plane table survey | easy to remember

Plane Table Survey

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lane Table Survey: Introduction, principle, instruments, setting up the plane table, methods of plane tabling, advantages, sources of Errors.
• Plane Table Surveying is a graphical method of survey in which the field observations and plotting are done simultaneously.
 • It is simple and cheaper than theodolite survey. It is most suitable for small scale maps.
• The plan is drawn by the surveyor in the field, while the area to be surveyed is before his eyes. Therefore, there is no possibility of omitting the necessary measurements.

Equipments and Accessories for Plane Tabling

The following instruments are used in plane table surveying.

Equipments

• Plane Table
• Tripod
• Alidade

Plane Table: The drawing board for plane tabling is made from well-seasoned wood with its upper surface exactly plane.
• It is normally rectangular in shape with size 75 cm x 60 cm
• It is mounted on a tripod and clamps are provided to fix it in any direction. The table can revolved about its vertical axis and can be clamped in any position, when necessary.

Accessories

• Trough Compass
• Spirit level
• U-Fork with Plumb bob
• Water proof cover
• Drawing paper
• Pins
• Drawing accessories

Tripod

also read :- what is surveying

• The plane table is mounted on a tripod
• The tripod is generally of open frame type, combined rigidity with lightness. The tripod may be made to fold for convenience of transportation. }
• Tripod is provided with three foot screws at its top for leveling of the plane table.

Alidade

• The alidade is useful for establishing a line of sight.
• Two Types of alidade are used.
• Simple alidade
• Telescopic alidade

Simple Alidade

• It is used for ordinary work
• It is generally consists of a gun metal or wooden rule with two vertical vanes at the ends.
• The eye-vane is provided with a narrow slit while the object vane is open and carries a horse hair. Both the slits, thus provide a definite line of sight which can be made to pass through the object to be sighted
• To draw the rays, one of the edge of alidade is beveled and this perfectly smooth working edge is known as the fiducially edge.
• The fiducially edge is graduated to facilitate the plotting of distances to a scale.

Telescopic Alidade

• The telescopic alidade is used when it is required to take inclined sights.
• It essentially consists of a small telescope with a level tube and graduated arc mounted on horizontal axis.
• It gives higher accuracy and more range of sights.