Fundamentals of Surveying PDF

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Name: _________________________ Group No.: ________________ Course & Year: _________________ Date Performed: ___________ Schedule: ______________________ Date Submitted: ___________ PR-LABORATORY-NO.1 CONVENTIONAL SURVEYING INSTRUMENTS I. Objective: To familiarize the different conventional surveying instruments II. Conceptual Background: For many years, the mankind has been using different surveying tools and equipment in order to gather accurate information about the land. Even in ancient times, people have been using old and archaic techniques for surveying. Land surveying has been done in various ways and with various tools and equipment, like the metal chain which was used in ancient times for measuring the distances from one point to another. Today, the surveying tools and equipment are far more technologically advanced and play a crucial role in every construction project. Without proper surveying equipment, accurate data cannot be gathered and success cannot be achieved. This is one of the many reasons why the surveying equipment has been used heavily throughout the years everywhere in the world. Having the proper tools and equipment is essential for the surveying process. The most commonly used surveying tools by the surveyors are: EDM’s digital levels, digital theodolites, GPS tools, data collectors, total station, etc. Each device has its own unique characteristics and is used combined with other surveying tools. For example, the total station is installed on a tripod and it measures the angle and the distance between two points. The GPS technology is the most advanced surveying technique available to surveyors. Therefore, it is most commonly used for the surveying processes because it provides precise and accurate data. By using the information provided by the satellites which orbit around the Earth, the GPS tools enable the land surveyors to find and measure points on the ground with high precision. Today the job of the land surveyors, thanks to the technological innovations, is far more easier than before. Worldwide, the land surveyors benefit heavily from the usage of modern and state of art surveying equipment. This equipment, available to them, is likely to be improved and to become even better with time (Alex Green, 2014). III. Equipment: Drawing tools IV. Procedure: Draw the following surveying instruments commonly used in field work: 1. Steel Tape: Tapes are made in a variety of materials, lengths and weights. Those more commonly used by the surveyor and for engineering measurements are the steel tapes, sometimes called the engineer’s or surveyor’s tape, and woven non-metallic and metallic tape. Steel tapes, for most surveying operations are graduated in feet or meters together with decimal parts of these units. Their lengths vary from 50 to 300 ft Fundamentals of Surveying Page 1 of 7  and form 15 to 100 m although the 100-ft and 30-m tapes are the most common lengths. Metric tapes are usually graduated to decimetres throughout with an end decimetre divided into millimetres. The cross-section of a steel tape varies, depending upon its total length and the type of service it is designed to withstand. For very precise measurements, such as those for base lines and in city surveys, the invar tape has come into general use. Invar is a composition of nickel and steel with a very low coefficient of thermal expansion, and is affected little by temperature changes. 2. Taping Accessories: a. Range Poles Range poles, sometimes called flags or lining rods, are used as guides or markers when sighting points and for lining up tapemen in order to keep them going along the correct direction. They are usually from 1 to 3 cm in diameter (some are hexagonal) and from about 2 to 3 m in length. Range poles are usually painted with alternate bands of red and white to make them more easily visible. The bands are each 30 cm in length which can be used for rough and quick measurements. b. Chaining Pins Chaining pins are sometimes referred to as taping (or surveyor’s) arrows. They are used for marking the ends of tapes or intermediate points during taping. Chaining pins are usually made of no.12 steel wire and are sharply pointed at one end. These pins have round loops (or eyes) at one end, are sometimes painted with alternate red and white bands, and are conveniently carried by a tapeman on a wire loop or ring. Strips of colored cloth are tied to the eyes to make the pins easily visible in weeds or tall grass. A set of eleven pins carried on a ring is standard. c. Tape Thermometer In precise taping operations, a thermometer is attached to the tape for the purpose of determining the temperature during actual taping. Thermometers for field use are about 12 cm long, graduated from -10 °C to 50 °C in 1° divisions, and kept in a protective metal case. Tape thermometers used are so designed such that their bulbs come in direct contact with the tape. They usually have brackets with a small spring that presses the bulb against the tape. d. Spring Scale A spring scale is sometimes called a tension handle. It is used at the end of a tape for reading the pull applied to the tape during measurement. A complete unit consists of a wire handle, a locking device to fit the end ring of the tape, and a spring balance reading up to 15 kg in ½ kg calibrations. Spring scales are used only in precise taping work and