Faculty of Architecture, Planning and Surveying

QSD 146 - Land Surveying

Extra Assignment - Traverse

Name : Dahlia Binti Ab Aziz

Class : AP1141FC

Lecturer’s Name : En. Mohd Zaki

ORIGIN OF TRAVERSE Middle English, from Anglo-French traverser, from Late Latin transversare, from Latin transversus

First Known Use: 14th century

TRAVERSE (SURVEY)Traverse is a method in the field of surveying to establish control networks. It is alsoused in geodetic work. Traverse networks involved placing the survey stations along a line or path of travel, and then using the previously surveyed points as a base for observing the next point. Traverse networks have many advantages of other systems, including: Less reconnaissance and organization needed. While in other systems, which may require the survey to be performed along a rigid polygon shape, the traverse can change to any shape and thus can accommodate a great deal of different terrains. Only a few observations need to be taken at each station, whereas in other survey networks a great deal of angular and linear observations need to be made and considered. Traverse networks are free of the strength of figure considerations that happen in triangular systems. Scale error does not add up as the traverse as performed. Azimuth swing errors can also be reduced by increasing the distance between stations

The traverse is more accurate than triangulation and trilateration, and sometimes even triangulateration (Chrzanowski and Konecny, 1965; Adler and Schmutter, 1971

PROPOSE OF TRAVERSE

Control PointA traverse network of survey line and ground marks can be used for reference for other traversing work

Surveying DetailA traverse network of survey line and ground marks provides control points which can be accurately plotted in a map or plan.

Setting OutThe position of road, building or other new construction.Pegs can then be set out on the ground from the traverse to define the position of such new work.

The Length of each Traverse Line Traditionally, this was done by using a steel band and applying a series of corrections to allow for the sagging of the tape, temperature effects, and so on. Today it will be done electronically with the Surveyor using a highly sophisticated Total Station set of equipment that can measure both distances and angular measurements to a high level of accuracy.

The Bearing of each Line The bearing of a line is its orientation with respect to grid North. This may be found for an initial line by starting at a station with known coordinates and orienting the Total Station with respect to another point with known National Grid coordinates such as a church spire. The Surveyor will locate the Total Station accurately over each traverse station in turn and will measure the horizontal angles as indicated in figure 6 below. These measurements are to a high level of accuracy and several readings will be taken to minimise the possibilities of measurement errors. The angles are measured in degrees, minutes and seconds. (1 degree = 60 minutes; 1 minute = 60 seconds)

Control SurveysAll measurements taken for engineering surveys are based on a network of horizontal and vertical reference points called control points. These networks are used on site in the preparation of maps and plans, they are required for dimensional control (setting out) and are essential in deformation monitoring. Because all surveying needs control points at the start of any engineering or construction project a control survey must be carried out in which the positions of the control points are established. The positions of horizontal control are usually specified in rectangular (x and y) coordinates.

TYPES OF TRAVERSE

Open-Loop

The open-loop traverse begins at a control point, an intuitive quantity that changes depending on the independent variable, which is a finite length. All of the known control points seen within the traverse are called observations. The ending point of the open-looped traverse is similar to the starting point. Observations are forward and back to the points on the traverse's path. Observations do not go back to the end of the traverse, according to Autodesk University. When an open traverse is shown as a graphic, the traverse is a line with two ends that do not connect to each other at the ends, which is what is often called a line in geometry, according to ICM Survey Systems. Open traverses are usually used to plot out roads, driveways and garden paths.

Closed-Loop The location where the traverse begins is known as a closed traverse, according to Autodesk University.

For the traverse to end, the initial traverse point has to be observed. The surveyed reading that was taken backwards to the formerly observed location is horizontal and angular with the closed-loop traverse or is an observed existing point. When using the leapfrog method, a closed-loop traverse and redundant observations of distances and angles results. The leapfrog method is a mathematical way of figuring out an unknown function that communicates the numerical values of the intuitive idea of quantity. When depicted graphically, the closed traverse looks like what is called a shape in geometry, with the shape having no opening, according to ICM Survey Systems. Closed traverses are often used to mark boundaries such as with boundaries between two different properties or between the homeowner's property and the city or town's property.

