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Posted on Aug 30, 2023 in Chemistry

Definition of Land Surveying

Surveying is the science that deals with the surveying in the field of relative positions and heights as well as the size and shape of any part of the earth surface including all detail and the projection of the measured data or detail on a map against a suitable size or scale. Surveying may also include determining relative heights of different points on the earth’s surface. 


What is a map or plan?


A map is both a generalized as well as reduced presentation on a flat surface of a part of the curved surface of the earth. 


What are coordinates?

Coordinates is a system of magnitudes used to fix position of point, line or plane. 


For accurate leveling

Observation lines to points or the staff must not exceed 60m 


At a set-up all lines must be of equal length except where it is not possible with intermediate readings

Observation lines need to be more than one metre above the ground. Rays lower than one meter are subject to refraction cause by warmer air closer to the ground than higher up.

.Benchmarks can also be determined underneath roofs, against the soffit of bridges and columns etc by using the staff either straight up or up side down. These readings are theoretically negative readings.

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Certain methods that could be follow in the field to eliminate the error.

.          As seen, make a balanced set-up in the field between the two staves

.        If the surveyor knows the extend of the error, an error per meter can be calculated and then applied over the distance from the level to the staff.

.        Make a balanced set-up. First close to the one staff; take a back sight and fore sight readings. Determine the height difference. Move the instrument now close to the second staff. Again take back sight and fore sight readings. Calculate the height difference. Determine the mean between the two differences

·Writing the numbers on the staff down wrongly

·Exchanging the back sight and the fore sight columns

·Adding and subtracting errors

·The staff is not keeping in the same place for back sight and the fore sight readings

·Tubular bubble is level

·The level is not in an excellent adjustment

·The staff is not held up vertically

·The tripod and staff are not on stable ground

·Parallax error

What is a Traverse

A traverse is consecutive polars.  A traverse starts always at a known point and ends at a known point.  The starting point’s coordinates are known to us.  Thus a traverse consists therefore out of coordinates, directions and distances.

Purpose and Accuracy

·The purpose of a traverse is to provide the relevant survey of adequate control points. 

·Used for future surveys.

What is the significance difference between traversing and leveling taking in mind the staff and instrument positions?

In leveling the staff is on position where as the instrument is on position in traversing

Factors influencing the accuracy of traversing

·The accuracy of the instrument.  On engineering sites it is not always necessary to make use of single second instruments because the distances used are relatively short in comparison with triangulation surveys where distances could vary from short to tens of kilometers and where accuracy plays a major role.

·Experience of the surveyor.  The bigger the knowledge and the discipline of the study area and the skillful handling of the instrument the less chance there is for errors and blunders to occur.

·The accuracy of the start and end point of the traverse.  If they are high quality then the traverse could also be very accurate.

·The type of survey to be executed.  Monitoring of structures requires accuracy of very high standard- parts of millimeters, 0. 0001, while cadastral surveys require lesser accuracy of to the nearest half of a centimeter.  Detail surveys could be to the nearest 0. 1m. The accuracy is subject to the scale of the present plan.

Name the elements of doing and calculating a traverse

·Coordinates

·Directions

·Distances

Write down a condition of the adjustment of the level that makes it possible to eliminate the collimation error yourself

·The tubular bubble need to be perpendicular to the vertical axis of the instrument and

·the observation line need to be parallel to the axis of the tubular bubble

How would you determine in the field if the level has a collimation error

Name the corrections you would apply in the field:

·Scale and sea-level

·Slope

·Temperature

Four methods can be used to express scales on maps:


·Word scale: a word scale is a verbatim statement but is only convenient when using small scale maps.. Word scale maps are not as effective on large scale maps, e.g. an

·Ratio scale: In the case under discussion, the scale means the units must be the same, e.g. 1:1 250 or 1:500. That means the units must be the same on both sides of the ratio. 


·Fraction scale: In this case the ratio is expressed as a fraction, 1/1250 or 1/500. This is also known as a representative fraction scale (RF).

·Graph or line scale: The presentation of such a scale is the specific division on a straight line of a comfortable length in order to facilitate the easy reading of distances on it.

Contour lines: A contour line is a line that joins points of the same height together. It is therefore a visual representation of a map of a specific terrain as seen from above.

Contour interval: A contour interval is the perpendicular distance between two subsequent contours.

Characteristics of contours


·The angle of inclination influences the horizontal distance between contour lines


·Contours never cross one another

·Contour lines are always closed


·Contour lines must have height value.

·A contour index can also be used, which is a slightly thicker line as the other lines and spaced at regular intervals of contours.

·Conformity: That is when the scale of a map at any point of the map is the same in any direction on the map. That is when meridians (lines of longitude) and parallels (lines of latitude) cross each other perpendicular.


·Distance: A map that maintains distance reflects distances from the centre of the projection to any other part of the projection.

·Direction: Maintaining direction on a map is when angles reflect the same distortion or deviation from any point on a line to another point.

·Scale: Scale is the ratio between the distance on a map and the same distance on the ground.

·Area: Maintaining area on a map is when all the areas have the same ratio as the areas on the ground.

·Cylindrical Projections (Gauss Conformal Projection or Transversal Mercator Projection)


·Conical Projection


·Zenithal Projection
The projection system that is used in South Africa is the Transversal Mercator projection, also known as the Gauss Conformal projection.

·

·The land is divided in sections of two degrees longitude in width. The section where the work is going to be done must be indicated,

·The central meridian is always an uneven meridian of line of longitude (Lo 27°, Lo 29°) and projects as a straight line.


·The origin of each section is the cutting edge of the central meridian and the equator

·Distances are measured clockwise from the south, which is zero degrees (0°). The direction from A to B:AB=∝and the direction B to A:BA= ∝± 180°

·A perceived direction projects as a bent line, as the equal meridians.

Name the data types we can collect in surveying:

Surveying is the science that deals with the surveying in the field of relative positions and heights as well as the size and shape of any part of the earth surface including all detail and the projection of the measured data or detail on a map against a suitable size or scale. 


Name and write down the formula of the other corrections that you would know and will apply to correct a measure distance in the field