1、 中文 6460 字 毕业设计（论 文） 外文资料原文与翻译 院 系： 专业班级： 学 号： 学生姓名： 指导老师： Automatic Position Determination 1 Position Determination The traditional method for the direct determination of position has been by astronomical observation. The relative positions and movements of the stars as well catalogued and so with
2、a combination of altitude, direction and time observations to the stars, the position in terms of latitude and longitude of a ground station can be calculated. There if less call for direct position determination nowadays since most countries are covered by a primary horizontal control scheme, and t
3、he absolute position of any new local survey word can be established by including a national reference point in the local survey. In very remote areas, or where the terrain is totally unsuitable for the classic survey methods of triangulation and traverse, there is, however, a need for direct positi
4、on determination. For the majority of this work, visual observation to the stars has been replaced by electromagnetic measurements to or from artificial earth satellites. In addition, the relative positions of survey stations can be determined directly by inertial techniques originally developed for
5、 aircraft navigation. 1.1 Inertial Positioning A pair of gyros are incorporated in a position fixing device known as the Auto-Surveyor manufactured by Litton Systems. It has originated from an aircraft navigation system, which was developed for military applications into its present three-dimensiona
6、l survey system. Hardware consists of (i)the inertial measuring unit, (ii)a computer ,(iii)a cassette recorder,(iv)a display and control unit and (v) the power supply .These items can be placed anywhere within a road vehicle or helicopter providing that the operator is close to (iv). The measuring u
7、nit contains a gyro-stabilized platform with two air-bearing gyroscopes in four gimbal mountings which keep its three orthogonal axis oriented in space in a north-east=downwards relationship . Each axis also has a sensor-torquer type of acclerometer which defines acceleration in the particular direc
8、tion via a quantitizer system feeding the computer .This is pre-programmed to compute the survey as it is carried out and to control the system (see Fig.1) Before staring the survey an alignment drill carried out at the origin station. This is said to have a duration of about one hour (that for the
9、survey is restricted to some four hours or so) and the platform levels itself with respect to the local vertical and aligns its nothing axis with the local meridian so that the accelerometers are in the directions of north, east and down. Simultaneously the computer monitors the biases of the system
10、 and evaluates the initial conditions for a Kalman filter enables an evaluation of the performance of the system by comparison of the errors arising during the survey to a priori data relating to the statistical nature of errors which navigation instruments are likely to contain. When the alignment
11、is complete the known coordinates and elevation of the station are fed in by the operator and the traverse can begin. The orthogonal movements are sensed by the accelerometers and, at intervals of sixteen milliseconds, the signals to the computer are doubly integrated into distances of displacement
12、with respect to the origin. In the Auto-Surveyor z-increments accumulate as elevation differences, whilst the other two increments are used to compute values of geodetic latitude and longitude on the pre-programmed reference spheroid. The computer also directs the platform gimbal torques to place th
13、e platform tangential to the spheroid with the north axis correctly oriented. At approximately four minute intervals the vehicle is halted a zero velocity updating is carried out. This takes about thirty seconds and the platform is re-leveled, with respect to local vertical, and effectively resets v
14、ertical zero. As mentioned above, previous calculations and platform torquing are with respect to the reference spheroid so that the amount of torque used for the re-leveling is a measure of the directional change of deviation from the vertical. Since the vehicle is stationary, the accelerometers sh
15、ould read zero as should the velocities by mtegration so that when the Kalman filter scrutinizes these values it can establish accelerometer errors due to their drift, which is non-linear, and it uses the velocity errors to establish the rate of change of drift； precise integration is not possible a
16、fter four minutes due to that drift. Platform re-leveling takes place after the adjustment. The survey now continues with successive updating stops and also with halts at the survey stations where the same process occurs. At the terminal station known coordinates and elevations are entered as updati
17、ng information and a zero velocity update is carried out； the Kalman filter carries out a smoothing adjustment data and results of the smoothing are registered on the recorder. Traverse lines are normally measured in two directions, occupying the same stations , discrepancies then indicating effects
18、 of gyrodrift on platform alignment .Standard errors of 0.20 m in position of points at 10 km separation are achievable with a similar value for heighting when a road vehicle is used. Ferranti manufacture a corresponding system in the UK, and reference can be made to a report in the New Civil Engine
19、er, 17 January 1980, on its value to the highway engineer. This report refers specifically to their Inertial Road Surveyor although it indicates that systems for land surveys, borehole surveys and underwater surveys are available too. 2 GPS IN NAVIGATIONAL APPLICATIONS 2.1 INTRODUCTION Global Positi
20、oning System (GPS) has for several years been a buzzword for professionals in many fields including surveying, geodesy, GIS, meteorology, and geodynamics. The reason for this GPS wonder perhaps lies in the superior capability of GPS: it offers solutions to many problems that we could not or felt dif
21、ficult to solve, and also enables us to do many things better than before. Navigation is one of these things, which has been greatly changed from the development of GPS. This paper will provide an overview of GPS as applied to navigation. It will first describe briefly the principles of GPS .The dif
22、ferent GPS based positioning methods in navigation will then be discussed, followed by an review of GPS based systems for air, land and marine navigation. 2.2 PRINCIPLES OF GPS POSITIONING GPS is a satellite based passive positioning system that was initially designed primarily for military use .It was developed and has been maintained by the United States Department of Defense (US DoD). The system is now used by both the military and civilian users to obtain high accuracy position, velocity and