Closed-Connected The coordinates in the closed-connected traverse are not changed by adjustments made to the traverse.

Errors made in the data collected through the process of surveying which effect the observation are reported in the traverse notes, according to Autodesk University. Then, the traverse is then adjusted so that the traverse arrives at the known coordinates. Closed-connected traverses are often used to expand a new traverse into an existing traverse, such as when a property is expanded.

Surveying by open-compass traverse (polyline)The product of an open compass traverse is always a polyline. The corners of the line may represent points whose positions it is wished to plot, or the polyline may describe the shape of a linear feature. In the example provided the polyline is taken to represent the centerline of a path.

Set a marker on the ground at Point A. From Point A take a compass bearing on Point B, then measure the distance between Point A and Point B. From Point B take a compass bearing on Point C, then measure the distance between Point B and Point C. Repeat for the remaining legs of the traverse.

Record the results of the survey in a data table similar to that shown above. The bearings shown in the table of survey data are grid bearings. (Magnetic compass bearings must be converted to grid bearings by compensation for local magnetic variation. If magnetic north is west of grid north in the area of survey the variation is deducted from the magnetic bearing. If the magnetic north is east of grid north the variation is added to the magnetic bearing).

Surveying by close-compass traverse (polyline) The procedure is very similar to the open-compass traverse but enforces the creation of a polygon. The CLOSE statement in the xy file forces to close the polygon. It is good practice to check the geometry of polygons by first plotting them without using the CLOSE statement. This will allow the magnitude of any surveying errors to be assessed. The product of a closed compass traverse is always a polygone. The corners of the polygon may represent points whose positions it is wished to plot, or the polygon may enclose a landscape feature (as it does in the example below). The magnitude of surveying errors may be assessed by plotting the polygon in Map Maker without using the CLOSE

statement in the XY file (see below).

Set a marker on the ground at Point A. From Point A take a compass bearing on Point B, then measure the distance between Point A and Point B. From Point B take a compass bearing on Point C, then measure the distance between Point B and Point C. Repeat for the remaining legs of the polygon, ending at the starting point.Record the results of the survey in a data table similar to that shown above. The bearings shown in the table of survey data are grid bearings. (Magnetic compass bearings must be converted to grid bearings by compensation for local magnetic variation. If magnetic north is west of grid north in the area of survey the variation is deducted from the magnetic bearing. If the magnetic north is east of grid north the variation is added to the magnetic bearing). Surveying by offsets (polyline or polygon):The product of a survey carried out by offsets is a polyline whose corner, A to M in the example, might represent points whose positions it is wished to plot or points on a linear feature. In this example the feature under survey, represented by a broken black line, might be thought of as the edge of a stream. Markers are placed at Station 1 and Station 2, and their positions are determined. The line connecting Station 1 and Station 2 is the baseline for the survey. Offsets are measured at intervals from the baseline to the feature under survey. The offsets must be at right-angles to the baseline. In the example, the first offset starts at a distance of 19.20 m from Station 1 and is 25.90 m long. The second offset starts at a distance of 34.90 m from Station 1 and 47.40 m long, and son on for the remaining offsets.

Record the results of the survey in a data table similar to that shown below.

In the example shown, when viewed from Station 1 looking towards Station 2 the baseline has been set out to the left of the feature being surveyed. When a baseline is set out to the right of a feature (when viewed from Station 1 looking towards Station 2) the lengths of the offsets must be entered into the xy file as negative numbers.Surveying by distances from fixed points (polyline or polygon):The product of a survey carried out by measing distances from two fixed points can be a polyline or a polygon. Map Maker will draw a polygon if the last coordinate in the xy file is the same as first one, as it is in the example. If the first and the last coordinates in the xy file are not identical a polyline will be drawn In the example the feature under survey is to the right of a line connecting Station 1 to Station 2, when viewed from Station 1. In cases where the feature under survey lies to the left of a line connecting Station 1 and Station 2, when viewed from Station 1, the distances measured must be entered into the xy file as negative numbers. Set out two markers on the ground, Station 1 and Station 2, at points of known position. Then measure the distance from each station to Point 1, Repeat for the remaining points and record the survey data in a table similar to the one shown.

