Trigonometric leveling

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Basic Principles on the Calculation Method Edit this paragraph the basic principles of the basic principles of trigonometric leveling Figure, A, B two points on the ground,Adidas F50 TF, observing from point A to point B, the vertical angle α1.2 , S0 is the horizontal distance between two points, i1 point A instrument height, i2 spy for the elevation of point B, then A, B height difference between two points h1.2 = S0tga1.2 + i1-i2 above formula assumes that the Earth's surface is a plane, a straight line of sight conditions of observation derived. In geodesy, due to the side length is longer, you must take into account the curvature of the Earth and atmospheric vertical refraction differential impact. In order to improve the accuracy of trigonometric leveling, usually taken to the observation vertical angle, height difference between two points Deriving to weaken the impact of vertical atmospheric refraction.

 

edit this section affect one hundred years ago, trigonometric leveling is the main method of measuring height. Since the emergence of standard measurement methods, it has been relegated to secondary status. However, because the job is simple,Nike Flex Experience Rn Mens, in the mountainous and hilly areas are still widely used. Zenith distance observations being seriously affected by atmospheric refraction ground. If the atmospheric density is uniform, the light emitted by the light source L will be in the form of concentric spherical wavefront propagation in all directions, the speed and density of the atmosphere to adapt. In fact, the atmospheric density generally increases with the increase of height reduced, the upward velocity of propagation of light in the horizontal direction than the large. This is no longer concentric spherical wavefront, but in the form shown in Figure 1. At this station the observation light source S L, the telescope perpendicular to the wavefront, as seen by the direction of the light source, as shown by the arrows; dotted line in the figure the path of the line of sight, it is everywhere perpendicular to the wave front. This phenomenon is called the ground atmospheric refraction, depending on the direction of the light source and the true direction of the angle between the γ SL is called refraction angle. In trigonometric leveling, angle depends on the refractive index between the target station and observed the physical conditions of the atmosphere, especially the atmospheric density lapse rate upward. Surveying in practice, it is impossible to fully grasp the physical conditions of the atmosphere to calculate the refraction angle, there is generally only estimate its value, or take appropriate measures to weaken it to the final results. Edit this paragraph calculation method triangulation measurements to calculate the height difference between two points, is based on the ellipsoid,Adidas AdiPure FG, so obtained is ellipsoidal height elevation. Figure 2, A, B points of the ellipsoid height H1, respectively, and H2. First, excluding the vertical deflection omitted, set from point A to point B observed zenith distance of Z1 (or elevation angle α1 = 90 °-Z1), the two o'clock in the projection of ellipsoid arc length apart A0 and B0 as S0, A0B0 arc radius of curvature R0, then A and B height is: where is the earth curvature term impact; term effects of atmospheric refraction; k is the refraction coefficient, usually using the average k = 0.10 ~ 0.16 . The above is from point A to point B observed zenith distance Z1 (or height angle α 1), to find definite height difference between the two situations is called unidirectional trigonometric leveling. If A, B two points each observation zenith distance Z1 and Z2 (or height angle α 1 and α 2), set the required height difference between two points is called on to trigonometric leveling. Used for observation due to trigonometric leveling is carried out under the same conditions, two opposite directions refraction coefficient k can be considered approximately the same, and therefore do not have to consider the refraction correction items. Especially at the same time to be right when observed ellipsoidal height h of the equation simplifies to:. On the trigonometric leveling, assume the opposite direction of the refraction coefficient of the same, of course, may not be entirely realistic, but more than one way to apply trigonometric leveling much more reliable valuation of k. Therefore, generally used for the trigonometric leveling. Elevation above formula, not taking into account the vertical deviation of the station zenith distance to the observer effect. In flat areas used for the trigonometric leveling, this effect is small. In addition, the formula is derived from a process point of view, the determined height is ellipsoidal height, to be counted as being of high or normal system height, must join corrected. In the triangular mesh or wire network, can be determined by the trigonometric leveling ellipsoid height difference between two points, if more of these points obtained by the leveling for geoid height can be obtained at each point geoid For ellipsoid gap. Therefore, from a theoretical point of view, trigonometric leveling is also a means of measuring the shape of the earth, it does not depend on any assumptions. But because people generally can not be measured with sufficient accuracy refraction coefficient, trigonometric leveling so far only for the determination of low-precision elevation. Improve Trigonometric Leveling measures are four: 1, shortened attention. When the length of 1000 meters line of sight, the refraction angle and usually only 2 "or 3." In such a distance on the right to trigonometric leveling, the accuracy with ordinary leveling fairly. 2, the observed vertical angle. 3, choose a favorable observation time. Under normal circumstances, the vertical angle observations around noon most favorable. 4, to improve eye level.