the designed compensation device is effective to compensate the impact of the roll variation.

Quaternion-Optimization-Based In-Flight Alignment Approach for Airborne POS

Position and Orientation System (POS) is a key technology that provides motion compensation information for imaging sensor in airborne remote sensing. In-flight alignment (IFA) is an important alignment method that can improve reaction speed and accuracy of measurement for airborne POS. The traditional IFA methods based on the Kalman filter and the adaptive extended Kalman filter (AEKF) are severely affected by flight maneuver; severe maneuver may result in alignment accuracy degeneration or failure. On the basis of optimization-based alignment method for static base alignment, a novel IFA method based on quaternion optimization is devised in this paper, aiming to boost up the robustness and the accuracy of IFA, which extends the range of the application of optimization-based alignment method from static base alignment to IFA. The proposed algorithm has the advantage that it can avoid the affection from severe maneuver. The real-time implementation is given. Flight experiment demonstrates that, compared with the IFA method based on AEKF, the proposed algorithm is better in converging speed and robusticity with the same alignment accuracy.

In-Flight Alignment Algorithm Based on ADD2 for Airborne POS

The Position and Orientation System (POS) is a special Strapdown Inertial Navigation System (SINS)/Global Positioning System (GPS) integrated system, widely employed in airborne remote sensing. In-Flight Alignment (IFA) is an effective way to improve the accuracy and speed of initial alignment for an airborne POS. IFA is normally accomplished with references from the position and velocity of GPS for SINS, so that unstable GPS measurements will result in poor alignment accuracy. To improve alignment accuracy under unstable GPS conditions, an adaptive filtering algorithm of the Second-order Divided Difference filter (DD2) based on adaptive innovation estimation is proposed, which introduces calculated innovation covariance directly into computation of the filter gain matrix. Then, the adaptive DD2 algorithm is used for the IFA of the POS with a large initial heading error. To validate the proposed algorithm, simulations are undertaken, followed by IFA experiments for the prototype of the airborne POS (TX-F30) under a turning manoeuvre in a car-mounted experiment, and under an “8” manoeuvre in-flight. The simulations and experimental results show that the proposed algorithm can reach better alignment accuracy under unknown statistical characteristic of GPS measurement noises.

POS System Boresight Misalignment Calibration with Bundle Adjustment Method

The boresight misalignment between inertial measurement unit(IMU) and sensor should be calibrated firstly for direct georeferencing(DG) of aerial photogrammetry.For this reason,the authors presented a simple and convenient boresight calibration model of position and orientation system(POS)-supported bundle block adjustment,and derived the fundamental error equation.The calibration result of this method is accordant with the calibration result of the commercial software CALQC in two empirical blocks.The method of boresight misalignment calibration proposed in this paper is correct and effective,as evidenced by a comparison with the DG results and y-parallax.The exterior orientations corrected with the calibration result can be directly used for mapping the topographic map at the scale of 1 ∶ 10 000 in high mountain areas.

NEW METHOD FOR THE CALIBRATION OF MULTI-CAMERA MOBILE MAPPING SYSTEMS

Abstract. Mobile Mapping Systems (MMS) allow for fast and cost-effective collection of geo-spatial information. Such systems integrate a set of imaging sensors and a position and orientation system (POS), which entails GPS and INS units. System calibration is a crucial process to ensure the attainment of the expected accuracy of such systems. It involves the calibration of the individual sensors as well as the calibration of the mounting parameters relating the system components. The mounting parameters of multi-camera MMS include two sets of relative orientation parameters (ROP): the lever arm offsets and the boresight angles relating the cameras and the IMU body frame and the ROP among the cameras (in the absence of GPS/INS data). In this paper, a novel single-step calibration method, which has the ability of estimating these two sets of ROP, is devised. Besides the ability to estimate the ROP among the cameras, the proposed method can use such parameters as prior information in the ISO procedure. The implemented procedure consists of an integrated sensor orientation (ISO) where the GPS/INS-derived position and orientation and the system mounting parameters are directly incorporated in the collinearity equations. The concept of modified collinearity equations has been used by few authors for single-camera systems. In this paper, a new modification to the collinearity equations for GPS/INS-assisted multicamera systems is introduced. Experimental results using a real dataset demonstrate the feasibility of the proposed method.