Utilisation : Close travese is useful in marking the boundaries of wood or lakes . Open survey is utilised in plotting a strip of land which can then be used to plan a

route in road construction.

Latitude and Departure

Latitude and departure are uses for obtained the accuracy of traverse and determine the coordinate for each of traverse station.

Latitude is the different of distance on the north-south axis between two point survey. Departure is the different of distance on the east-west axis between two point survey.

Latitude = D cosineθ Departure = D sineθ

Traverse CalculationsTraverse calculations involve the calculation of the 1) whole circle bearings 2) the coordinate differences and 3) the coordinates of each control point. To illustrate these calculations we will use the traverse ABCEDFA below throughout

Calculation of Whole Circle BearingsTo calculate the coordinates of a control point the WCB must be known as we sawearlier. This is done according to the following formulae:

Forward bearing YZ = Back bearing YX + (for the above example)In general,

Forward bearing = back bearing + left hand angle

A forward bearing is a bearing in the direction of the traverse e.g. XY and YZ, a Back bearing is a bearing in the opposite direction to the traverse e.g. YX and ZY. Forward and back bearing differ by ±180°.

The left hand angle is the angle between the bearing lines at a control station that lies to the left of the station relative to the direction of the traverse, i.e. the internal angle for anticlockwise traverses and the external angle for clockwise traverses.

Example: WCB at station A of the ABCDEFA traverse

The calculation of WCBs must start with a known bearing or an assumed arbitrary bearing. Here the first bearing AF is known to be 70°00’ 00’’. Because the internal angles have been measured the traverse is calculated in an anticlockwise direction and AF is a back bearing.

Forward bearing AB = back bearing AF + adjusted left hand angle at A= 70°00’ 00’’ + 115°11’ 10’’ = 185°11’ 10’’ (WCB at A)

Calculation of Coordinate DifferencesExample: Traverse ABCDEFA, line AB + BC

Coordinate Differences : Bowditch Adjustment MethodFollowing calculation of ∆E, ∆N and the misclosure errors eE and eN an adjustment of those errors ∆E, ∆N must be made. This method is most suitable for traverses carried out using steel tapes Adjustment to ∆E (or ∆N) for a traverse line = ∆E (or ∆N) = - eE (or -eN) x length of traverse line / total length of traverse

Coordinate Differences : Equal Adjustment MethodThis adjustment method is most suited for traverses carried out with total stations

δE=− eEn δE=− eNnCalculation of CoordinatesRecalling from earlier that the coordinates of a point are calculated as follows forpoints B and C:EA, NA were given as 350.000mE, 500.000mNEB = EA ± ∆EAB = 350 – 7.768 = 342.232mENB = NA ± ∆NAB = 500 – 85.517 = 414.483mN

TRAVERSE

Before the 1950-1960 decade, use of combined distances and directions was restricted to small areas but later, with the development of EDM and EODM equipment, larger networks with longer sides (5, 10, 15, 20, ... km) could be created. As stated at the beginning of 2.2.2, these techniques superseded triangulation.

For some time (about 1960) a new technique based on exclusive side measurement (trilateration) was considered but it was quickly rejected, mainly due to a lack of internal checks. To clarify this concept, a single triangle has an angle closure condition while a trilateral of the same shape has no way of being checked; a quadrilateral with two diagonals and all its directions measured, has four closure conditions whilst the same trilateration geometrical figure with its 6 sides measured has only one verification. This advantage with triangulation is limited since the method requires some sides being measured (baseline); however, trilateration can be conducted without observing any angles.

A combination of both techniques resulted in a suitable solution, although sometimes termed triangulateration, here it will be termed traverse, although often a traverse may be a simple succession of measured angles and distances.

One of the most important properties of traverses is that error propagation is independent from configuration; that is there is no requirement for complex network design involving suitable geometries or erecting towers to facilitate certain lines of sight. From the practical point of view with this kind of network, uniformity of control points with survey stations or aid to navigation requirements was possible.

