PLANE TABLE SURVEYING SURVEYING – I NUST Institute of Civil Engineering/Engr Muhammad Ammar

PLANE TABLE SURVEYING Plane Tabling is a graphical method of surveying in which the field work and plotting are done simultaneously. Useful to fill in details between stations fixed by triangulation or theodolite traversing. Particularly adapted for small scale or medium scale mapping in which great accuracy in detail is not required. The plane table consists essentially of: A drawing board mounted on a tripod and A straight edge called an alidade. NUST Institute of Civil Engineering/Engr Muhammad Ammar

SURVEYING – NUST Institute of Civil Engineering/Engr Muhammad Ammar

THE DRAWING BOARD Made of well-seasoned wood such as teak or pine. Size varies from 40cm x 30cm x 75cm x 60cm or 50cm to 60 m square. It is mounted on a tripod in such a manner that it can be leveled, and revolved about a vertical axis and clamped in any position. NUST Institute of Civil Engineering/Engr Muhammad Ammar

PLAIN ALIDADE Consists of a metal (brass or gunmetal) or boxwood straight edge or ruler about 50 cm long. The beveled (ruling or working) edge of the alidade is called the fiducial edge. It consists of two vanes at the ends, the vanes are hinged and can be folded when the alidade is not in use. One of the sight vanes is provided with a narrow slit and the other with a central vertical wire or hair. One of the vanes known as sight vane is provided with a narrow slit with three holes, one at the top, one at the bottom and one in the middle. NUST Institute of Civil Engineering/Engr Muhammad Ammar

PLAIN ALIDADE The other vane which is known as object vane, is open and carried a hair or a fine thread or a thin wire stretched between the top and bottom of the slit. With the help of the slit, a definite line of sight may be established parallel to the ruling edge of the alidade. The length of the ruling edge should be equal to the smaller side of the plane table. A plane alidade can be used only when the elevations of the of the objects are low. NUST Institute of Civil Engineering/Engr Muhammad Ammar

PLAIN ALIDADE Sight Vane Object Vane Fiducial Edge NUST Institute of Civil Engineering/Engr Muhammad Ammar

PLAIN ALIDADE NUST Institute of Civil Engineering/Engr Muhammad Ammar

TELESCOPIC ALIDADE The alidade which is fitted with a telescope is known as a telescopic alidade. It is used to take inclined sights. It increases the range and accuracy of the sights. It consists of a small telescope with a level tube. A graduated scale is mounted on the horizontal axis. One side of the metal ruler is used as the working edge along which lines are drawn. The angles of elevation or depression can be read on the vertical circle. NUST Institute of Civil Engineering/Engr Muhammad Ammar

TELESCOPIC ALIDADE NUST Institute of Civil Engineering/Engr Muhammad Ammar

SPIRIT LEVEL It consists of a small metal tube which contains a small bubble. The spirit level may also be circular but its base must be flat so that it can be laid on the table. The table is truly level when the bubble remains central all over the table. NUST Institute of Civil Engineering/Engr Muhammad Ammar

SPIRIT LEVEL NUST Institute of Civil Engineering/Engr Muhammad Ammar

THE MAGNETIC COMPASS A box compass consists of a magnetic needle pivoted at its centre freely. It is used for orienting the plane table to magnetic north. The edges of the box compass are straight and the bottom is perfectly flat. NUST Institute of Civil Engineering/Engr Muhammad Ammar

THE MAGNETIC COMPASS NUST Institute of Civil Engineering/Engr Muhammad Ammar

PLUMBING FORK The plumbing fork consists of a hair pin-shaped brass frame, having two equal arms. One end has a pointer while a plumb bob is attached the other end. It is used in large scale survey for accurate centering of the station location on the table over its ground position. NUST Institute of Civil Engineering/Engr Muhammad Ammar

PLUMBING FORK It is also used for transferring the location of the instrument station on the sheet on to the ground. The fork is placed with its upper arm lying on the top of the table and the lower arm below it. The table is said to be centered when the plumb bob hangs freely over ground mark. NUST Institute of Civil Engineering/Engr Muhammad Ammar

PLUMBING FORK Plumbing Fork NUST Institute of Civil Engineering/Engr Muhammad Ammar

ADVANTAGES OF PLANE TABLING It is most suitable for preparing small-scale maps. It is most rapid. The field book is not necessary as plotting is done in the field concurrently with the field work, and hence the mistakes in booking the field notes are avoided. The surveyor can compare the plotted work with the actual features of the area surveyed and thus can ascertain if it represents them properly. It is particularly advantageous in magnetic areas where compass survey is not reliable. It is less costly than a theodolite survey. No great skill is required to prepare a satisfactory map. NUST Institute of Civil Engineering/Engr Muhammad Ammar

DISADVANTAGES OF PLANE TABLING It is not suitable for work in a wet climate. It is heavy, cumbersome and awkward to carry. There are several accessories to be carried, and, therefore, they are likely to be lost. It is not intended for accurate work. If the survey is to be re-plotted to a different scale or quantities are to be computed, it is a great inconvenience in absence of the field notes. NUST Institute of Civil Engineering/Engr Muhammad Ammar