are usually dispensed with in measurements of ordinary precision. e. Tape Clamping Handle To apply tension by a strong grip using a scissor-type action on any part of a steel tape, a clamping handle is used. It provides the tapeman a device for Fundamentals of Surveying Page 2 of 7  protecting his hands from injury when handling steel tapes with sharp edges. Pulling a tape at certain sections without a clamping handle may result in a slight bending of the tape which in turn causes kinks on it. f. Plumb Bob A plumb bob is used in taping to project a point on the tape down to the ground, or to project a point on the ground up to the tape. Plumb bobs used in surveying are usually made of bronze, weighing from 0.25 to 0.50 kg, and attached to a fish-line cord or string about 2 m long. They have sharp replaceable points and a device at the top to which a string may be tied. g. Tape Leather Thongs A tape thong is attached to the forward end of a steel tape to allow the tapeman a better hold in the tape during measurement. It is made of leather, about 10 to 15 cm long, and with a loop which can be inserted easily and comfortably into the wrist and hands of the tapeman. h. Wooden Hub/ Peg Wooden hubs, pegs or stakes about 1-1/2 inches by 1-1/2 inches by 12 inches are used in surveying to establish points on the ground. In engineering surveys they are driven into the ground and are used in staking out a building, to run road center lines, and in staking out lines or grades. The top of the hub is established by driving a nail or tack into it. 3. Dumpy Level The dumpy level is the most widely used direct leveling instrument. It consists of a telescope which fixes the direction of the line of sight and which can be rotated through 360 degrees in the horizontal, a bubble tube attached to the telescope, a leveling head which supports the telescope and permits the bubble in the tube to be centered, and a supporting tripod. The name “dumpy level” originated from the fact that formerly this instrument was usually equipped with an inverting eyepiece and was shorter than other levels of the same magnifying power. The instrument is simple in construction and has fewer parts to become worn or displaced. 4. Wye Level The telescope tube of the wye level is supported by two Y-shaped uprights fixed to a horizontal bar and in turn attached to the vertical spindle about which the instrument rotates. By releasing the two clamping collars which fit across the tops of the Y’s, the telescope can be lifted clear of the Y-supports. The wye level is simpler to adjust than a dumpy level since its telescope can easily be lifted from the wyes and turned end for end. It is, however, now almost obsolete and not commonly used since other levels are better constructed and satisfactory for leveling work. Although this type of instrument is not as popular as the other levels, many of its older models have more sensitive bubble tubes than the other dumpy levels. 5. Automatic Level Self-leveling features are incorporated in automatic levels. Rough leveling using a three-screw leveling head approximately centers a bull’s-eye bubble in most of these instruments. As soon as the bull’s-eye bubble is centered the line of sight is automatically leveled and kept leveled when a compensator takes over. A Fundamentals of Surveying Page 3 of 7  pendulum is employed to maintain continuously and automatically the line of sight in a horizontal position. Most automatic levels are comparatively expensive; however, they are very useful under conditions of unstable ground and wind, and where speed in leveling work is an important consideration. Because of the ease and rapidity in using automatic levels, they have become quite popular for general leveling operations. 6. Hand Level and Clinometer The hand level is a hand-held instrument consisting of telescope and level vial. It is used on reconnaissance surveys where extreme accuracy is unnecessary and in taping to determine if the tape is being held horizontally. It is used to advantage for estimating how high or low the engineer’s level must be set in order to be able to read the leveling rod. The hand level consists of a tube about 15 cm long through which the observer sights. On top of this tube is a small bubble reflecting through a prism so that it appears to move vertically as seen by the observer sighting through the tube at a level rod. There is no magnification by the hand level. The observer sees the rod through one part of the sighting tube and the bubble image is seen in the other part. When the bubble appears to be on the cross line it is in the center of the tube. The clinometer is simply a hand level adapted for measuring vertical angles. A vertical circle is added upon which angles may be read, and rise (or fall) per horizontal run. The clinometer is popularly used by foresters in determining height of tress by measuring the rates of grade to the top and bottom of the tree. The arithmetic sum of these multiplied by the distance to the tree gives the height. 