CURTIN UNIVERSITY DEPARTMENT OF SPATIAL SCIENCES PLANE AND CONSTRUCTION SURVEYING SPAT1001 Prac: Traversing and Mapping Exercise This practical runs on two parts and for four weeks PART I (Traversing): teaching weeks 8 and 9; PART II (Mapping): teaching weeks 10 to 12. PART I (Traversing) Objective To adjust a horizontal control traverse adjacent to the Edinburgh Oval. Description A six-sided traverse (7 points) has been set out and measured by a surveying group. You need to calculate and adjust the traverse to form the horizontal and vertical control network in the Edinburgh Lake. The plane coordinate system of MGA94 is to be used. Your traverse must be tied to at least two control points defined in this system. These two points are pillars number 17 and 18, which are located in Edinburgh oval, and their coordinates are: E N RL Pillar 17 395146.068 6458493.238 10.950 Pillar 18 395170.511 6458362.866 10.125 Your traverse will be formed as a closed-loop traverse from the two pillars 17 and 18 in addition to five selected stations. Fieldwork Description 1. A surveying group selected and marked five suitable traverse stations last year as shown in Figure 1. Each point is a nail at the centre of 20 cm stake driven in the ground with only a few mm visible above the ground surface. Care has been taken that all possible features of the area can be seen from the traverse stations. The stations are numbered 1-5 in a clockwise direction as shown in Figure 1. Plane & Construction Surveying 2 Figure 1: Work area and the control points (Pillars 17 and 18, and points 1 to 5). 2. The traverse started from pillar P18 (as the initial point). To establish the orientation of the traverse, the reference bearing has been obtained from the traverse leg P18-P17 since these two points have known E and N coordinates. 3. The locality sketch (description card) for all traverse points is available in the file Traverse_Survey Mark Summary.pdf. The locality sketch shows the location of each point tied by distance and bearing to three permanent features in its vicinity (e.g. trees, light poles, buildings, etc.). The distances and bearings to these features are written and drawn on the sketch. 4. The internal horizontal angles of the traverse at each traverse station are measured by closing the horizon method. Two arcs have been observed. Note that if mean values disagree by more than 20 of arc, the angles should be re-observed a third time. These angles are listed in the file Traverse_H-Angles and Distances Field Sheet.pdf. 5. The distances between all successive stations have been measured using the total station and recorded to the nearest millimetre. A scale factor (e.g. 0.999734) needs to be applied to reduce the measured distances to the map (this is called map projection, which will be further explained in other units. see also for some details the MGA94 computational manual on Blackboard). Note that during fieldwork, the correct prism offset, temperature and pressure should be used. The measured Traverse distances are written in the file Traverse_H-Angles and Distances Field Sheet.pdf. Plane & Construction Surveying 3 6. A levelling traverse has been run to determine the reduced levels (RL) of all traverse points defined in the AHD datum from the known RL of pillars P17 and P18, which are used as Benchmarks, starting from pillar P17 and closing at pillar P18. A levelling double-run (reciprocal) method was applied to detect errors. In the double-run method, we check the correctness of our measurements and that there is no outliers. For example, the level difference between two points (e.g. 1 and 2) is determined from 1 to 2 in one instrument setup and then revise and measure from 2 to 1 in a second setup. The difference in readings (R1-R2) in setup one and (R2 R1), which represent the difference in their RL, should be equal but with opposite signs. A difference within a few millimetres will be acceptable. To compute the levelling run, only the RL differences in one direction sequence should be used, i.e. 1-2, 2-3, 3-4, 4-5, etc. Additionally, in the main check of the fieldwork, we assume using the third-order levelling when closing the levelling loop, e.g. the misclose should be less than 12mmk, where k is the traverse length in km. The levelling records are written in the file Traverse_Leveling Sheet.pdf. Office Work 1. Compute the angular misclose for internal angles of the traverse. 2. Adjust the internal angles and compute the correct bearings of all traverse legs. 3. Calculate the linear misclose for the traverse. 4. Adjust the traverse using the Bowditch method. 5. Compute coordinates of all traverse stations and plot the traverse. 6. Compute the adjusted reduced levels of the traverse points. Submission This is an individual assignment and submission Results of Part I and Part II of this assignment should be submitted together in one report. Due Date: Friday 5 June 2020 Part I + Part II: 20% of the final mark. Part I 8% and Part II 12% The report should include for Part I: (a) Clear calculations of the angular and linear misclose, bearing swing and the table showing all calculations from the Bowditch Adjustment. The rate of linear misclose should not exceed 1 in 6000. (b) Computations for adjustment and coordinate reductions for the control traverse. You should use the traverse Table given in the lecture. (c) The plot of the traverse at an appropriate scale showing horizontal distances, bearings, legends and a table of adjusted coordinates. (d) A critical appraisal of the errors in the traverse.