There is a lot of varieties of measuring (road landing) equipment. The range of the rangeference is present in almost any model theodolite. Thanks to it, such an additional option is being implemented as the definition of distance.

## Main nuances

The need to measure the distance by theodolitis occurs when a tachometric or horizontal shooting is produced. The denseard is a couple of range finding threads. The procedure is approximately as follows:

• First, the height of the device (theodolite) is set to the point of standing;
• Then the level rack is mounted on the place to which the distance is required;
• Support the pipe on the countdown close to the height of the device itself;
• Take references on two rangefinder threads (top and bottom);
• Determine the range of counting over the rangefinder using the special formula that takes into account the coefficient, the difference in the rake samples;
• The result is made in the log of tachometric shooting.

At the next stage, the horizontal position is set. To do this, in the process of receiving results, another formula is used, taking into account the angle of inclination of the sighting rays. To simplify work, using the theodolite with a reverse display, located on top of the long-air thread orient to close value (in decimeters).

This allows you to speed up the definition difference. But if the directolite type is used, then the tip must be done on the bottom thread.

## Theory and Principle

Non-a rangefinder, allowing to measure the lengths of lines, is present in the overwhelming majority of geodetic equipment models. The network includes a pair of main rangefinder threads. Their projection through the visual tube forms the angle of pararallax. At the same time, distance dividing the rangefinder threads and the focus of the lens are greatly practical. To measure the distance, apply raters with a centimeter scale.

First take a counting showing the number of centimeters visible through the visual tube separating the projections of the threads. The rangefinder coefficient is taken equal to 100. Judging by the available information, the accuracy of optical threaded rangers is about 1: 400 (0.25%) measured distances. For a more accurate dimmer of long lines, they advise them to split them on the segments of 50-100 m. With this approach, the error is reduced by 1.5-2.5 times.

Most often, the parallact angle is constant. In this case, to determine with the help of a rangefinder rail, the distance between two points should be folded:

• the gap from the edge of the focus to the rail;
• focal length;
• The distance between the lens and the axis of the torque of theodolite.

## What else do you need to know?

The so-called permanent terms of the rangefinder is rigidly and uniquely set in any design. Its value is a few centimeters; The exact indicator is provided in the rangefinder technical passport. When measuring large distances or low accuracy requirements, constant terms can be ignored. The consequence of the theory of the denselor is that during the measurement of the rail should be on the normal to the beam of Vizier. When measuring the inclined distance, the visible segment of the rail is replaced by another segment.

When due to obstacles (reservoirs, pita, buildings), the distance can not be measured with a ribbon, it is determined by an indirect technique. Be sure to check the control, building an additional triangle on the basis and then, if there is no excessively large discrepancies, it is necessary to calculate the arithmetic average. Nution, like any other rangefinder, works at the expense of “solutions” of a special long-shaped triangle amn.

MN side is customary to call the base, and the angle opposite is a parallact angle. Most often, the angle of pararallax is small.

Measurement of the distance in devices with a constant base and changing angle are carried out taking into account the radian painted in the angular seconds. But often use rangefinders with a stable angle and a replacing base. If internal focus is provided, the focal length change, moving the focusing component. In this case, the formula for determining the distance, which includes the coefficient, the result of the range-ranking on the rail and the correction. The level of the correction is selected by an experimental way using a horizontal basis up to 150 m long.

This distance is divided into segments of 10 m. To compensate for at least partially the impact of vertical refraction, use horizontal rails. Then you will have to place rangefinder threads horizontally (with respect to the pipe grid). The amendment to bring the line to the horizon is determined with the tilt of the horizon line. The denseard can measure the line with a maximum length of 300 m, while the error can reach 0.3%.

It may seem that this value is too large. But in fact, for topographic and geodesic filming, such an error is quite acceptable. You can use a native rangefinder and to solve a number of other tasks arising in engineering geodesy. IMPORTANT: Sometimes the generally accepted coefficient 100 for such an appliance turns out to be incorrect and does not give good results. In this case, the real accurate coefficient is calculated by sharing the focal length of the interval from one to another rangefinder thread.

A set of some threaded rangers includes coarse racks with centimeter divisions. When the light rays, having leaving the rangefinder threads, pass through the lens in the front focus, they fall on the rail at two points. The coefficient 100 is convenient if the parallactic angle is 34.38 degrees.

With the difference from this indicator, of course, it is necessary to carry out additional calculations. But then calculate the exact distance in meters and get integers is unlikely to succeed.

In the next video you are waiting for the measurement of horizontal angle by theodolite.

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