In general, it is advisable to maintain a reasonable balance between the accuracies of both types of measurements (directions and distances) in order to improve the geometry independence in relation to the accuracy of results. One of the applicable rules is

σDIST σANG DIST 200000

where σDIST is the distance standard deviation stated in the same unit as DIST, and σANG is the standard deviation of a measured direction stated in sexagesimal seconds. Then, for σANG = ± 1" the distances required are 5 ppm (1/200000) and for ± 4", 25 ppm (1/40000) is enough.

The required angular or distance errors must never be confused with the instrument reading or resolution capabilities. The observer limitations, the environmental conditions, the correction accuracies, the time when measurement were made, etc., must also be considered.

For example, for an inclined distance measurement with an angle of elevation of 20º and 5 km in length, with an elevation difference error of ± 0.5 m, the error in its horizontal projection is expected to be

0.5 m tan 20° = 0.18 m

Thus, in spite of being measured with EODM equipment, whose error may be in the order of ± 1 cm ± 2 ppm, and with the inclined distance error of ± 2 cm, if used for transferring a horizontal position, the error is ± 18 cm.

A distance measured with EDM equipment must be corrected for environmental conditions (pressure, temperature, humidity).

Humidity is calculated according to pressure and temperature with dry and wet bulb observations, it is very important for measurements taken by microwaves. No measurement should be taken with EDM in an oversaturated atmosphere (rain, drizzle, fog); with EODM measurements humidity is not so important, although the luminous wavelength used should be considered. LASER radiations have an advantage since they are basically monochromatic, it is generally sufficient to obtain pressure and temperature data. For long distances (more than 5 km) it is recommended that the environmental parameters at both ends of the distances to be measured are obtained and then averaged.

Manufacturers usually provide the instructions for making the necessary corrections to their equipment. In EODM, the reflector prisms should be used with the equipment with which a calibration was conducted to avoid errors in measured distances, sometimes above 1 cm.

In distances above 5 km corrections for earth and ray curvature must be made. Such correction is:

1 − k 2 D324R²

Where k is the refraction coefficient (rate between earth and ray radius). In mean conditions it is 0.25 for microwaves and 0.13 for luminous waves. It is sufficient to introduce its approximate mean value as earth radius.

R = 6371000m

Figure 6.5 illustrates D (measured distance) and S (reduced distance to reference surface) meanings. This is necessary for the above correction and the correction for point elevations, which is detailed below.

Fig. 6.5

It is important to note that the above correction for curvatures takes into account the geometric effect of both arcs as well as the physical influence produced as a consequence of ray propagation at a slightly lower level than that for mean environmental conditions at both ends.

Correction for ray elevation and inclination is more significant. The general expression is:

S D² −(H2 − H1)2

(1 H1 )(1 H2 )

R RThe way in which such elevations are obtained, especially their difference H = (H2 - H1), affect the correction error. By simply considering the numerator:

S ≈ D² − H ²

we can deduce the influence:

dS ≈h

d h id HD² − H ²

previously mentioned. Therefore, the elevation difference error must be multiplied by the slope, i = tan α, in order to obtain the influence produced on the corrected distance error

In topographic surveys it is usual to make calculations in plane co-ordinates; for this purpose it is necessary to have previously applied corrections to the projection plane. The way in which this type of corrections may be calculated is detailed in 2.2.5.

The general and most correct way of calculating a traverse network on the representation plane is via a previous calculation of the co-ordinates for every new point commencing with the values of the known points and the uncorrected observations. It is necessary to average some results taken from different points starting with the additional redundant observations. When the provisional co-ordinates have been accepted, the above corrections should be applied and then observation equations are to be obtained, the unknown quantities of which are the corrections to the co-ordinates, in order to conduct a least squares adjustment.

If any observation exceeds tolerance levels (maximum admissible error) the original records should be checked, if no apparent cause is found regarding the error source re-measurement should be considered. If there is sufficient redundancy, the erroneous observation may be removed and a new adjustment conducted.

In some basic traverse circuits an approximate adjustment may be achieved by distributing the angle closure error first and then the co-ordinate closure error proportional to side length or some other logical criteria.