Strap‐down stabilization for multi‐load optoelectronic imaging platform

PurposeThe purpose of this paper is to describe a strap‐down image stable strategy for multi‐load optoelectronic imaging platform hung below a tethered aerostat.Design/methodology/approachFour two dimension pods, each with a visible light camera, are fixed on the optoelectronic platform. A POS (Position and Orientation System) is used to acquire the attitude rate data of optoelectronic platform, while the data can be coupled to the pods' servo systems through corresponding coordinate rotation, then the motors of pods will adjust the line of sight to the opposite way to keep the stabilization of image exported by visible light camcorders. Simultaneously, two rate gyros are installed at the inner frame of each pod, which are used as a backup to avoid the failure of POS.FindingsUsing one attitude and position measurement system can realize the stabilization of multi optoelectronic pods, which is same as or even better than the ratio gyro stabilization.Research limitations/implicationsAs the tethered aerostat is a flexible body, it is affected a lot by the wind speed and wind direction at the low height (<1,000 m), which leads to the motors of pods always adjust the line of sight to the mechanical limiting of pods.Practical implicationsStrap‐down stabilization technology has been successfully used in the tethered aerostat monitoring platform to surveillance Shanghai World EXPO site. Long time experiments verify the feasible and effective of the multi‐load stabilization technology. The impact on the image by the adjustment of servos is less than 10 percent of the whole view of sight.Originality/valueThe paper introduces a strap‐down stabilization technology for multi‐load tethered aerostat platform, which is more suitable to be applied in the platform of relatively minor attitude change, like the airborne multi‐load platform and multi‐load UAV (unmanned aerial vehicle) platform.

Boresight Calibration of Airborne LiDAR System Without Ground Control Points

This letter proposes a new method for boresight misalignment calibration of the charge-coupled device (CCD) camera which is one component of an airborne light detection and ranging (LiDAR) system without ground control points (GCPs). In the calibration, tie points in overlapping areas are first selected, and then, a multibaseline forward intersection is used for calculating object coordinates of these points. In the intersection, exterior elements of the CCD camera are obtained directly from positioning and orientation system (POS) data of the LiDAR system, which are error contaminated mainly due to the unparallel relation between the frameworks of the inertial measurement unit of the POS and the CCD camera. Elevation values of the ground points are then refined by those obtained from LiDAR point clouds by interpolation, which can be considered to be more accurate than those obtained by multibaseline forward intersection. Through projecting the ground points with refined elevation values into the image space by collinear equations and minimizing distances between the image points selected manually and those projected from ground points, the boresight misalignment is removed effectively. Therefore, the proposed method without GCPs in the whole process is more flexible than other traditional photogrammetric ways.

A Study of the Method of Automatic Extraction of Image Points for UAV Imagery with Large Overlap

A single control point may appear in multiple adjacent images because the unmanned aerial vehicle(UAV) images have high overlap degree.In the aerotriangulation work,the extraction of control points on images is a complex work.The original position and orientation system(POS) data can be corrected using the UAV images and control points,and then the corrected data can be applied to the work of points extraction.In this paper,an automatic extraction image points method suitable for large overlap images was put forward,and the accuracy of points extraction was assessed according to different terrain areas.Experimental results show that the method has higher precision in the flat terrain area and can be directly applied to the fast image mosaic,aerotriangulation and other follow-up processes.

DEM generation and error analysis using the first Chinese airborne dual-antenna interferometric SAR data

