Intersection Method |
In intersection method of plane table surveying, the objects or points to be located are obtained at the point of intersection of radial lines drawn from two different stations.
Figure 34.2 Intersection method of plane table surveying Let us consider plane table stations Z and Y (Figure 34.2) from which details got plotted by method of intersection. In this, first the plane table is set over the station Z, clamped and its position is plotted on paper as z. If the position of the station is not already plotted, then the station Y is bisected and plotted by method of radiation. Now, with alidade pivoted at z, salient object points on the surface of earth such as 1, 2, 3 etc of a building, 4 a telephone pillar, 5 a tree etc around the plane table got bisected and radial lines are drawn showing their directions. The table is then shifted to the station Y and get it set and after orienting by backsighting to station Z get it clamped. With alidade pivoted at y, same objects i.e., 1, 2, 3, 4, 5 etc. get bisected and rays are drawn. The intersection of the respective rays provides the plotted positions of the respective details. The plotted positions of 1,2, 3 are then joined to represent the building corner. Telephone pillar and tree are represented by their conventional symbols. In this method, the plotting of plane table stations are to be carried out accurately. Checking is important and thus done by taking third sight from another station. The intersection method is suitable when distances of objects are large or cannot be measured properly. Thus, this method is preferred in small scale survey and for mountainous regions. |