Angle closure errors in traverses must be below:

5"2" n

where n is the number of angular stations making up the circuit. In secondary traverses, intended to increase the density of the control points, the error may extend to:

(10"10" n)

When the purpose is limited to fixing co-ordinates of coastal details, larger tolerances may be permitted.

Co-ordinates closure errors should be no more than the values stated in Table 1 depending on the use of the network, noting that adjusted co -ordinates for intermediate points will have errors in the order of half the closure error. Nevertheless, for control networks, closure errors should not be greater then ±(0.2 m + 10 ppm) for primary horizontal control and ±(0.5 m + 100ppm) for secondary stations to meet the requirements in 2.1.2.

When errors are greater than a traverse tolerance, there are methods available to assist in locating the error source. For example, when an angle closure error is detected the grid bearing of the suspect side is calculated from all components of the co-ordinate closure error. However, if there is a large angle error, the angles should not be adjusted, on calculating the traverse in both directions, only at the affected point will the co-ordinate values roughly match.

When a network is accurately adjusted by least squares from provisional co-ordinates, the process enables, from the variance-covariance matrix, the calculation of adjusted co-ordinate errors. A similar calculation in a traverse may not be so clear since co-ordinate closure errors are more general. In such cases, the mid points may be permitted to have an error in the order of half the closure error, decreasing towards each end.

Traverse calculations in plane co-ordinates are very simple. The initial grid bearing is obtained from increases in E, N. Two control points whose co-ordinates are known in advance are represented as P

and Q in Fig. 6. Then:

tg B EQ − EP

EPQ

PQ

NQ − NPNPQ

where EPQ and NPQ signs (+/-) also define the quadrant.

If true azimuth referred to true north, rather than grid north as the referred available orientation, with grid declination γ (the definition of which is given in Annex A), this be should be taken into account. From this point forward only plane orientations (grid bearing) will be considered. Moreover, if a Transverse Mercator projection is used, it is assumed that corrections to observations (distances and directions) for the plane of representation have been made according to specifications in 2.2.5.

Fig. 6.6

Returning to computing a traverse, the grid azimuth of the first side is obtained by simply adding the first angle:

BP1 BPQ α0

B12 BPQ α1 180

And using the following general form of bearing transfer:The sign + is used in case the previous addition (BP1 + α1) is below 180º and the sign - when it is above. The latter is the most common case.

Increases in co-ordinates are obtained with the expressions for converting polar co-ordinates into plane co-ordinates:

N S cos BE S sin B

It should be remembered that, in the cases of simple traverses, before making such conversions, it is normal to adjust an angle by distributing the closure error if it is below the given tolerance level. In more complex traverses, network calculations may be supplemented with the algorithms related to intersections or resections according to descriptions in 2.2.4 and 2.2.5. Adjustment requirements mentioned above should also be considered.

As regards adjustments, their respective methods will not be developed further, since such processes are expected to be developed at the NHO where appropriate software is available. It should be remembered, however, that good results may be achieved only if the data is checked in the field to ensure that closure errors or the calculation of point co-ordinates carried out by different methods show an acceptable consistency with the above specifications.

A simple traverse is deemed to be fully closed if it starts from a pair of control points and ends at another pair. There are then three possible closure errors available: one angle closure error and two co-ordinates closure errors. This case is illustrated at the top of Fig. 6.7; it allows an initial angular adjustment and a subsequent distribution of the differences in co-ordinates. There is a special case of a simple closed traverse which makes a circuit, starting and ending at the same point. Even though it may be properly checked as detailed above, it is not advisable to conduct such methods for the reasons set out in 2.1.5

A simple traverse is termed half closed when a direction to another control point has not been measured from the final point; this means that no known angle checking or its corresponding adjustment is permissible. Nevertheless, if co-ordinate closure errors are acceptable, a similar distribution as in the previous case may be carried out as illustrated in the second case of Fig. 6.7.

A simple traverse is deemed to be precariously closed when, although it starts and ends at control points, there is no final measured direction with an orientation. The only check is to confirm that the measured distance between the control points P and R generated from the traverse is fairly consistent with the distance calculated from their known co-ordinates; this illustrated in the third case in Fig. 6.7. The simplest way of calculating the distance is by giving it an arbitrary or approximate orientation for the initial calculation and by then rotating the orientation and adjusting the length according to the differences to the end point.