7. Leveling Rods Leveling rods are used in conjunction with an instrument such as a transit or level to determine distances or differences in elevation. There are different kinds of the rods used in surveying. Some rods are made in one piece and others either hinged or telescoping, and are made of wood, fibreglass or metal and have graduations in feet and decimals, or meters and decimals. Also, a wide choice of patterns, colors, and graduations are available. The various types, usually named for American cities and states, include the Philadelphia rod, New York, Boston and Florida rods. Leveling rods are basically self-reading or target rods. Self-reading rods, which are the most commonly used, can be read by instrumentman while sighting through the telescope and noting the apparent intersection of the cross-hairs on the rod. A target rod has a circular or elliptical metal target plate divided into quadrants of alternating red and white colors. It is moved up or down under the direction of the instrumentman and is clamped and read by the rodman. The target is useful when difficulties are encountered in reading the rod directly when it is held in dimly-lighted places, when the sights are obscured by foliage, or when extra-long sights are required. The Philadelphia rod is the most commonly used type of rod. It is a combination of self-reading and target rod and consists of two sliding sections so that it can be extended to a length about twice the length of one section. The rear section slides with respect to the front section, and can be held in any desired position by means of a clamp screw on the upper sleeve. The rod is said to be a “short rod” when the rear position is not extended, and a “long or high rod” when it is extended. Experience shows that leveling done by reading the rod directly is practically as accurate as that done by reading the rod with a target. Fundamentals of Surveying Page 4 of 7  8. Engineer’s Transit The transit is essentially a telescope and two large protractors, one protractor mounted in a vertical plane the other in a horizontal plane, fixed to measure the angle of rotation of the telescope about the horizontal and vertical axes, respectively. Its three main parts are: the upper plate, lower plate, and leveling head. Some of the modern types of transit differ considerably in design and construction from those long in use but their essential features do not differ greatly, and their use not at all. The engineer’s transit is sometimes referred to as the “universal instrument”, because of its variety of uses. These include the measurement of horizontal and vertical angles, approximate distances, differences in elevation by direct leveling, and direction by the built-in compass box. The transit is also used for establishing and extending straight lines. It is designed to give readings to the nearest minute of arc, but finer graduations are available and permit readings to 30, 20, 15, or 10 second. 9. Theodolite The theodolite is a precision surveying instrument for measuring angles. There are two general classes of theodolites: repeating theodolites and direction theodolites. Repeating theodolites are precise transits which can read to 10 seconds or less. A direction theodolite is a non-repeating type of instrument which has no lower motion. Dircetions rather than angles are read. After a sight has been taken on a point, the direction of the line to the point is read on the circle. An observation on the next mark gives a new direction. The angle between the lines can be found by subtracting the first direction from the second. 10. Plane table The plane table is composed of a drawing board mounted on a tripod so that it can be set up in the field and leveled. A sheet of drawing paper, called a plane-table sheet, is fastened to the board. The board may be rotated about the horizontal plane after leveling. It is set up at waist level to allow the surveyor to bend over it easily without leaning on any part of it. The primary used of the plane table is in field compilation of maps. By means of the plane table, points on the ground to which observations are made can be plotted immediately in their correct positions on the drawing, all angles being plotted graphically. The plane table method of surveying is especially adapted to securing details of the map. It is a valuable and commonly used means of completing the compilation of maps from aerial photographs, particularly where the ground is hidden by thick overgrowth. It also provides a simple and versatile method for establishing supplementary control elevations. 11. Alidade The alidade is a combination of a straight edge and a sighting device. It consists of a telescope supported by a pedestal rigidly attached to a base or blade. The telescope is similar to that of a transit and is equipped with a vertical and a horizontal cross-hair, and two stadia hairs. A sensitive level vial and bull’s-eye level, a vertical arc and/or Beaman’s arc, a compass needle, and lifting knobs are also provided. The telescope may be centered over the blade, or be offset to place the line of sight Fundamentals of Surveying Page 5 of 7  along the edge. Aside from plotting angles graphically, the alidade can be used to determine horizontal, vertical and inclined distances by the stadia method. 