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How to Draw Contours using Judgement and Free Hand Method
There are other method of contouring like the arithmetic estimation, but for less accurate but quick draw, one can use their fine judgement and free hand technique to draw the contours for the given elevation points.
In the following example, the control points are already drawn. The square patterned control points' elevations are shown, one has to use the fine judgement to draw the contour lines. See how it is done, all you have to do is to judge the contour line's placement from the given elevations.
Look at the nearest control point elevations. If the nearby elevation is higher, then the terrain is rising towards it, if it is lower, terrain must have a downward gradient.
Definitely the higher contour must lie towards the rising terrain and a contour with the lower elevation must lie towards the downward gradient.
Drawing Contour Lines free hand with fine judgement
Tacheometry is the branch of Surveying in which we determine the horizontal and vertical distances with the angular measurements with an instrument , Tachemometer. It is not so accurate method of finding the horizontal distances as the Chaining is, but it is most suitable for carrying out the surveys to find the distances in the hilly area where other methods are quite difficult being carried out. It is generally used to locate contours, hydrographic surveys and laying out routes of highways, railways etc.
The instruments required for carrying out the Tacheometric survey are: (1) A Tacheometer (2) A Stadia Rod. Tacheometer: Tacheometer is more or less a Theodolite installed with a stadia diaphragm. Stadia diaphragm is equiped with three horizontal hairs and one vertical hair. So we can take three vertical staff reading at the same instruments setting, lower most hair reading, central hair reading and the top hair reading. The difference between the lower hair reading and the upper ha…
A short introduction to plane tabling- A graphical method of Surveying.
Plane Table Survey: Plane Table Survey is a method of Surveying in which field work and the office work are done simultaneously. It is also known as the graphical method of Surveying. A manuscript map is made in the field and the topographic details can be filled in later.
List of Instruments used in Surveying:
(1) Plane Table(2) Alidade(3) Plumbing fork and Plumb bob(4) Spirit Level(5) Chain or Tape(6) Rain roof cover for the plane table(7) Compass(8) Ranging Rods(9) Drawing Sheets(10) Drawing equipment.
Procedure: To do the plane tabling one has to follow the following procedure at every plane table set-up: (a) Fixing the plane table to the tripod stand(b)Setting up and temporary adjustments:
Leveling the plane table with the help of spirit level Centering with the help of plumbing fork Orientation by trough compass or by back sighting
Trigonometric Leveling is the branch of Surveying in which we find out the vertical distance between two points by taking the vertical angular observations and the known distances. The known distances are either assumed to be horizontal or the geodetic lengths at the mean sea level(MSL). The distances are measured directly(as in the plane surveying) or they are computed as in the geodetic surveying.
The trigonometric Leveling can be done in two ways: (1) Observations taken for the height and distances (2) Geodetic Observations. In the first way, we can measure the horizontal distance between the given points if it is accessible. We take the observation of the vertical angles and then compute the distances using them. If the distances are large enough then we have to provide the correction for the curvature and refraction and that we provide to the linearly to the distances that we have computed. In the second way, i.e geodetic observations, the distances between the two points are g…