In surveying, contouring is the process of determining the elevation of distinct places on the ground and placing them in the same horizontal position on a contour map. Vertical control levelling work is being done while a horizontal control chain survey, compass survey, or plane table survey is being done at the same time. When using the theodolite, both horizontal and vertical controls can be accomplished with one instrument. Contouring can be classified into numerous groups depending on the equipment utilised. Contour Surveying Techniques Contour surveying can be done in two ways: Using the direct way Method of indirection.
In surveying, what is contouring?
It entails determining the vertical and horizontal controls of the points on the chosen contour line .A levelling instrument is widely used for vertical control. After taking fly levels from a nearby bench mark, a level is set on a commanding location in the region. The collimation plane/instrument height is determined, and the needed staff reading for a contour line is calculated. The instrument operator instructs the staff operator to roam about the area until the required staff reading is found. Using his instruments, a surveyor establishes horizontal control of that location. After that, the instrument man guides the staff man to another location where he can find the identical staff reading. It is adhered to.
As a result, multiple points are established on one or two contour lines and appropriately noted down. For this project, a plane table survey is perfect. The instrument is relocated to another point to cover greater area when the appropriate points are established from the instrument setting. It is not necessary to change the level and survey instrument at the same time. It is preferable if both are in close proximity so that they can communicate easily. Hand levels and Abney levels are sometimes utilised to speed up the levelling process. This procedure is time-consuming and tedious, but it is accurate. It’s ideal for tiny spaces. Contouring by Indirect Method Levels are taken at a few specified spots and their levels are decreased using this procedure. As a result, horizontal control is used in this strategy.
Method of Squares
The standard square dimension ranges from 5 m x 5 m to 20 m x 20 m. Levels of all grid points are established through levelling. After that, a grid square is drawn on the drawing sheet. Interpolation is used to draw contour lines and reduced levels of grid points. Cross-Section Methodology This method involves taking cross-sectional points at regular intervals. All of those points are established by levelling the reduced level. On the drawing sheets, the points are marked, their reduced levels (RL) are noted, and contour lines are interpolated. depicts a typical task planning process. The cross-section spacing is determined by the type of the terrain, the map’s size, and the contour interval necessary.
The mechanical or graphical method of interpolation involves utilising a tracing sheet to linearly interpolate contour points: Several parallel lines are drawn at regular intervals on a tracing sheet. To make counting easier, every tenth or fifth line is darkened. If A’s RL is 97.4 and B’s is 99.2 m, then Assume that the bottom darkest line represents 97 m RL and that each parallel line is spaced at 0.2 m intervals. Then, on A, keep the second parallel line in place. Rotate the tracing sheet so that point B is intersected by the parallel line 100.2. The points on the 98 m and 99 m contours are represented by the intersection of dark lines on AB. Similarly, the contour points of any line connecting two places may be different.
Contour Maps and Its Uses
Smooth contour lines are generated after identifying contour points and linking corresponding points on a contour line. Smooth lines can be drawn using French curves. A surveyor should not lose sight of the ground’s distinguishing feature. Every fifth contour line has been thickened to make it easier to read. Every contour line has its elevation indicated on it. If the map is particularly large, it is also written at the ends. Contour Maps and Their Applications Contour lines are imaginary lines that connect places of equal elevation on a contour map. After defining lowered levels of numerous points in the area, such lines are drawn on the plan of the area. The contour lines in a given area are drawn with the difference in elevation between them in mind.
The following are the properties of contour maps:Contour lines must close, but not necessarily within the plan’s boundaries. A flat surface is shown by a contour that is widely separated. The close spacing of the contours implies that the land is steep. A consistent slope is indicated by an evenly spaced contour. Uneven surfaces are indicated by irregular outlines. A pond is shown by approximately concentric closed contours with diminishing values towards the centre. Hills are shown by approximately circular closed contours with rising values towards the centre. Ridge is indicated by contour lines with a U-shape and convexity towards the lower land. U-shaped contour lines with convexity 2V-shaped contour lines with convexity. Valleys are indicated by contour lines that are V-shaped with convexity toward higher ground. Contour lines rarely cross or intersect one another. If there are contour lines,
Contour Maps and Their Applications
Contour maps are particularly valuable for a variety of engineering projects, including: To identify, a civil engineer analyses the contours and determines the type of the ground. A suitable location for the project’s work to be carried out. It is feasible to determine the profile of the ground along that line by sketching the section in the plan. If the formation level of the road/railway is determined, it aids in determining the depth of cutting and filling. Drawing a profile of the ground along a line can be used to determine the intervisibility of any two points. The railway, road, canal, and sewer lines’ paths can be chosen to reduce and balance earthworks. At any point in time, the catchment area and thus the quantity of water flow.
In surveying, contouring is the process of determining the elevation of numerous places on the ground and plotting these points in the same horizontal position on a contour map. A contour is an outline of a mass of land in the world of land property. The main goal of contour surveys is to find any significant differences in elevation on the existing land. A contour map in land surveying is a map featuring contour lines, such as a topographic map, that displays valleys and hills, as well as the steepness or gentleness of slopes. Find out more. Contouring’s Objectives A contour map is extremely useful since it provides important information about the terrain. A contour survey is conducted at the commencement of any engineering project, such as a road construction project.
Direct Method of Contouring
The contours to be located are immediately traced out in the ground using this procedure, which involves locating and making a number of points on each contour. The contours are then traced through these spots, which are then surveyed and plotted on a plan. The most accurate way of contouring is direct, but it is also the slowest and most tiresome because time is wasted searching for points of the same height for a contour. The Direct Method of Contouring is ideal for small areas requiring extreme precision. Contouring by Indirect Method Levels are taken at some selected sites and their levels are decreased in the indirect method of contouring. This strategy establishes horizontal control first, followed by the levels of those locations discovered.
In cartography, a contour line (often just called a “contour”) joins points of equal elevation (height) above a given level, such as mean sea level.
Direct Method of Contouring : High degree of precision is required for large-scale maps with small contour interval.
In the most basic terms, a contour survey illustrates the elevation differences across your land.
Also Check
Error Sources in Total Station in Surveying