Terrain survey with traditional photogrammetry is often difficult in western China, such as Qingzang tableland at an average height of 5000 m above sea level and the southwest China area with cloudy weather. To resolve western terrain mapping, the first Chinese single-pass airborne Interferometric Synthetic Aperture Radar (InSAR) system was successfully developed by the Institute of Electronics, Chinese Academy of Sciences (IECAS) in 2004. The main objective of this article is to examine and evaluate the performance of the airborne SAR system through interferometric processing and error analysis. First, the article describes how high-precision digital elevation models (DEMs) are derived from the airborne dual-antenna (single-pass) InSAR data. In order to improve the precision, the antenna eccentricity correction and parameter calibration with the least square method (LSM) are proposed. Based on the airborne dual-antenna InSAR bore-sight model, this article summarizes the primary factors that influence the accuracy of DEMs in data processing, and analyses the errors induced by these factors. Then, the global positioning system (GPS)/inertial measurement unit (IMU) data, acquired and stored by the position and orientation system (POS), is used for analysing the quantitative relationships among the platform height, baseline length, baseline angle, look angle and DEM error. The experimental data used are airborne dual-antenna X-band InSAR data, and the measured ground control points (GCPs) are used to validate the accuracy of the DEM. The evaluation results in terms of the standard deviation (SD) and the average mean error (AME) are derived by comparing the reconstructed InSAR DEM with the reference GCPs. The AMEs of the X-direction, the Y-direction and the height are up to 2.078, 9.149 and 1.763 m, respectively. The SDs of the X-direction, the Y-direction and the height are up to ±1.379, ±0.764 and ±1.086 m, respectively. These results agree with the previously calculated quantitative errors. The error value of the Y-direction seems too large, a possible result of system errors. In general, the airborne dual-antenna InSAR system initially meets the requirements of 1:50 000 terrain mapping in western China.

Direct Sensor Orientation of a Land-Based Mobile Mapping System

A land-based mobile mapping system (MMS) is flexible and useful for the acquisition of road environment geospatial information. It integrates a set of imaging sensors and a position and orientation system (POS). The positioning quality of such systems is highly dependent on the accuracy of the utilized POS. This limitation is the major drawback due to the elevated cost associated with high-end GPS/INS units, particularly the inertial system. The potential accuracy of the direct sensor orientation depends on the architecture and quality of the GPS/INS integration process as well as the validity of the system calibration (i.e., calibration of the individual sensors as well as the system mounting parameters). In this paper, a novel single-step procedure using integrated sensor orientation with relative orientation constraint for the estimation of the mounting parameters is introduced. A comparative analysis between the proposed single-step and the traditional two-step procedure is carried out. Moreover, the estimated mounting parameters using the different methods are used in a direct geo-referencing procedure to evaluate their performance and the feasibility of the implemented system. Experimental results show that the proposed system using single-step system calibration method can achieve high 3D positioning accuracy.

An Approach to the ADS40 POS Data Processing Method Based on Precise Point Positioning

POS(Position and Orientation System) provides position and attitude information during aerial photography.There must be at least one reference GPS base station for traditional differential GPS(DGPS) positioning,and the establishment of a GPS station would be a very costly and difficult task in some areas.GPS Precise Point Positioning(PPP) has been advanced as a way to avoid the use of the GPS base station.This paper describes the approaches to the processing of an actual aerial photographic data by using both kinds of GPS positioning methods.The final results of the POS-supported aerial triangulation from PPP are compared with those from DGPS solution.The empirical results suggest that the accuracy of POS-supported aerial triangulation from PPP can satisfy the 1∶2 000 topographic map specifications for aerophotogrammetric office operation.It is feasible to process the POS data of ADS40 without a GPS Base Station by using Precise Point Positioning.

Transformation method of exterior orientation angular elements obtained via position and orientation system under Gauss-Kruger projection coordinate system

