International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Vol...
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Experience on using total station surveying for mapping and contouring

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Experience on using total station surveying for mapping and contouring

  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 155 EXPERIENCE ON USING TOTAL STATION SURVEYING FOR MAPPING AND CONTOURING RASHEED SALEEM ABED Remote sensing Center, University of Mosul, Iraq ABSTRACT Total station is a valuable source of surveying data. Yet, in large prpjects, its usage can be cumbersome, slow and prone to errors unless well designed procedures are followed. This paper documents the experience gained while doing planimetric and contour surveying using total station with reflectors. The management of field and respective office work to obtain easy, quick and more accurate results is described. Special concern is given to places of limited access and safety issues. The order to perform various tasks is important. Nomination of target points, creating data files, and the way various aspects of data collection, feeding, and processing treated is explained with the example of a major surveying work performed at the main campus of the university of Mosul. Keywords: Total Station, Surveying, Error Reduction, Contouring. I. INTRODUCTION The main campus of the university of Mosul (Iraq) located in the north eastern part of the city extends over an area of 1.5 km X 2.5 km. There are various degrees of irregularity in topography including flat, hilly and steep slope areas. It contains spots of water ponds, drains, marshes, canopy, open spaces, dense and scattered buildings and network of roads. During the past few years, the campus have seen major developments which came in two aspects. First, additional large open area have been added northwise to the main campus presently known as the college of agriculture. The second face of development is the major expansion in construction activities of new buildings, roads and services which are going on at various parts of the university area including the old site. The new open areas lack much of detailed and accurate planimetric and elevation maps. Moreover, even in the available old campus maps, errors in locations have been noticed at many places which amounts to tens of meters in horizontal extents.(Figure 1). Accurate heights are also not available. INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), pp. 155-167 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2013): 5.3277 (Calculated by GISI) www.jifactor.com IJCIET © IAEME
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 156 Fig. 1. An old university map with location errors mainly in the north portion These types of errors have caused much disturbance during the design and setting out of new projects. Sometimes, it was necessary to perform detailed re-surveying of a particular area for accurate setting out of a new building due to lack of accuracy. There was a great need to update the existing location data and elevation maps to cope with the new developments. Under the directions of the university authority, the author have undertaken a major surveying work which extends over a year period. First, it began with partial work which was extended later to include the whole area. The aim was to map the layout of existing constructions and adding/ updating the height information in the form of contouring. There are many techniques that can be used for planimetric and contour surveying suitable for this kind of mapping. Their usage is governed by the available instruments and manpower resources, these include field leveling and taping, photogrammetric methods, tacheometry, GPS and total station surveying etc [1]-[12]. However, in this work, it was decided to perform total station surveying for the following reasons. 1- Speed of work, high data storage and easier field and computer use. 2- High accuracy in distance measurements suitable for better planimetric mapping. 3- Suitability for height mapping (with caution [5]). 4- Evaluation of this instrument as it is being used recently for the first time in our laboratory. Generally, a total station resembles a collection of the following sub items [3],[8],[7]; • EDM • Electronic theodolite • On-Board Micro-processor • Data Collector (built in or separate unit) • Data Storage (internal or memory card) • A prisms attached to the rod is required at the other end of the measured line. (non- prism is also possible with some models [3],[8]) Total stations record various measured data as horizontal, vertical angles, and slope distances. It can derive horizontal distances and calculate three dimensional coordinates of the target prism point. There are a dozen of other derived products that may differ according to the manufacturer. Thousands of points can be saved in the internal memory for later
