Composite Geometric Leveling 

The compound geometric leveling consists of a series of leveling simple geometries, properly tied to one another. This process is used when it comes to leveling in terrain of marked gradient, where the determination of the total level difference requires more than one station of the unit. It is desired to determine the difference in level from A to B and, in the case of terrain, no matter how well the device is positioned on the ground, it is not possible to aim the considered points, since the difference in level between points A and B is greater than the height of the sight, as shown in fig. 1

Figure 1

Thus, with the level in station 1, it is aimed at the aim placed at point A, which will represent the reverse reading. The fore-and-aft reading is then made at point M; as this will be the last forward look with the level in station 1, it will be called the "forward change". The level is then changed to station 2, from which a backsight at point M will be made and then a forward look at point B. In this way, it was concluded that in order to achieve the objective, two simple geometric leveling were carried out at station 1, properly connected by the shift stake M, in which if the change-of-place visas, and the station's reverse look-up 2; finally, the composite geometric leveling is achieved. 

In order to compensate for errors in a leveling, it is necessary to start and finish at the same point. As usual, the profile leveling is done, or open polygonals, after the leveling of each of the picket points in a profile, another leveling is performed in the opposite direction, so-called "counter-leveling”, when only a few of the points are leveled; and "re-leveling" when the return is done by leveling all points. 

2.1. Calculation of Geometric Leveling 

The quantities measured in a geometric leveling are recorded in a spreadsheet, and then the calculations are performed. The example of Fig. 2 is leveling and counter-leveling of a profile, where the dimension of point A is known, equal to 50,000 m, and the space between pickets is 20 m. 

Spreadsheet:

Figure 2

 2.2. Longitudinal profiles

 The longitudinal profile with a 10-fold exaggeration is the graph of an altimetric survey, as seen in fig. 3

Figure 3 

2.3. Calculation of the grade in a leveling profile

Grade is the line that accompanies the profile, with a certain slope, and which shows how much soil should be cut or filled.

Red quota (CV): vertical distance between any point of the grade and a point of the field. It can be positive (landfill) or negative (cut).

Waypoint: When the grade point coincides with the terrain point, with no cut or landfill (point C).

Declivity of the Grade: d = (HIGHER QUOTE - LOWER QUOTE) / DH

d (%) = (DN/DH). 100

Figure 4

2.4. Linking to the altimetric network

Level or equipotential surface is the surface along which the force of the gravity performs zero work; the Earth's equipotential surfaces are, in all its points, normal to the vertical of the place. The equipotential surface of level zero, considered as the reference surface, is the equipotential surface of the mean sea level, extended across the continents, ie is the geoidal surface.

Altitude is the height of a point on the ground in relation to the mean sea level and by quota to the height of the point in relation to an arbitrary horizontal plane. Thus, when the level reference is any surface, it is said that the level is apparent. The level is said to be true when the mean sea level is the reference.

See also   #PART 2