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Azimuth positioning and horizontal angle positioning

1 introduction

ships sailing along the coast must regularly determine the ship's position by striking marks in front of the fluctuations in the vanadium market. There are many methods to determine the ship position, including azimuth positioning, distance positioning, horizontal angle positioning, line shifting positioning and comprehensive positioning. At present, ships often use radar landmarks for positioning, and its advantages are self-evident. It can not only locate the azimuth and distance of a single target, but also locate the azimuth and distance of two or three or even multiple targets. In addition, radar positioning is all-weather and is not limited by visibility conditions. However, once the radar fails, we should also learn to use other means to accurately determine the position of landmarks. For example, azimuth mirror positioning is a very effective means, and sextant horizontal angle positioning is also one of the effective positioning means. Because the accuracy of azimuth positioning is not only related to the level of the surveyor, but also directly related to the error of the compass. Therefore, the azimuth positioning error is often large; In addition, due to the long time of horizontal angle positioning and observation, chart operation is relatively difficult, so ships rarely use it. This paper wants to compare the advantages and disadvantages of azimuth positioning and horizontal included angle positioning, and combine them organically, so that the ship can get a more accurate position when it is relatively convenient under certain conditions

2 azimuth positioning 2. Is the equipment controlled by microcomputer (such as microcomputer controlled electronic universal experimental machine (floor type)? And horizontal angle positioning method

2.1 azimuth positioning method: use the compass to observe the azimuth of the object to obtain the compass azimuth of the object. After converting the true azimuth by compass difference, draw the azimuth position line on the chart, and the intersection of the position line is the positioning ship position. Specific method: add or subtract 180 degrees from the true shore position of the ship to the true shore position of the ship, and then draw the position line of the ship from the object mark. (as shown in Figure 1)

2.2 horizontal angle positioning method: observe the horizontal included angle formed by three or four objects at the same time, and you can get the arc ship position line. The intersection of the two ship position lines is the ship position at the observation time. Specific method: geometric drawing, set the horizontal included angle as α， Connect the two objects with a straight line and make 90 degrees at the object - α （ α When the computer sends the control signal to the servo valve> 90 degrees, draw the vertical bisector of the object line in the opposite direction at point O, and then draw an arc with o as the center and the distance from O to the object as the radius, that is, the position line of the ship. (as shown in Figure 2)

3 Analysis of azimuth positioning and horizontal included angle positioning

3.1 there are several reasons for the ship position error (two azimuth positioning) or the ship position error triangle (three azimuth positioning) caused by azimuth positioning:

(a) the observation error when observing the azimuth

(b) painting during chart operation → errors of standard strand, indented strand, compact strand, epoxy resin steel strand and PC strand

(c) error caused by not accurately observing at the same time

(d) error caused by inaccurate position of chart objects

(E) error caused by compass inaccuracy. Among them, the observation error should be basically the same for the same observer at the same time, which can be expressed by △ tb1; The error of chart operation can be reduced by improving the level of chart operation, including being careful; At the same observation time, we can't reduce the error by choosing the appropriate observation sequence, such as first the head and tail direction, and then the positive and horizontal direction; The inaccuracy of chart objects is difficult to overcome, but it should be relatively small; Compass error can be magnetic compass or electric compass. For example, errors caused by radar and antenna bow direction and horizontal beam width can be uniformly expressed by △ TB2. Therefore, the target straight orientation TB should include systematic errors and random errors such as TB measurement + △ tb1 + △ TB2. It is not difficult to analyze that △ tb1 and △ TB2 of the same ship, the same surveyor and different objects observed at the same time are almost equal, so the horizontal included angle of the two objects is: α= Tb1-tb2= (TB measurement 1+ △ tb1+ △ TB2) - (TB measurement 2+ △ tb1+ △ TB2) = TB measurement 1-tb measurement 2, which basically eliminates the errors caused by equipment and other reasons, and can be considered to be relatively accurate

3.2 the horizontal included angle positioning is the most accurate positioning method in the land mark positioning. The reason why it is accurate is that the horizontal included angle of the object observed by sextant itself is much higher than the compass observation angle accuracy, and it is not affected by the compass error. In order to ensure the positioning accuracy of the horizontal included angle, there are also requirements in the observation sequence, that is, measure the objects on the same side first, and then on the other side. In addition, the biggest disadvantage of horizontal included angle positioning is that the ship and the three objects cannot be in the same circle. If the four points are in the same circle, the ship position cannot be drawn

4 conclusion

based on the above analysis, we can draw the following conclusions:

(1) using azimuth positioning, there will be systematic errors and random errors in varying degrees due to the reasons described in (III). In order to ensure the precision and width of landmark azimuth positioning, it is best to use three azimuth positioning

(2) if the ship is not in the same circle with the four points of the three objects, the horizontal included angle between the two objects can be calculated, and the geometric drawing method of the horizontal included angle can be used to draw the ship position line. Although it is more complex, the most accurate ship position can be obtained

(3) if the four points are in the same circle, only the azimuth line can be drawn directly, and the ship position error triangle will usually occur, The method to deal with the ship position error triangle is to draw the ship position according to the systematic error (that is, add or subtract 2-4 degrees from the original azimuth line to get another ship position error triangle, and then connect the corresponding angles of the two triangles, and the intersection of their connecting lines is the systematic error ship position) and the random error (take the intersection of the anti centerline of the triangle). Then, Take the midpoint of the line between the systematic error ship position and the random error ship position as the most or ship position

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