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 157 computer downloading. The speed of field data collection can be as high as (700 to 1000 points per day )according to manpower and field conditions, [3]. Many types of total stations can reach accuracy level of ± (2mm + 2 ppm) in distance measurements. But in vertical measurements and difference in levels, results are less accurate than those obtained using ordinary levelling[5]. This error in elevation is generally more at longer distances and depends much on the atmospheric turbulence in temperature, humidity and air pressure. Total stations inherit errors from using the theodolite and the EDM. They use methods of trigonometric leveling in height calculations. In our local conditions, the speed of field work is critical issue. Apart from the higher cost caused by delayed work, the hot season may give very limited suitable periods of doing the work. Moreover, in our case, security and safety issues are critical and have to be resolved in quicker work. In field surveying work the main focus is to collect points at various desired locations. Field notes provided by the surveyor will help later office work in producing the plans. Many references in total station surveying suggest the use of a dictionary of symbols that accompany the attribute data attached to each surveyed point. At office work, coded points can be drawn by the drafting software to resemble surveyed features. An example of label codes used for point identification can be seen in Table (1) [3],[4],[13]. TABLE I SAMPLE CODES USED FOR POINT IDENTIFICATION DURING FIELD SURVEYING Coding number Description Survey point 01 02 03 … 15 20 ….etc BM CM SIB … CL EP Bench mark Concrete Monument Standard Iron Bar … Centerline Edge of pavement The suitable symbol is usually fed to the instrument during collecting field data according to the type of the surveyed point. This process delays the surveying work while selecting the appropriate symbol at each ground location. Feeding the right symbol using the small compact keyboard interface of the total station is not quick task. Each letter can be reached after a sequence of few strokes. At the same time, on the other side of the surveyed line the prism holder has to collect different kinds of points at a given location before moving to a new place. It will be difficult in general to document all symbols of different field points at a reasonable speed. This will considerably increase the time of field work and may cause mistakes during data input. To overcome many of these difficulties and increase speed, safety and accuracy of the work, the author has utilized a systematic method of surveying planimetric and elevation details using total station. During the course of field and office work of this study, there was continuous modification to increase productivity and reduce errors. The remaining sections of this paper describe this methodology.
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 158 II. MATERIALS USED The following instruments were used during the course of this work. 1- Total station "TOPCON 235N" with reflectors [13]. This instrument is widely used low cost, performs major tasks. It calculates coordinates of target points in the form of "Easting, Northing, Elevation or E, N,Z". Thousands of points can be stored in the internal memory of the instrument and can be exported later to the computer for further processing. This instrument can measure a distance up to 3000 m using a single prism. The reported distance accuracy of this model is ±(2mm + 2ppm X D) m.s.e. with angle measurement accuracy of 5". [13]. 2- Kern "GKO-A" Automatic level used for measuring elevations separately for comparisons and bench mark fixing. 3- Steel tapes used for measurements and checking purposes at various stages. 4- Various software as AutoCAD, Surfer, Excel, Text editors, etc.[14],[15]. III. FIELD WORK Prior to work with the total station, several control points have been carefully selected, marked, referenced, and named. These are selected to have the most accessibility and visibility to the most corners of nearby buildings and other control points. They are chosen at more stable and safe places out of the reach of humans and traffic. At many places, dense buildings limit the selection of ideal points on the ground. Hence, roof tops were chosen to setup instruments. These points should be observable from more than a single instrument location in order to fix the triangulation skeleton and reduce the errors before commencement into the details of hundreds of terrain points. At each setup of the instrument, the user performs centering and leveling. He feeds essential startup data, i.e. heights of instrument and prism, coordinates of the occupied point, name of the file to store data and ID of the first target point. Arbitrary coordinates can be fed first in the field which will be transformed and corrected later to any desired shifting or rotation using computer software. Air temperature and pressure are fed for calculating corrected outputs that are done internally by the instrument. The user takes a back sight reading towards any known control or any distinct mark that is visible from other locations. This will be used later to link to other locations while proceeding the work. In many working days, two or three prisms were used simultaneously to enhance the productive speed of work especially when planimetric and contouring are to be collected in the same run of work. Care was taken to use the same geometric configuration to all prisms within a single instrument setup. To improve the output results of elevation "Z coordinate", levels of points at key locations were measured using Kern instrument to compare results with those obtained using the total station. For each location of the instrument, the surveyor opens a new data file having the same name of the occupied point where all data captured will be stored. Then he feeds the coordinates of the instrument ground location. It is possible to feed arbitrary ground coordinates as this will be easily corrected during office work as will be explained later. He then feeds the ID number of the first target point. This ID will be successively increased automatically while doing more measurements. At each prism location, the instrument saves the following sample line of information about that specific point, referring to Point ID, N, E, Z .
