Plane table surveying is a type of surveying which can be done very fast. The necessary equipment of the plane table survey is mentioned below. Also, brief discussion and photographs of major instruments are given below.
General Plane Table Survey Equipment
Some basic surveying instruments are required for plane table surveying. Followings are the general plane table survey equipment.
Plane table
Alidade for sighting (telescopic or simple)
Plumb bob and plumb fork
Compass
Spirit level
Chain
Ranging rods
Tripod
Drawing sheet and drawing tools
Paper clips or screws
Details of Major Plane Table Survey Equipment
Simple Alidade
Alidade compass has two edges. One straight and other one is beveled. The straight edge is made of brass or gunmetal and works as a ruler. The beveled edge 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 vanes is the sight vane or the eye vane. It has three equidistant narrow silts. The surveyor looks through these silts towards the object or station. The other vane which is known as object vane is open and a fine thread is stretched between the top and bottom silt.This thread is used to establish a horizontal line of sight parallel to the ruler. The problem with simple alidade compass is that it can be used only when the elevations of the objects are low.