Most Common Errors in Plane Table Surveying
In this article, we are going to discuss about some common errors in plane table surveying. The degree of precision to be attained in plane table surveying depends upon the character of the survey, the quality of the instrument, the orientation of the instrument, the system adopted and upon the degree to which accuracy is deliberately sacrificed for speed. The various sources of errors in plane table surveying may be classified as
2.Errors due to plotting
3.Errors due to manipulation and sighting
a) Non-horizontality of board
The effect of non-horizontality of the board is more severe when the difference in elevation between the points sighted is more
b) Defective sighting
The accuracy of a plane table mapping depends largely upon the precision with which points are sighted. The plain alidade with open sight is much inferior to the telescopic alidade in the definition of the line of sight.
c) Defective orientation
Orientation done with a compass is unreliable, as there is every possibility of a local attraction. Erroneous orientation contributes to the distortion of the survey. The orientation should be checked at as many stations as possible by sighting distant prominent objects already plotted.
d) Movement of the board between sights
Due to the carelessness of the observer, the table may be disturbed between any two sights resulting in the disturbance orientation. To reduce the possibility of such movement, the clamp should be firmly applied. It is always advisable to check the orientation at the end of the observation from a station.
e) Inaccurate centring
It is very essential to have a proper conception of the extent of error introduced by inaccurate centring, as it avoids unnecessary waste of time in setting up the table by repeated trials.
These are the most common Errors in Plane Table Surveying. Hope you like this article.