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Development of a Real-Time Electro-Optical Reconnaissance System
Published in David R. Martinez, Robert A. Bond, Vai M. Michael, High Performance Embedded Computing Handbook, 2018
As mentioned previously, our goal is to determine the geodetic coordinates of features in imagery, i.e., estimate the latitude, longitude, and altitude of the point of interest. Unlike radar, the products produced by a video sensor are inherently bearing-only—no range information is contained in the images. In addition, the ground points are not measured directly by the sensor, but indirectly through the amount of reflected light. The imaging plane of the camera captures the brightness of each point on the ground. If we assume the brightness of each is slowly varying over the time interval between frames, we can associate from frame to frame. Thus, as the aircraft flies over a scene, we can observe the motion of points through the frames, and the distance to each point from the sensor can be inferred based on the rate at which the points transit through the imagery: points closer to the camera will move through the field of view faster than will points that are farther away.
Geodesy Fundamentals
Published in Julio Sanchez, Maria P. Canton, William Perrizo, Space Image Processing, 2018
Julio Sanchez, Maria P. Canton
Latitude and longitude are the geographic or geodetic coordinates of a point on the earth’s surface. The latitude is expressed in degrees north or south of the equator, with a range of 0° to ±90°. The equator is the natural prime parallel. The longitude is usually measured east or west of the meridian that passes through the Greenwich Observatory in England. In this case, we say that the Greenwich meridian is the prime meridian. The range of longitudes is 0° to ±180°.
Comparison of advanced troposphere models for aiding reduction of PPP convergence time in Australia
Published in Journal of Spatial Science, 2019
In this section, we analyse the performance of each of the presented troposphere models by comparing the estimated ZTD from employing these models with the values obtained from the precise IGS ZTD product at selected stations in Australia. The stations analysed are distributed over the Australian continent and include Hobart (HOB2), Alice Springs (ALIC), Yarragadee (YAR2) and Townsville (TOW2). Table 1 shows the ITRF2008 geodetic coordinates (latitude, longitude and ellipsoid height) for these stations, extracted from the Asia Pacific Reference Frame (APREF) solution produced by Geoscience Australia for GPS week 1877. The Orthometric heights are also given, which were obtained from the Australian national geodetic database (www.ga.gov.au/ngrs). Since these stations are IGS reference stations, they have precise ZTD estimates available as an IGS product. These were used as reference values for comparison with results from the tested models. The analysis pertains to the full year from 1 January to 31 December 2016. The GRIB2 data was only available for approximately seven months of this period, due to connection issues that result in data outages.
A comparison of ship manoeuvrability models to approximate ship navigation trajectories
Published in Ships and Offshore Structures, 2023
Martin Alexandersson, Daiyong Zhang, Wengang Mao, Jonas W. Ringsberg
The experimental/full-scale test data in open water used for identifying the Abkowitz model often contains many noises and errors that must be processed/removed. Additionally, some input parameters may be missing or may not be measured precisely with ease. They must be estimated from other more ‘accurate’ parameters. In this study, the data collection frequency was 10 Hz. As shown in Figure 5, the surge and sway speeds show different trends of variation in comparison with normal manoeuvring test data, as in Figure 3. Furthermore, the speed of the experimental test model ship was only approximately 0.6 m/s, it thus became unsuitable to use the original formulas of rigid-body ship movement to estimate her speeds of u and v as input parameters for the Abkowitz model. Therefore, a new process for collecting data, pre-processing data, and estimating parameters for model identification is presented in Figure 7. First, biased data, such as significant discrepancies between the normal trajectories, (u, v, r, etc.) were deleted. Then, the missing data were added using a simple linear interpolation method. The Kalman filter was used to smooth the results from the ship trajectory. To establish the accurate manoeuvrability Abkowitz model using collected data from experimental tests at open water with large random noises, the input parameters as in Equation (6) that estimate the coefficients cannot be used as the initial speed U0 is uncertain. In this study, the parameters of u, v, and r were estimated using the geodetic coordinates in terms of observed instantaneous speed and course angle rather than a ship’s heading β: where Ui and ψi represent a ship’s instantaneous speed and sailing course at the i-th time step, and denotes the average ship speed. Finally, based on the parameters of u, v, and r using Equation (8) from the processed data, all the coefficients in the models were identified using the LS-SVM method.