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 159 84,3098.098,3211.456,211.987 During the list of measurements within a single setup of the instrument, the surveyor keeps brief notes about key observed points showing the point ID and small description of the ground point being observed see Figure 2. His notes will be helpful in drafting the details. For each setup, at least two common points have to be observed that will be observable from another instrument location(s). These (control) points will be used later to link different parts of the work. Fig. 2. Field notes describing a surveyed point Usually there are two types of observable target points. First, points that are used only for planimetric details, i.e building corners. In this case the prism height above ground point is not required. According to the ground obstacles at the target, the prism holder can raise or lower or even hold the prism rod leaning out of vertical as far as keeping the horizontal location of the prism in the right place, see Figure (3a and 3b). In the second type of observable points where ground contouring is required, the prism man have to hold the prism pole vertically over the desired point that represents the actual terrain at the spot as in Figure 3c.. In many cases, according to the ground configuration at the spot, it is possible to use the same point for planimetric and elevation details if the prism is held vertically over the right surveyed point. a b c Fig. 3. Positioning the reflector. (a, b) Applicable only for planimetric mapping. (c) Applicable only for contouring North Fence No. 84 South corner of fence No. 85
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 160 Apart from total station surveying, the author performed a major leveling survey that extends over the whole area comprising 29 elevation control points. A leveling network was created and solved using least squares methods to obtain the minimum error distribution [16], (Figure 4). Difference in elevation between two points at the ends of any leveling line have been given a weight that is inversely proportional to the distance between the points. It was necessary at many network lines to repeat measurements to obtain consistency in the results. The total length of the network lines was more than 10 Km. The locations of network points were note optimized due to limited accessibility. Adjusted elevation values have been used during stages of data analysis to check the validity of total station elevation results and fix new bench marks. Fig. 4. Network of leveling IV. OFFICE WORK After completing field data collection in the form of saved files as many as the number of occupied instrument stations, files are exported to the computer using the appropriate hardware and software links. Each data file representing the details obtained from a single instrument location was treated as explained in the following sequence of steps. 1- Open the file using Excel program and add location information of the instrument in the form explained in the following example as the first line of data file. V,689.086,5432.905,234.567 Where the text V represents the name of instrument location, with its N,E,Z coordinates. Use the coordinates already entered in the field. 2- If the instrument point elevation Z was also fed arbitrarily in the field (see field work steps), correct the column of Z coordinates of all points in the file based on its true elevation values. For all points that are not suitable for contouring (see Figure 3a,b),
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 161 modify point IDs by adding a special symbol. For example: If point V rests on high sidewalk of a building it will not represent actual ground contouring point, symbolize the ID "V" into "V>>>>", to be as follows in the coordinate line. V>>>>,689.086,5432.905,234.567 3- Draw a continuous line (polyline) that joins all point vertices according to their sequence of collection in the file. At each vertex write down a text showing the ID number of the point. Write each point ID Prefixed by the name of the instrument station. For example V_T (prism point T as observed from instrument station V) V_56 (prism point 56 as observed from instrument station V) Save the result as AutoCAD drawing having the name of the instrument location. See Figure 5. The author found that joining of sequential surveyed points with a continuous polyline is more helpful in tracing points and identifying various key locations. Fig. 5. An example of lines joining all surveyed points sequentially from a single instrument setup. Each vertex represents a numbered point 4- Repeat the previous steps for other instrument setups of the whole surveying work and save each result into individual drawing file. 5- Add or collect all partial drawings already obtained from the previous step using Copy/ Paste commands within a separate AutoCAD window. 6- In the collection AutoCAD file, successively use the (Align) or (Move and Rotate) commands to join each two adjacent parts together using common points until all parts compose a unified single drawing of the whole area in the manner shown in Figure 6. Save the result drawing.