Fig. 6.7

A simple traverse is deemed to be an open, not closed, or hanging traverse only if it starts from known points but ends at new unknown marks, thus no closure verification or adjustment can be made; this is not a recommended configuration. When it is the only choice, extreme caution should be exercised and the temporary nature of subsequent results should be clearly stated.

Traverses are closely associated with trigonometric levelling operations. These consist of a series of measurements taken to determine differences in elevations by vertical angles. (See 4.2 at Chapter 2)

The most precise way of obtaining a trigonometric difference of elevation consists in measuring the direct distance between the points and the vertical angles reciprocally and simultaneously from both stations:

i s i2

s2

α − α

H12 1 1

− D sin 1 22 2 2

where (see Fig. 6.8):

i1 = theodolite height above bench mark in point 1;s1 = signal (target) height above bench mark in point 1;

i2, s2

= theodolite and signal heights above bench mark in point 2;

D = slant and elevated distance (see Fig. 6.5);H12 = difference of elevations between benchmarks 1 and 2.

The elevation angles (α) are positive when they are above the horizon and they are negative when below the horizon. In Fig. 6.8 α1 is the positive angle and α2 is the negative angle. It is necessary for both to be simultaneously measured in order for a correct adjustment of ray curvature, which changes throughout the day.

A trigonometric difference of elevation obtained under these conditions may have an error of

± 0.01 m · K

where K is the distance expressed in kilometres, which is an error of 1 cm/Km.

If slant distance (D) has not been measured and ground distance reduced to the reference level, commonly the mean sea level, is available, which is the case of triangulation or intersection (see Fig. 5), the formula to be applied is:

i s i s2

Hm α − α

H12 1 1

−2

S 1 tg 1 2

2 R2 2

Fig. 6.7

If the elevation angle is known only at point 1, the formulae to be applied are:

H12 i1 − s2 D sinα1 (12−

Rk) D²

H12 i1 − s2 S 1 HmR tgα1 1

2−

Rk S ²

In the last three formulae, R is the terrestrial mean radius, in principle 6371 Km, but a more correct value relative to latitude and azimuth may be used for the adopted spheroid. The same is valid for the formula above to transfer D to S (See Fig.6.5)

S D² − H ²

H H

1 1 1 2R R

Hm H1 H22

Hm is the mean elevation

If only H1 is available, it may be calculated as:

Hm H1 H12

2

Where H12 is obtained by an iterative process which improves the value H2.

Coefficient k has the above stated meaning and it can be considered to have a value of:

k = 0.13 ± 0.05

then the error of a non-reciprocal trigonometric difference of elevation may be:

± (0.01 m K + 0.004 m K²)

The use of trigonometric levelling is ideal both for reducing the sides due to differences of elevations and height and for other altimetric requirements to overcome possible accuracies.

ERRORS

Even with the most accurate of angular and distance measurements in any traverse over a long distance errors will creep in. Large errors are not acceptable but making small adjustments in the calculations can compensate for small errors. This will not be covered in any detail here but it should be noted that in a closed traverse, such as shown in figure 5(a), a simple accuracy check can be applied by noting that geometrically the sum of all the internal angles must equal [(2n-4)x90o] where n is the number of sides of the traverse. Also, if the traverse closes back on itself the sum of all the calculated Differences Easting must sum to zero and the sum of all the Differences Northing must sum to zero (taking account of the signs of these calculated values). Similar but different checks can be applied to unclosed traverses where they can be tied in to points of known coordinates.

Adjusting For Closure Error

Horizontal angles In a closed polygon, the sum of the interior angles = 180o (n-2), where n is the number of sides in the polygon,

thus the sum of the horizontal angles in a triangle (n = 3) is 180o; an equal angle is subtracted or added to each measurement to satisfy the equation for interior angles; if the closure error is not equally divisible by n, make the largest adjustments to the largest angles.

The sum of deflection angles for any closed polygon is always 360o; this provides for another means of determining and adjusting for closure error.

