UNAWEZA JIPATI NOTES ZETU KWA KUCHANGIA KIASI KIDOGO KABISA:PIGA SIMU:0787237719
The purpose of surveying includes the following:-
(i)To determine horizontal distance between points on the earth’s surface
(ii)To determine vertical distance or height between the points on the earth’s surface
(iii)To determine the area of the piece of land or plot
(iv) To determine the direction of various features on the earth’s surface
(v) To determine the location of physical and non-physical features on the earth’s surface Stages or procedures of conducting survey/surveying methods/surveying process
(1) Reconnaissance / preliminary inspection/primary surveying Is the process of taking general view of the land to be surveyed in order to get real picture of the work to be done. It is done by visual observation of the area. During the reconnaissance the surveyor does walking around the area to be surveyed and taking general views and noting down the dominant features area, Boundaries of the area, Corners of the boundaries of the area and Other structures such as building, big trees, ponds, lakes, small hills e.t.c Importance of reconnaissance
(i) It helps to get the full picture of the survey to be conducted
(ii) It helps for choosing the scale for map making
(iii) It makes survey for new coordinates and old coordinate easier
(iv) It shows the existing situation on a piece of paper
(2) Actual survey /secondary survey This steps involved observing, measuring and recording direction, angles distance and elevation by using surveying equipment or tools.
(3) Presentation this involves presentation of data or information collected or recorded, the information can be presented by writing or drawing form
BRANCHES /TYPES OF LAND SURVEYING
The following is the branches of survey.
METHODS/TECHNIQUES OF LAND SURVEYING
Depending on how linear and angular measurements are combined, there are four types of methods /elements/technique of land surveying. 1. Chain or tape survey 2. The prismatic compass survey 3. The plane table survey 4. The technique of levelling
Is the surveying method in which linear measurements of an area are taken Features of chain surveying
1. It is suitable for surveying flat surface on the Earth’s surface, for example a school compound
2. It can be red easily and quickly
3. It is the simplest method of surveying through the old method
4. It is suitable for surveying clear areas
5. It can be easily repaired or rectified in the field
6. It tends not to attract attention.
Disadvantages of chain survey
1. They become longer or shorter due to continuous use
2. It is not suitable for surveying large areas
3. More difficult areas cannot be chain surveyed
4. Errors may be encountered due to the use of many chains and other reasons
5. It is time consuming
6. They are heavy and take too much time to open or fold
7. It is a slow method of surveying
8. It is the oldest method of surveying
THE ERRORS THAT OCCUR IN CHAIN SURVEYING
An error is a mistake or shortcoming that happens during the survey process leading to wrong measurements. It is sometimes called discrepancies.
The following are the type of error or discrepancies in chain surveying.
Cumulative (systematic) Errors Cumulative errors are said to be systematic errors as they are one-directional hence keep on accumulating as the survey progresses. If not checked they have serious implications to the accuracy of the survey. Errors in this class included incorrect length of the tape, page of the tape or the tape not being in line. Since the sources of these errors are known, they can be eliminated. They can either be positive or negative errors. Positive errors shorten the measurement (e.g where the tape length is shorter that what it should be) while negative errors elongate the measurements (e.g. where the tape is longer what is should be). Errors can be eliminated by checking the equipment Compensating Errors (accidental) errors Compensating errors are said to be accidental errors hence cancel out and does not pose serious problem to the accuracy of the survey. They arise as are result of not being perfect in the use of the equipment or in the whole survey process. For example, if the pull exerted on the tape in either more than or less than what should be the case, faulty results be gotten. The effect can either be positive or negative Gross Errors These are mistakes that can be attributed to the inexperience of the leaders. These are very serious errors which although are random in accordance my lead to faulty plans and maps if not checked. They include discontinuing the chain length (e.g. where some arrows are cost or misplaced), misreading of the tape, reading tape upside down (e.g. taking 6 to be 9), etc. these errors can be corrected by taking the necessary precautions.
OVERCOMING OBSTACLES DURING CHAINING
Types of Obstacles
1. Visual obstacles: Is an obstacle that prevents an object but the chain remains free. An example of a visual obstacle is a forest.
2. Chain obstacles: This is the obstacle where by the chain is obstructed but visually it is free Examples are rivers and ponds
3. Neither visual nor chain obstacles for example buildings
HOW TO OVERCOME THOSE OBTACLES
1. By rectangular method
2. By triangle method
3. By using similar triangle method
By constructing rectangles Chaining had reached A and encountered an obstacle. To get to B, mark A and B with any arrow. Set of perpendiculars AC and BD high enough to clear the obstacles. Join and measure DC which now equals AB. This allows chaining to continue from B. By constructing similar triangles To continue chaining for B, fix point C away from the obstacle. Range a pole at D to align with Ac hence AC = CD. In line with BC range another point E in line with BC. Hence BC = CE Measure ED which equals AB hence chaining can continue from B. Obstacles which obstruct both ranging and chaining Chaining has reached B from A where an obstacle like a building has been reached. Erect equal perpendiculars AC and BD from A and B along the chain line. Along CD, range E and F beyond the obstacle. Set off perpendiculars EG and FH from E and F equal to AC. AS G and H are in line with AB, then CE equals AG. By constructing triangles Chaining had reached A and there is the need to overcome the obstacles created by the stream to really B. Set out a perpendicular AC and mark the midpoint E. Set out another perpendicular CD so that D, E and B are in a straight line. The 2 triangles created are congruent CD = AB which is the required length hence chaining can now proceeds from B.
IMPORTANCE OF SURVEY
The following includes the general importance of survey
(i) It helps in determine distance between various points on the ground
(ii) It helps to determine heights on the ground
(iii) It helps to determine angles on the ground
(iv) It helps in determine areas of plots of land
(v) It helps to take ground measurements for construction of various structure E.g roads, buildings e.t.c
(vi) Leveling survey helps to determine level of sloped ground
(vii) It helps to determine for sight intermediate and back sight of various points on the ground especial sloped land.
(viii) Survey is help in taking measurements to some areas where underground structure to be constructed E.g. pipe line, underground canal etc.
Leveling: Is the procedure by which the heights of the points on the Earth’s surface are determined.
1. A staff is plat at station one or base station. Then the sighting instrument is put in the direction of travel when a back sight is recorded.
2. The distance from base station to the instrument is measured.
3. The staff man moves along the direction of travel ahead of the sighting instrument (telephone). This will be station two where a fore sight is recorded.
4. The sighting instrument is moved along the direction of travel ahead of the staff man. A back sight is takes and recorded.
The procedure is repeated until all the leveling is done and recorded.
Use Fullness of Leveling
– It helps to determine the relative heights on land that can be used in contour mapping.
– Leveling can be used for determination of heights or elevation of the land surface such as hills, valleys, plans, etc.
– Housing foundation, the location of industrial sites, the route of communication and sites of building can be located and determine with the help of leveling.
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UNAWEZA JIPATI NOTES ZETU KWA KUCHANGIA KIASI KIDOGO KABISA:PIGA SIMU:0787237719