  8. 8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 162 Fig. 6. Translation and rotation to align all adjacent parts and unify the drawing 7- At this stage shift and re-align the whole drawing to a desired location according to known world coordinates (or as required) of at least two points using Move /Rotate commands. See the result of this stage in figure 7. Fig. 7. The whole collection of surveyed details linked and realigned into a unified world coordinates
  9. 9. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 163 8- It will be helpful to insert an aerial photograph of the area or to overlay the Google earth image and adjust its location and scale on the drawing. This can guide drawing details of landmarks and probably discover any errors or observe discontinuity of the data. 9- Field notes about each point ID are used at this stage to draw lines that join points of interest of individual map components (see Figure 2.). Road and drain sides, fences, and building corners are gradually constructed. Incomplete data as those of unsurveyed features and boundaries are left for later field verification and can be completed using steel tape measurements later. The result is a plan drawing of the area that can be trimmed and annotated as required as shown in Figures 8 and 9. b _ 1 1 0 v 1 _ 7 7 v 1 _ 9 2 v 1 _ 9 4 v 1 _ 9 1 n2_215>>>> v 1 _ 7 2 v 1 _ 7 9 v 1 _ 8 7 v 1 _ 7 3 v 1 _ 7 0 v 1 _ 8 9 n2_214>>>> v 1 _ 8 5 v 1 _ 8 6 v 1 _ 7 8 v 1 _ 8 0 n2_213>>>> v 1 _ 7 5 v 1 _ 7 4 m1_160 m1_158 v 1 _ 7 6 b _ 1 0 6 b _ 1 0 4 v 1 _ 5 3 v 1 _ 9 5 > > > > v 1 _ 9 7 > > > > v 1 _ 9 8 b _ 4 9 b _ 1 0 5 b _ 4 3 b _ 4 6 v 1 _ 5 6 v 1 _ 8 1 v 1 _ 9 9 v 1 _ 1 0 1 n2_213>>>> v 1 _ 8 2 Fig. 8. Corners of a fence and small building before and after joining vertices according to field notes Fig. 9. Part of the final planimetric map 10- To prepare for leveling and contouring, refer to the output of step 7. Delete all lines from the drawing, and also delete all lines that contain the text symbol of ">>>>" as these points are not usable for contouring calculations. It is favorable at this stage to view the continuity of samples and the locations of sparse data to decide whether or not to add or correct field work of the surveyed points. See Figure 10.
  10. 10. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 164 Fig. 10. The drawing ready to extract X,Y,Z coordinates of elevation points 11- Extract X,Y,Z coordinate values from each vertex of the drawing and save the file in the form of (.txt or .dat). 12- Using appropriate contouring program such as "Surfer", grid the final coordinates data file and produce contours or 3D views of the surveyed area. See Figures 11 and 12. 240 2 4 0 245 2 3 5 2 4 0 23 5 23 0 2 5 0 25 0 2 4 5 24 0 2 4 0 2 4 0 2 3 524 5 2 5 0 22 5 24 0 2 4 0 2 30 22 5 23 5 2 4 0 2 3 5 2 3 0 2 2 5 23 5 2 4 5 245 2 5 0 2 4 5 2 4 0 2 3 0 24 5 2 3 5 245 240 245 250 240 Fig. 11. The final contour map Fig. 12. 3D view prepared from elevations and satellite image (Google Earth)
  11. 11. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 165 TABLE II TARGET DISTANCE AND THE MEASURED AND MODELED ELEVATION ERRORS Distance away from the total station m. Original error in elevation m. Modeled error using regression formula 399.94 0.012 0.023695 129.7825 0.016 0.002083 158.313 -0.000 0.004365 557.3546 0.035 0.036288 898.4301 0.067 0.063574 907.5783 0.062 0.064306 903.5818 0.074 0.063987 V. A NEW METHOD TO IMPROVE MEASURED ELEVATION ACCURACY It is reported that elevations obtained using total station surveying are prone to errors [5]. The major causes are related to uncertain measurements of atmospheric temperature, pressure, humidity etc along surveyed lines. These may cause the line of sight to depart from the straightness due to refraction and other errors. In this work, the author presents a new method to reduce measured elevation errors. Comparing elevation differences as obtained from ordinary leveling with those obtained from total station surveying is shown in Figure 13. Ordinate values represent error in elevation, while abscissa is the distance of surveyed point away from the instrument location. Data from one instrument location is shown. It is noticed that in general, the error increases with the increase in distance. The error was modeled in the form of inclined line using regression analysis. Accordingly, elevation correction can be made at any specific target location using its distance from instrument. For this specific instrument setup the following formulae (1,2) can be applied to reduce errors. Y= 8E-05 * X - 0.0083 ………………..1 Ei = E ± Y ………………..2 Where Y denotes modeled elevation error at distance X meters from instrument. Ei, E denotes improved and original measured elevations respectively. y = 8E-05x - 0.0083 -0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0 200 400 600 800 1000 Distance m Elevatinerrorm Fig. 13. Elevation error Vs. distance collected from an instrument location
