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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 Determination1 Position DeterminationThe 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 a combination
2、 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 the absolute p
3、osition 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 position determinati
4、on. For the majority of this work, visual observation to the stars has been replaced by electromagnetic measurements to or from artificial earth satellites.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 aircraft navi
5、gation.1.1 Inertial PositioningA 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-dimensional survey system.
6、 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 unit contains a gy
7、ro-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 direction via a quanti
8、tizer 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 survey is restrict
9、ed 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 and evaluates the
10、 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 is complete the kno
11、wn 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 with respect to the
12、 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 the platform tangenti
13、al 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 vertical zero. As men
14、tioned 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 should read zero as sh
15、ould 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 after four minutes du
16、e 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 updating information and a zero velocity update is carried out; the Kalman filter carries out a smoothing adjustment data and results of the s