12. Subtense Bar The subtense bar is a device used for determining distances indirectly. It consists of a bar made from an alloy having a low coefficient of expansion. The instrument is mounted horizontally on a tripod and aligned perpendicular to the line by means of a sighting device on top of the bar. The bar is leveled by means of a bull’s-eye level and leveling screw. Fixed targets near the ends of the bar are exactly 2 meters apart. A transit or theodolite is used to measure the subtended angle between these two targets, and must be capable of measuring to one second of angle or less. The horizontal distance from the transit or theodolite to the bar is equal to one-half the distance between the targets multiplied by the cotangent of one-half the angle subtended by the targets. Accuracy of 1/1000 to 1/5000 may be attained by taking several readings of the angle at both ends of the line. 13. Sextant The sextant is an angle measuring instrument, held in the hand of the user. It functions by the physical principle that a light ray striking a plane mirror causes the angles of incidence and reflection to be equal. By sighting through the small telescope, and adjusting the movable arm until the correct reflections of the objects being sighted appear in the mirrors, the angle between these objects is measured. Because it is not necessary for the observer to remain stationary during observation, the sextant is well suited for hydrographic work and has the added advantage of measuring angles in any plane. It is used principally by navigators and surveyors for measuring angles from a boat, but it is also employed on exploratory, reconnaissance, and preliminary surveys of land. The precision of horizontal measurement with the sextant depends upon the size of the angle and upon the length of sight. Hence, the sextant is not an instrument of precision for measuring small angles and where short distances are involved. 14. Planimeter The polar planimeter is a mechanical device used to determine the area of any shape of figure, bounded by straight or curved lines, if the figure is plotted to a known scale. This device utilizes the relationship between the tracing arm which traces the outline and the connected recording wheel which records the area which the tracing arm has traversed. The planimeter mechanically integrates are and records the answer on a drum and disk as a tracing point is moved over the outline of the figure to be measured. The instrument touches the scaled figure at only three places: the anchor point, the drum, and the tracing point guard. Its major parts are a scale bar, graduated drum and disk, vernier, tracing point and gurad, and anchor arm, weight, and point. The scale bar may be fixed or adjustable. The planimeter is most useful for determining irregular areas, areas of road cross- section and in checking computed areas in property surveys. The precision of the resulting area is dependent on the scale to which the figure is drawn, and on the skill of the operator of the planimeter. With care, areas that are accurate within one percent can be obtained by means of the planimeter. s 15. Geodetic Total Station Fundamentals of Surveying Page 6 of 7  A geodetic total station instrument consists of an electronic distance measuring instrument, an electronic digital theodolite, and a microcomputer. They are also referred to as electronic tacheometer. This type of instrument has the capability to simultaneously measure distance, as well as direction, and transmit the result automatically to a microcomputer. They are a relatively new development in the field of surveying. The instrument can be operated to send out a high-frequency microwave or a beam of light (modulated at perfectly regular intervals) from one end of a line to be measured, and directs it toward the far end of the line. At the other far end a reflector or transmitter-receiver reflects the microwave or light back to the instrument. Electronical analysis occurs within the total station to give the distance between the two points. The usual carrier used in most total station instruments are tungsten, mercury, laser or infrared light which is intensity modulated at a very high frequency. The keyboard is the link between the operator and the microprocessor. Through the keyboard, the operator can cause the display of the slope distance, horizontal distance, difference in elevation, horizontal angle, and the vertical angle. Observed data can also be stored in the data storage unit and later retrieved when needed. Display outputs can be recorded on either paper or magnetic tape for further calculations in a computer. Total stations are extremely versatile and useful for almost all types of surveys. A number of totals station instruments are currently available. The total stations are, however, very expensive and are not likely to have wide application to large-scale surveying work in the immediate future. This modern instrument is fully automatic to such extent that, after the instrument and its reflector have been set over the two ends of the line to be measured, the operator need only depress a button, and required data easily displayed. 16. Reflectors and targets A reflector is a device used with an EDM instrument when a continuous beam of light needs to be transmitted during the measurement of distances. The EDM is located at one end of the line to be measured, and the reflector occupies the other end of the line. The reflector used consists of one or more prisms which return the light beam precisely to its source. In the case of microwaves, a repeater is used. The repeater is very nearly like a transmitting station except that after a predetermined momentary delay, it returns a microwave beam like the one received. The combined target/reflector can be mounted and force-centered on a compatible tripod or can be connected to a hand-held centering rod when many sights are being taken from a single set up. V. Output: Fundamentals of Surveying Page 7 of 7