1.17.2. Methods of plane tabling

There are three steps to work with plane table; (i) Levelling the plane table, (ii) Centering the plane table, and (iii) Orienting the plane table.

There are three critical steps involved in working with a plane table:

1. Levelling: This involves ensuring that the plane table is perfectly horizontal, which is typically done using a spirit bubble tube.
2. Centering: This step involves placing the plane table precisely over a point of interest on the ground. A plumb bob is used to ensure accuracy in centering.
3. Orienting: This step is crucial for accurately representing the plan. It can be done using a magnetic compass to align the table or by using a back ray method to reference back to a known point.

Think of the plane table as a camera that needs to be level and precisely aimed at a specific target to take a good picture. Just as you level a camera and then focus on your subject, the surveyor levels the table and centers it above a point before orienting it to get the right view of the terrain.

The equipment required for plane table surveying are shown in Figure 1.38: There are four methods of plane table surveying: (i) Radiation, (ii) Intersection, (iii) Traversing and (iv) Resection.

In plane table surveying, after setting up the table, there are four principal methods to gather data:

1. Radiation: This method uses distance and direction to locate objects. The surveyor measures distances to various points from the table's position and draws lines (rays) to mark these positions on the map.
2. Intersection: Used to locate points that are not directly visible. The surveyor measures angles from two known locations (stations) on a baseline and draws intersecting lines to pinpoint the position of an object.
3. Traversing: This method is employed when visibility is limited, allowing for the recording of points by moving the table to several stations.
4. Resection: This technique determines the position of the plane table when the location is unknown by back-sighting on two or three known points.

Imagine you are navigating a new city without a GPS. Radiation is like getting directions from a landmark. Intersection is like figuring out your location by viewing two streets from a corner and finding where they meet. Traversing is akin to walking down a street and taking notes on the sights along the way, and resection is like trying to figure out where you are by referencing several visible buildings.

Now-a-days, plane tabling is considered as obsolete, and therefore is not carried out in the field. The field data is directly collected and stored using either Digital Levels, GPS or Total Station, and mapping is carried out using the capabilities of the software in a computer.

In present times, the traditional method of plane tabling has largely been replaced by advanced technology. Methods like Digital Levels, GPS, and Total Stations offer much faster, more efficient, and precise data collection and mapping capabilities. These modern tools streamline the process by directly collecting and storing data, which can then be processed through specialized mapping software on computers, eliminating the labor-intensive steps of the plane table method.

Consider the difference between using a traditional film camera to capture images and using a digital camera today. While both can produce photos, digital cameras are faster, easier to use, and allow for instant editing and sharing. Similarly, modern surveying techniques have surpassed plane tabling in efficiency and ease of use.

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