MODERN SYSTEMS IN SURVEYING AND MAPPING

MODERN SYSTEMS IN SURVEYING AND MAPPING

Significant developments in the last three decades resulting in a variety of sophisticated instruments have revolutionized the techniques of conventional surveying and mapping. Such innovations are still continuing, leaving behind the conventional methods and making them out dated. As the technological development in instruments and processing techniques is so phenomenal that is difficult to discuss these comprehensively, therefore only brief description of some of the modern instruments and terminology associated with measurement of quantities such as length, area, volume, and coordinates of the points, has been presented in this chapter.

1.     ELECTRONIC DISTANCE MEASUREMENT INSTRUMENT (EDM)

Recently scientific advances have led to the development of electro-optical and electromagnetic instruments which are of great value to the surveyor for accurate measurements of distances. The electronic distance measuring (EDM) equipment which can be used for traverse, triangulation, and trilateration as well as for construction layout, is rapidly supplanting taping for modern surveying operations except for short distances and certain types of construction layout.

            Electronic distance measurement instruments utilize either infrared (light waves) or microwaves (radio waves). The microwave system requires a transmitter/receiver at both ends of the line to be measured, whereas the infrared systems require a transmitter at one end and a reflecting prism or mirror at the other end. Microwave systems have a usual upper measuring range limit of 50km. Although the microwave systems can be used in poorer weather conditions (fog, rain, etc) than infrared systems, the uncertainties caused by varying humidity conditions over the length of the measured line, result in lower accuracy expectations.

            Infrared systems come in long range (10-20 km), medium range (3-10km), and short range (0.5-3km).

            EDM can be mounted on the standards or on the telescope of most theodolites; additionally they can be directly mounted on the tribrach. EDMs measures slope distance between two points if at different elevations. The slope distance is reduced to its horizontal and vertical equivalents using the slope angle between the two points. EDMs when used with a theodolite, they can provide both horizontal and vertical position of one point relative to another.

            EDMs have built in or add-on calculator/microprocessors which provides horizontal and vertical distances.

ELECTRONIC THEODOLITE

The most modern theodolite contain circular encoders which sense the rotations of the spindles and the telescope, convert these rotations into horizontal and vertical angles electronically, and display the values of the angles on liquid crystal displays (LCD) or light emitting displays (LED).  These readouts can be recorded in a conventional field book or can be stored in a data collector for future printout or computations. The circles can be set to zero readings by simple press of button on the instrument. The horizontal circle readings of some of the electronic theodolites can be preset to any desired angle before a back sight is taken.

 ELCTRONIC TACHEOMETER OR TOTAL STATION

Electronic tacheometer or total stations are instruments which combine electronic theodolite and EDM instrument. They are equipped with a microprocessor for reduction of observed data. Electronic tacheometer can display horizontal angle, vertical angle, slope distance, horizontal distance, difference in elevation, and coordinates. The data can be stored in some form of storage device for further computations using an electronic computer.

LASER THEODOLITE

Laser theodolites have all the functions of electronic theodolite with facility of more accurately bisecting the target. By means of cross hairs the laser adaptor enables the observer to centre the laser beam very accurately on the target. The cross hairs can also be rotated as desired.

            Laser theodolite has a wide range of applications including tunneling and mining, piling and fencing, base-line surveys, marking and locating in space, shipbuilding and night surveying etc.

AUTOMATIC TOTAL STATION

The total station described previously is a manual one in the sense that it requires persons, i.e., the surveyor and a rod man holding the reflecting prism or mirror. A surveyor always requires some communication system to communicate with the rod man. Another disadvantage of these total station is that sighting the prism is not only time taking job but also less accurate. The automatic total stations overcome these problems. Automatic total stations have motorized EDM and theodolite. It can align itself in any specific direction very accurately (up to 0.5’’). by combing automatic target recognition (ATR) with motorized system, survey is reduced to a single men’s job. The instrument once aligned to prism or reflector, automatically tracks the movement of rod man and is controlled by rod man. It eliminates the need of communication system as the operator of the instrument is rod man himself.

            Automatic total stations are particularly very useful in areas of less vegetation and setting out jobs.

LASER ALIGNMENT INSTRUMENT AND ELECTRONIC LEVEL

Laser (light amplification by stimulated emission of radiation) alignment instrument produce a laser beam which is a visible straight line, used for alignment and setting out works in roads and railways. They are also used in the construction of large buildings and alignment of river dams. Laser beam can be used as plumb line. It can generate a reference plane for measurements of inclination and settlements, area leveling or profiles. Laser beam can also be placing pipe lines and monitoring machines in direction and elevation.

            Laser attachments are also available which can be mounted onto the telescope of theodolite transforming them to laser instruments.

            Laser beam instruments can be used in darkened areas indoors without a beam detector.

DIGITAL LEVEL

The digital levels use bar-code shafts. After targeting the staff, the reading is taken automatically and displayed. The measurements can be recorded in the field and down loaded into a computer for processing using the software provided with the instrument. Digital levels permit measurements to be made even when light conditions are inadequate. The staff section to be illuminated can be selected by moving the illuminator up or down.