  12. 12. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 166 Applying the resulting regression formula to the original measurements from the specified station location yields Table 2. All total station measured elevations of this specific instrument location can be corrected using this formula by applying equations 1 and 2. VI. CONCLUSIONS In this work the author presents a systematic methodology in collecting and reducing field data to obtain planimetric and contour maps simultaneously. This method should reduce error and time of field work. A formula is derived to be used for correcting errors in elevation results. The contour map produced by this work shows high degree of fidelity. The 3D version was produced by draping the satellite photographs obtained from Google Earth onto the elevation data of the selected region. It shows a great deal of details and improves the appearance of contour map. It should be emphasized that recently there are new developments in technologies of total stations that may improve performance. These are ranging from reflectorless, robotic to smart stations. However, their prices are considerably higher. REFERENCES [1] Wolf, P. R (2002), “Surveying and mapping: History, current status and future projections.” J. Surv. Eng., 128,3, 79–106. [2] T.R. Blachut, Chrzanowski, A. and Saastmoionen, J. H., (1979), "Urban Surveying and Mapping ", Springer-Verlag, New York Inc. [3] Kavanagh F. Barry, (2010), "Surveying With Construction Applications", 7th Ed. Prentice Hall. [4] Charles D. Ghilani, P. Wolf, (2008), "Elementary Surveying An Introduction to Geomatics", 12th ed. Printice Hall. [5] Ayhan Ceylan, Cevat Inal and Ismail Sanlioglu, (2005), “Modern Height Determination Techniques and Comparison of Accuracies”, Proceedings. From Pharaohs to Geoinformatics, FIG Working Week 2005 and GSDI-8., pp. 16-21. April. [6] F.Yildiz, H.Karabork, M.Yakar, C. Altuntas, L.Karasaka, A. Goktepeb, (2007), "Modeling by Advanced Total Station', XXI International CIPA Symposium, pp. 01-06. [7] Lerma, J. L., and Scherer, M., (2009) "From the Conventional Total Station to the Prospective Image Assisted Photogrammetric Scanning Total Station: Comprehensive Review", J. Surv. Eng. Vol. 135,4, pp. 173-178. [8] Sami H. Al-Ali, (2011), "The Practical Applications of the Electronic Total Station and Computerized System in Engineering Surveying." European Journal of Scientific Research. Vol.55 No.1, pp.125-153. [9] Nathanson J. A., Lanzafama, M. T., and Kissam, P., (2006), "Surveying Fundamentals and Practices ", Pearson, Prentice Hall, New Jersey. [10] A.L. Allan., (1993), "Practical Surveying and Computations ", Butterworth-Heinemann Ltd. , second edition, London. [11] T.B. Afeni, F.T. Cawood . (2013)," Slope Monitoring using Total Station: What are the Challenges and How Should These be Mitigated?". South African Journal of Geomatics, Vol. 2, No. 1, February 2013. [12] Kontogianni V, Kornarou S, Stiros S.,(2007)."Monitoring with electronic total stations: Performance and accuracy of prismatic and non-prismatic reflectors". Geotech News 2007;25(1):30–3.
  13. 13. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME 167 [13] Topcon Corporation, (2009), “Topcon GTS-235 Total Station Guide” [14] E. Finkelstein, (2005), "AutoCAD 2005 and AutoCAD LT", Wiley Publishing, Inc., USA. [15] Golden Software. (2009), "Surfer Software - 9, Surface Mapping System, Instruction Manual", Golden Software, Inc., Colorado. [16] Ghilani, Charles D., Paul R. Wolf.(2006),"Adjustment computations : spatial data analysis'' 4th ed. John Wiley & Sons. [17] Manish H. Sharma and Dr. C.H. Solanki, “Liquefaction Hazard Mapping”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 1, 2013, pp. 52 - 70, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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