🕑 Reading time: 1 minuteSometimes special surveying instruments are required for specific purposes in civil engineering surveys. Types of these special surveying instruments with their uses are discussed in this article. There are many general surveying instruments such as compass, levels, theodolites etc. used for different operations. But there are some special surveying instruments with some specific purposes with different setups.
Types of Special Surveying Instruments and Their UsesThe special instruments used in surveying are:
- Jig telescope and jig transit
- Electronic theodolite
Jig Telescope and Jig TransitIn olden days, conventional transit and levels were used for industrial surveying. In modern times, high precision surveying instruments are required. Hence jig telescope and jig transit are developed which are used for optical tooling. Jig telescope has optical micrometers which can measure to the 1000th of an inch.
TelemeterTelemeter is a special surveying instrument which directly measures the horizontal distance. It is attached to the telescope at objective end and corresponding to that a counter weight is attached at eye-piece end. Usage of telemeter is similar to tacheometer, but in this case readings are taken directly. Figure below shows the horizontal rod with Vernier which is used with telemeter. During field measurements, the image of the Vernier is brought into the middle and then micrometer drum is revolved until both Vernier and main scale graduations are coincided. The reading obtained by telemeter represents the slope distance along line of sight. If the inclined distance is L and angle of inclination is x, then horizontal distance is
D = L cosx