Difference in elevationClosure error can be determined for closed and closed-loop traverses. The closure error can be divided by the

number of stations on the traverse or the correction at each station can be calculated according to the distance from the origin of the survey:

Ci = di/L * Ec, where Ci = the correction applied to station I di = the distance to station i from the origin of the traverse L = the total length of the traverse Ec = the closure error

This method accounts for the propagation of error with distance.

Horizontal distancesAs with leveling, closure error can be determined for closed and closed-loop traverses, where the coordinates of

the end points are identical or known. Location in the horizontal plane are given by x and y coordinates (e.g. northing and easting). Using the measured horizontal distances and adjusted angles, calculate the coordinates of each station. The difference between the calculated and known coordinates of the end control point is dx and dy, the closure error in x and y. As with leveling, the adjustment is a function of the distance traversed (Li) relative to the total length of the traverse (L):

Cdxi = dx * Li/L Cdyi = dy * Lii/L, where Cdxi and Cdyi are the adjustments in x and y coordinates at station i

The relative accuracy of distance measurements can be expressed as ((dx2 + dy2)1/2)/L. An angular error of one minute is equivalent to a distance measurement error of 3 cm over a distance of 100 m, since the sine of 1/60o is .00029.PROCEDURE IN SURVEY WORK

Reconnaissance SurveyCarried out to determine and selection of suitable station points. The criteria for selection of station points:- Use “whole to part “ principle. The number of station must be minimize but cover all the survey site.

The distance between station must be far (more than 30 m) and same as other traverse line. Avoid the sight line to close with earth surface. Station must be at the stable surface. Try to avoid any disturbance such as tree, building etc. The station must be available to observe all the detail surrounding.

Station Marking

The station can be mark when the station criteria had been full fill. The common station marking are wood peg and nails.

The selection of the station marking depend on the site condition. The survey works on the road, the suitable marking is nails. If the survey works in the forest or construction site, the wood peg is the best used as station marking. For permanent marking, the station can be in concrete.

Observation Checking 1. Total internal and external angle

Σ (Internal Angle) = [2n-4] 90º Σ (external Angle) = [2n+4] 90º

n = total number of stations.

2. Bearing comparison The last bearing is compare with the establish or known bearing value.

Example:Line AB read as 29º 29’ 21”Suppose read as 29º 29’ 29”Angle misclosure – 8” in 4 station a, b, c and d.Adjustment +2” per station.

3. Cross-bearing The checking was done by observation to the other reference station and compare the diffrence

CONCLUSION

In establishing the line of a new highway the engineering surveyor will initially establish a control network which is the framework of survey points or ‘stations’ for which the co-ordinates are precisely determined. The points are considered definitive and subsequent survey work, such as then establishing chainage points along the road centre-line, are related to them.

Physically, these stations will consist of, for example, short nails embedded in a road surface or nails cast into concrete-filled steel tubes driven into the ground. In all cases the stations must be rigid and not prone to disturbance or

movement. Their exact location will depend on the purpose of establishing the network and, in the case of a major highway, bends in the road and the need to be able to sight between stations may dictate the pattern of stations.

Care needs to be taken over the provision of control so that it is precise, reliable and complete as it will be needed for all related and dependant survey work. Other survey works that may use the control will usually be less precise but of greater quantity. Without an accurate control network it would be impossible to ensure the correct alignment of the highway or the accurate positioning of ancillary works such as service stations and junctions with other roads.

Apart from the specific example indicated in this exercise, other examples include setting-out for earthworks on a construction site, detail surveys of a green field site or of an as-built development and monitoring many points on a structure suspected of undergoing deformation.

The practice of using a control framework as a basis for further survey operations is often called ‘working from the whole to the part’. If it becomes necessary to work outside the control framework then it must be extended to cover the increased area of operations. Failure to do so will degrade the accuracy of later survey work even if the quality of survey observations is maintained.

Traversing is one of the simplest and most popular methods of establishing control networks for all types of major projects. In underground mining it is the only method of control applicable because of the linear nature of tunnels whilst in general civil engineering it lends itself ideally to control surveys where only a few points surrounding the site are required. Traverse networks have the advantages that little reconnaissance is required so planning the task is simple.