contouring

The ease with which total stations produce horizontal distance vertical height and horizontal direction makes them ideal instruments for rapid and accurate contouring in virtually any type of terrain the data recorded may be transformed from direction. 

1-position and elevation

distance and elevation contouring of point to its position and elevation in terms of three-dimensional coordinates These thus comprise a digital terrain or ground model (DTM/DGM) from which the contours are interpolated and plotted the total station and a vertical rod that carries a single reflector are used to locate the ground points A careful reconnaissance of the area is necessary contouring in order to plan the survey and define the necessary ground points that are required to represent the characteristic shape of the terrain Break lines the tops and bottoms of hills or depressions the necessary features of water courses etc.

2-curvature and refraction

and enough points to permit accurate interpolation of contour lines at the interval required . comprise the field data .

As the observation distances are relatively short , curvature and refraction might be ignored , However in most total stations corrections for curvature and refraction might be ignored However in most total station corrections for curvature and refraction may be applied .

it can be seen that if the reduced level of point A (RLa) is known then the reduced level of ground point B is :

RLb  = RLa + hi + ∆ h - ht

3- height of the ground

When contouring the height of the reflector is set to the same height as the instrument , ie  ht  = hi  , and cancels out in the previous equation , Thus the height displayed by the insttrument is the height of the ground point above A :

RLb  =  RLa  +  ∆ h

in this way the reduced levels of all the ground points are rapidly acquired and all that is needed are their position contouring One method of carrying out the process is by radiation .

the instrument contouring is set up on a control point A , whose reduced level is known and sighted to a second control point (RO) the horizontal circle is set to the direction computed from the  coordinate of A and the RO . 

4- measured horizontal distance

 

The instrument is then turned through a chosen horizontal angle (∅) defining the direction of the first ray Terrain points along this ray are then located by measured horizontal distance and height difference This process is repeated along further rays until the area is covered contouring

unless a very experienced person is used to locate the ground points , there will obviously be a greater density of points near the instrument station . the method however is quite easy to organize in the field . the angle between Many ground - modelling software package interpolate and plot contours from strings of linked terrain points.

computer processing is aided if the ground points are located in continuous strings throughout the area , approximately following the line of the contour , they may also follow the line of existing watercourse , roads , hedges , kerbs , etc , 

5- determined by linear

Depending on the software package used , the string points may be transformed into a triangular or gridded structure Heights can then be determined by linear interpolation and the terrain represented by simple planar triangular facets Alternatively  high -order polynomials may be used to define three-dimensional surfaces fitted to the terrain points from these data contours are interpolated amd a contour model of the terrain produced .