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1. Read and translate the text:

Geodetic Observing Instruments

Some of the most important geodetic instruments are the surveyor’s level, the theodolite and the tacheometer (or total station).

The surveyor’s level is used in surveying to measure the height of distant points in relation to some datum (usually, mean sea level). It consists of a telescope fitted with a spirit level and, generally, mounted on a tripod. It is used in conjunction with a graduated rod placed at the point to be measured and sighted through the telescope.

Here are the main steps in using the surveyor’s level:

Step 1: Find a reference point (benchmark elevation)

Step 2: Set up the surveyor's level

Step 3: Reading the leveling rod

Step 4: Taking readings

Step 5: Make a grid over the chosen plot

Step 6: Making sense of the collected data

Step 7: Drawing topography lines

The theodolite is a basic surveying instrument of unknown origin but going back to the 16^th-century English mathematician Leonard Digges. It is used to measure horizontal and vertical angles. In its modern form it consists of a telescope mounted to swivel both horizontally and vertically. Leveling is accomplished with the aid of a spirit level; crosshairs in the telescope permit accurate alignment with the object sighted. After the telescope is adjusted precisely, the two accompanying scales, vertical and horizontal, are read. Mounted on a tripod with adjustable legs, the theodolite is used in the field to obtain precise angular measurements for triangulation in road building, tunnel alignment, and other engineering work. The transit is a variety of theodolite that has a telescope so mounted that it can be completely reversed, or transited. The phototheodolite, a combination camera and theodolite mounted on the same tripod, is used in terrestrial photogrammetry for mapmaking and other purposes.

The tacheometer additionally determines, electronically or electro-optically, the distance to target, and is highly automated in its operations.

2. Answer the following questions:

1. What are the main geodetic instruments?

2. What is the surveyor’s level used for?

3. What does the level consist of?

4. Name the main steps in using the level.

5. When and by whom was the theodolite invented?

6. What are the theodolites used for?

7. What does the theodolite consist of?

8. What varieties of the theodolite are there?

9. What does the tacheometer determine?

3. Look at the picture below. Name the main parts of a theodolite. Translate into Russian.

4. Fill the table with the information from the picture:

Part of the theodolite	Its function

Text 7

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