Distance meter on the ground. Methods of measuring distance

Distance measurement is one of the most basic.tasks in geodesy. There are different ways to measure the distance, as well as a large number of instruments created to carry out these works. So, consider this issue in more detail.

Direct distance measurement method

If it is necessary to determine the distance to the object in a straight line and the terrain is available for research, a simple distance measuring device such as a steel tape measure is used.

Its length is from ten to twenty meters.A cord or wire can also be used, with white notation after two and red after ten meters. If it is necessary to measure curvilinear objects, an old and well-known two-meter wooden compass (sazhen) is used, or, as it is also called, “Kovylek”. Sometimes it is necessary to make preliminary measurements of approximate accuracy. Do this by measuring the distance in steps (at the rate of two steps is equal to the height of the measuring minus 10 or 20 cm).

Distance measurement on the ground remotely

In case of finding the measurement object in the zoneline of sight, but if there is an insurmountable obstacle that makes direct access to the object impossible (for example, lakes, small rivers, swamps, ravines, etc.), distance measurement is applied remotely by a visual method, or rather methods, since there are several varieties:

1. Highly accurate measurements.
2. Low current or approximate measurements.

К первым относятся измерения при помощи special devices, such as optical range finders, electromagnetic or radio range finders, light or laser range finders, ultrasonic range finders. The second type of measurement is a method such as geometric eye. Here and determine the distance from the angular size of objects, and the construction of equal right-angled triangles, and the method of direct serif in many other geometric ways. Consider some of the high-precision and approximate measurement methods.

Optical distance meter

Such distance measurements with millimeter accuracyin common practice are needed infrequently. After all, neither tourists nor military intelligence officers will not carry with them overall and heavy objects. Basically, they are used during professional geodetic and construction work. Often use this instrument for measuring distances, such as an optical range finder. It can be both with a constant and with a variable parallax angle and can be a nozzle to an ordinary theodolite.

Measurements are made on vertical andhorizontal measuring rails with a special installation level. The accuracy of measurements of such a rangefinder is quite high, and the error can reach a value of 1: 2000. The measurement range is small and ranges from only 20 to 200-300 meters.

Electromagnetic and Laser Rangefinders

Electromagnetic distance meter refersto the so-called pulse-type devices, the accuracy of their measurement is considered average and may have an error from 1.2 to 2 meters. But on the other hand, these devices have a great advantage over their optical counterparts, since they are optimally suited for determining the distance between moving objects. Their distance units can be calculated in both meters and kilometers, so they are often used in aerial photography.

As for the laser range finder, itdesigned to measure not very large distances, has high accuracy and is very compact. This particularly applies to modern portable laser roulettes. These devices measure the distance to objects at a distance of 20-30 meters and up to 200 meters, with an accuracy of no more than 2-2.5 mm over the entire length.

Ultrasound rangefinder

This is one of the most simple and convenient devices.It is light and easy to use and refers to devices that can measure the area and angular coordinates of a specific point on the ground. Nevertheless, apart from the obvious advantages, he also has disadvantages. Firstly, due to the small measuring distance, the unit for measuring the distance of this device can be calculated only in centimeters and meters - from 0.3 to 20 meters. Also, the accuracy of the measurement may slightly change, since the speed of sound transmission directly depends on the density of the medium, and, as is known, it cannot be constant. Nevertheless, this device is great for fast small measurements that do not require high accuracy.

Geometric eye methods for measuring distances

Above we talked about professional methods of measuringdistances. And what to do when there is no special distance meter at hand? Here geometry comes to the rescue. For example, if it is necessary to measure the width of a water barrier, then two equilateral right-angled triangles can be built on its bank, as shown in the diagram.

In this case, the width of the AF river will be equal to the DE-BF. Angles can be aligned using a compass, a square piece of paper, and even using the same crossed twigs. There should be no problems.

You can still measure the distance to the target throughthe obstacle, using also the geometric method of direct serif, constructing a right triangle with a vertex on the target and dividing it into two different ones. There is a way to determine the width of the barrier with a simple blade of grass or thread, or a method with an exposed thumb ...

It is worth considering this method in more detail, sincehe is the easiest. A noticeable object is selected on the opposite side of the barrier (it is necessary to know its approximate height), one eye closes and a raised thumb of an outstretched hand is pointed at the selected object. Then, without removing the finger, close the open eye and open the closed one. The finger is obtained in relation to the selected object is shifted to the side. Based on the expected height of the object, approximately how many meters visually moved the finger. This distance is multiplied by ten and the result is an approximate width of the barrier. In this case, the person himself acts as a stereophotogrammetric distance meter.

Geometric methods for measuring distancea lot. What about each to tell in detail, it will take a lot of time. But they are all approximate and are suitable only for conditions when accurate measurement using instruments is impossible.