Data obtained via airborne position and orientation system (POS) is in WGS 84 global geocentric reference frame, while the national coordinate reference system for topographic mapping in China is generally Gauss-Kruger projection coordinate system. Therefore, data obtained via a POS must be transformed to national coordinate system. Owing to the effects of earth curvature and meridian deviation, there are some errors in the process of angle transformation from roll, pitch, and heading (Φ,Θ,Ψ) obtained directly via a POS to the attitude angles of images (φ,ω,κ) needed in photogrammetry. On the basis of effect theories of earth curvature and meridian deviation on exterior orientation angular elements of images, a method using a compensation matrix to correct the transformation errors from attitude angles obtained via the POS to exterior orientation angular elements of images is proposed in this paper. Moreover, the rigorous formula of the compensation matrix is deduced. Two sets of actual data obtained via a POS AV 510, which are different in scale and terrain, are selected and used to perform experiments. The empirical results not only indicate that the compensation matrix proposed in this paper is correct and practical but also show that transformation accuracy of exterior orientation angular elements obtained via the POS based on compensation matrix is relevant to the selection of vertical axis (a projection of central meridian) of Gauss-Kruger projection coordinate system; the proper vertical axis should be the Gauss-Kruger projection of the central meridian of projection zone in which the survey area locates. However, the transformation accuracy of exterior orientation angular elements is irrelevant to the choice of origin of coordinate system; it is appropriate that the origin of coordinate system locates at the center point of the survey area. Moreover, transformation accuracy of exterior orientation angular elements achieved based on the compensation matrix deduced in this paper is higher than that obtained via the existing POS processing software.

A novel method of systematic error compensation for a position and orientation system

A novel method is introduced for self-calibration and elimination of systematic errors for a position and orientation system (POS). The method uses a combined bundle block adjustment with POS data (named the POS-supported bundle block adjustment) without a calibration field. On the basis of delivering strict observation equations for POS data, the specific scheme of compensating the translation and drift systematic errors in a POS is given, and a prototype system WuCAPS is developed. The effects of eliminating POS systematic errors using the POS-supported bundle block adjustment for different ground control conditions are tested using two sets of actual aerial photos. The first set was taken over a flat region in the suburbs of the city of Yingkou in China and tested at a scale of 1:2500. The second set was taken over a high mountainous region in the desert region of Xinjiang in China and tested at a scale of 1:32,000. The empirical results verified that the POS systematic errors can be completely eliminated and the photo elements of exterior orientation obtained by the POS-supported bundle block adjustment can satisfy the requirements of aerial photogrammetric topographic mapping when four full ground control points (GCPs) are emplaced in the corners of the adjustment block for large-scale images of flat regions, but only one full GCP emplaced in the center of the adjustment block is needed for medium-small scale images of mountainous regions. This not only demonstrates the validity of the established mathematical model and the feasibility of the method proposed in this paper, but also avoids the use of a special calibration field. Therefore, it can simplify the existing POS operation rules and dramatically save on practical application costs, laying the theoretical foundation for widespread use of POS.

Some Investigations of Image Orientation in Aerial Photogrammetry

Aerial photogrammetry is the science and technology for obtaining three-dimensional spatial information about the Earth surface from aerial images.The key point of this issue is the rapid and accurate determination of image's position and attitude.This goal is met by aerial triangulation based on well distributed ground control points(GCPs) in conventional photogrammetry.With the wide application of global positioning system(GPS) and position and orientation system(POS),image exterior orientation elements can be acquired at the instant of imaging.Therefore,the stereo model reconstitution and direct georeferencing are becoming a new topic in aerial photogrammetry.Aerial triangulation evolves and progresses towards digital mapping without GCPs.This paper describes the operational issues and basic technical requirements of modern aerial photogrammetry.The accuracy of photogrammetric point determination and the y-parallax at corresponding model points are analyzed when stereo models are reconstituted by using the exterior orientation elements of aerial images.Real aerial photographs,at image scales from 1∶2 500 to 1∶60 000,with POS data taken over various topographic forms in China were processed by our POS-supported bundle block adjustment program WuCAPS.The empirical results verified that the accuracy of the exterior orientation elements from bundle block adjustment met the requirements of the specifications of topographic mapping.However,the accuracy of the exterior orientation elements determined by POS failed to meet the requirements of the specifications of topographic mapping.

A new coarse-to-fine rectification algorithm for airborne push-broom hyperspectral images

Rectification for airborne push-broom hyperspectral images is an indispensable and important task in registration procedure. In this paper, a coarse-to-fine rectification algorithm is proposed. In the coarse rectification process, the data provided by the Positioning and Orientation System (POS) is used in a model of direct georeference position to adjust the displacement of each line of images. In the fine rectification step, polynomial model is applied to realize that the geometric relationships of all the pixels in raw image space are same to those in the reference image. Experiments show that the fine rectified images are satisfying, and our rectification algorithm is very effective.