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theodolite mounted on the same tripod, is used in terrestrial
photogrammetry for mapmaking and other purposes.
Electronic theodolites are widely used all over the world. The
horizontal and vertical angle measuring systems fitted into

____________ are made of glass circles with binary codes etched onto
them. Light is passed through these and the pattern emerging is
proportional to the angle through which the theodolite has been

rotated.
This is detected by an incremental encoder which converts the
varying light intensity into digital signals. These are converted into an
angular output by a microprocessor which is accessed through a

keyboard and display:

Figure 10.10. Optical Theodolite

_______________also measure horizontal and vertical angles and

have features very similar to electronic ones, but their reading systems
are very different and rely on manual operation and recording.

Task 2 Define which of the subtitles expresses the main idea of
the text:

1. What is theodolite?
2. Theodolites as the main instruments for angle measurement.

Their types and usage.
3. Application of theodolites.
4. Main types of theodolites and their functions.
5. The most important elements of digital and optical theodolites.

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