Please use the geomantic compass.

There are many kinds of geomantic compass discs, but basically there are three discs and three needles, namely, straight needle, sewing needle and middle needle. Positive needle: the northern position indicated by the floating needle in Tianchi, that is, the magnetic meridian, is used to define the context, also known as the territory. Sewing: the left half of the meridian of the Twenty-four Mountains, that is, the middle of the meridian of C, that is, the shadow noon seam, is used to correct the magnetic declination between straight needles, also known as the sky disk. Middle needle: the meridian of the North Pole, half a square to the left, that is, noon, also known as the human disk. "Exploring the Source of Feng Shui" said: "The establishment of the disk of heaven and earth is quite scientific and philosophical, which contains people's understanding and treatment of some psychological and physiological relationship between the geomagnetic declination and the human body, and is the practical application of China's philosophy of" heaven and earth are one "in architecture. However, with the knowledge of modern surveying and mapping, compared with the ancient geomantic compass, it is still too rough to divide the gold. In order to unify the positioning method of modern geological compass with the concept of three needles of geomantic compass and facilitate the conversion between them, modern surveying knowledge is introduced. Modern measurement knowledge: the true meridian: the plane passing through a point on the ground and the earth's rotation axis is the true meridian plane of that point. The direction in which the true meridian plane intersects the horizontal plane of the point is the true meridian direction of the point. The true meridian direction is determined by astronomical observation (see figure 4 1-35). Magnetic meridian: The direction of the compass needle when it is stationary (see Figure 4 1-35). Because the geomagnetic pole does not coincide with the earth's pole, the magnetic meridian direction at the same place is usually inconsistent with the true meridian direction, and the included angle between them is declination (see Figure 4 1-35). The magnetic needle is facing west. Generally speaking, it is negative in China. Underground power lines, iron substances, earthquakes, thunderstorms and other anomalies will change the magnetic declination. The magnetic declination varies slightly from place to place. Compass: A compass is an instrument for measuring the magnetic azimuth or magnetic quadrant angle of a straight line. The main components are magnetic needle, dial and calibration equipment. The aiming equipment refers to the aiming board (see figure 1-36). Followed by the magnetic needle and dial. Horizontal bubble. Their uses are: (1) aiming board: used to aim at the target, and with the magnetic needle, the magnetic orientation can be read; If the leveling bubble is matched, the principle of three points on a line can be used to measure the terrain slope or terrain height (see figures 1-37 and 1-38). (2) Magnetic needle: indicates the magnetic meridian direction. One end of the pointer is tied with a copper wire as a guide. Because China is located in the northern hemisphere, the magnetic field intensity of N pole is high, so the copper wire is stuck in S imitation for dry balance. (3) Dial: divided into 360. Read azimuth and quadrant angle as required. For example, the reading of the target object, the square angle is 3 15. Its quadrant angle is 45 degrees northwest. (4) Level bubble: Geological compass generally has two bubbles, one is round, which is used to make the compass level and the magnetic needle level, and the reading is accurate; The other is tubular, which is used to keep the horizontal position and read the elevation angle or inclination angle when measuring the height. The relationship between the above three aspects: ① the aiming direction of the aiming device and the O of the dial. Diameter lines are fixed together. The independent rotation of the magnetic needle points to the magnetic north-south direction, and the reading is read according to the southern or northern end of the magnetic needle. ② O of magnetic needle and dial. The diameter lines are fixed together, so that the o of the dial. The diameter always refers to the magnetic north-south direction, while the aiming device rotates to aim at the reading. Adjust it with the adjusting screw beside the compass (see figure 1-38). The magnetic declination can be based on the value marked on the local topographic map. When measuring, put the center of the compass on the plumb line at the starting point of the straight line, and aim at the measurement according to the above method. The standard directional lines used in measurement include true meridian, magnetic meridian and vertical coordinate axis in horizontal projection plane. For example, orient the house. The right center of the house can be marked with a rectangular coordinate line, and the intersection of the compass center and the rectangular coordinate line will coincide, depending on the angle between the compass and the ordinate (including after setting the level and aiming at the north pole). Then add or subtract the magnetic declination value, which is the correct direction value of the building, that is, the angle value between the true meridian and the ordinate. (This value can be converted by the position of the twenty-four mountains. Another example is the field work: (Illustrated by the topographic map with the scale of 1: 10000. ). l Find the distance between points A and B, and set points A and B. The measured figure is 1.7 cm, and the field distance is1:10000 =1.7, x, x 2170. 2. Find the elevation of points A and B. Since the contour distance is 0.5m, the position of A is just in the center of 4.5-5.o, so the elevation of position A is 4. ? 5 meters. The position of B is on the side of elevation 3.5 meters. Therefore, first, measure the vertical distance between two adjacent contour lines (the shortest distance between two contour lines in this figure is 0.8 cm of line AB), and let the lengths of B or B A be 0.5 cm, 0.3 cm and 0.5 m (50 cm) respectively. So the height formula of point B is 0.8: 50. So the elevation of point B is 3.69m (see Figure 4 1-39). 3. When the topographic map can't be consistent with the ground features, the height can be observed by benchmarking. For example, put a pole at two points AB and aim the compass at point A, so that the horizontal bubble in the compass is in the center and the line of sight is in the horizontal position. Measure the number of B' at the same time, then B'B is the relative height of point A (see Figure L-40). Table 1-7 Overview of main mountain ranges in China Note: Atlas of People's Republic of China (PRC).