Plane Table Surveying
Plane table surveying also refer as Plane tabling, is a method of surveying in which field-work and office-work are do same time on the plane table. The field observations are taken and record side by side on the sheet fix upon the plane table and a map of the area is obtain.
It is commonly employ for small and medium scale mapping of comparatively large areas where great accuracy is not the main consideration such as for topographical surveys.
The equipment essentially need for a plane tabling is a plane table or drawing board which carries a drawing sheet.
It is mount on a tripod stand and an alidade which provides line of sight and a straight graduate edge.
Advantages of Plane Tabling
- It is one of the most rapid methods of surveying.
- Field-notes are not require, and thus the possibility of mistakes in booking is eliminate.
- Measuring of lines and angles is mostly dispense with since they are obtain graphically.
- Since the map is plot in the field, there is no chance of omitting necessary measurements.
- The surveyor is fully confident about the true representation of the area since he can always compare his work with the actual features on the ground and cannot, therefore, over-look any essential detail.
- The surveyor can check the accuracy of his work more frequently and from any position he may desire, thus eliminating all errors at the spot.
- It is particularly suitable for filling in details in hilly areas and in magnetic areas where chain and compass, surveys are not suitable.
- Contours and other irregular objects may be accurately represent on the map since the tract is in the view.
- It is less costly than theodolite survey.
- No great is require in making a satisfactory map and the work can be entrust even to a subordinate.
Disadvantages of Plane Tabling
- It is unsuitable for work in a wet climate and is difficult in high wind.
- It is not useful for large scale surveys and accurate work.
- Not suitable for surveying a densely wooded area.
- The instrument is heavy and cumbersome and the various accessories, being loose, are likely to be lose.
- The absence of field-notes is sometimes inconvenient if the survey has to be replotted to a different scale.
- Only day time can be avail of for the field and plotting work whereas in other methods of surveying, day time can be use for field-work and nights or even hot and rainy days can be utilise for plotting.