Question

After fixing the plane table to the tripod, the main operations which are needed at each plane table station are

(i) Levelling

(ii) Orientation

(iii) Centering

The correct sequence of these operations is

Iysu Vscy dks VªkbikWM ij fiQDl djus ds ckn] izR;sd Iysu Vscy LVs'ku ij ftu eq[; vkWijs'kuksa dh vko';drk gksrh gS] os gSa%

(i) lery djuk

(ii) vfHkfoU;kl

(iii) dsUnzhr djuk

bu lafØ;kvksa dk lgh Øe gS

(i), (ii), (iii)

(i), (iii), (ii)

(iii), (i), (ii)

(ii), (iii), (i)

Answer ( Option B)

(i), (iii), (ii)

Solution

At each station, the plane table is required to get set up before carrying out any plotting work. It basically consists of three operations: Fixing, Levelling and Centering.

Note:

For plane table surveying, Levelling is performed first, followed by Centering and then Orientation. For dumpy level, theodolite, and other instruments, Centering is done first.

(a) Fixing: The top of the tripod stand is fixed in level by eye estimation at a convenient height with its legs uniformly spread and shoes fixed firmly into the ground.

(b) Levelling: The top of the table is levelled by moving the legs of the tripod.

(c) Centering: There are two types of operations involved in the centering of the plane table.

• Centering with reference to the already plotted position of the station: The pointed end of the upper arm of a U-fork is held at the plotted position of the station and the table is shifted and adjusted in such a way that the tip of the plumb bob points exactly over the ground station.

• Centering with reference to the ground location of the station: The tip of the plumb bob attached to a U-frame is placed exactly over the ground point which is required to be transferred; The point corresponding to the tip of the pointed arm of the U-frame provides the transferred position on the table.

(d) Orientation: It is the process of a plane table survey of setting the position of the board at the survey station.