Hello. This lesson is devoted to geometric leveling. Geometric leveling is a topometric method that can be used on the construction site, the construction, that can be used for supervision, structural monitoring, and also for all the work of measurement, whether it is the parcel measurement or the national measurement. With geometric leveling, we treat the problem of altitudes,.. which is a fundamental dimension for topometry. You see in this image a altimeter benchmark with a measurement rod that we will discuss later. The principle of geometric leveling. You have for example a field, which I draw here, and two points of interest where we want to determine a height difference between these points. We have here an initial point, which is the point A, here we have point B, and on the vertical of these points, I can draw here a straight line... materializing this vertical on A and B. Then, I can define a horizon, somewhere here, a horizontal line, and if I am able to measure the height from point A... and the height here from point B, the height difference, so the ΔHAB will be my hB minus hA. To achieve this, I will use a leveling rod that will be placed here on the vertical of point A, respectively to the vertical of point B, and to determine the measurement, I will use a level that I place here at the center with a spotting scope and a tripod to be able to put it down. Thus I have the measuring device that permits me to determine the height difference between point A and B. In this lesson, we first look at the definitions, what is an altitude? Then, we look at the principle of measuring with a level and one part is also devoted to control of the device. And finally, we will address the issues of tracking, how to concretely on a construction site or between a point of interest and another are we able to measure the height differences to determine the altitudes. Before addressing these issues in detail, let us look at the equipment and the device we use to make these measurements. Firstly, we have the level itself which is a scope with an optical axis here, there is a lens, an eyepiece, there is a reticle in the center realizing the center of the optical axis, and the scope is placed here on a base that is equipped with leveling screws in order to horizontalise and adjust the level. To measure, we will use a leveling rod here, with a graduation that will be explained later, which enables us to measure the heights relative to the point of interest to the millimeter. For geometric leveling, we arrange the level and the rod, and we will describe here the different parts of the level. We have first, in the lower part, a base that rests on the leveling screws. On this base, we have a spherical bubble and by the help of the screws we are able to adjust the base, that means creating a horizontal plane that the level rests on. The level is composed of a scope with a lense here, an eyepiece and a reticle that create the line of sight. On the level, or within depending on the model, we have a bull's eye level that enable us to make a precise wedge of the axis of sight so that it is horizontal and allows reading on the rod here on the vertical rod. The level. Presentation of the instrument. Here is the base, the leveling screws that there are three off. The horizontal circle for fast measurements of direction. The scope that pivots around the principle axis. The Bull's eye level for rough levelling. The line of sight. The adjustment screws for sharpness of the reticle. The screw for focus. And the screw for a lateral displacement at the end of the line of sight. You will now see a small video of an outdoor workshop that presents a practical stationing of the level. Leveling. Setting up the level and reading of the measurement rod. Firstly, the operator place the level on its tripod then brings it halfway between the two points to be leveled. Here, they are are the two first points of a traverse, a bolt and an intermediate point materialized by a armchair. In parallel, the operator place the measuring rod on the first point to be measured. Then, the operator proceeds to calibrate the equipment. The rough calibration is done using the foot-screws that allow to place the spherical bubble into his markers. On this level, the fine calibration is assured by a compensator. The level is now ready for use. The operator also stabilize the rod vertically if possible through a spherical bubble. The operator aim the rod, do the focusing and sets the sharpness of the reticle. He then proceeds to the measurement.