Earth Curvature and GPS Surveying - Term Paper Example

Earth Curvature and GPS Surveying Introduction The global Positioning system (GPS) is a space based, microwave, a 24 hour, all-weather, global military navigation system design, that is deployed, financed and managed by the U.S military authorities. Since the declaration of operation of GPS in 1993, it already had an impact on the art and practice of the forms of positioning and navigation. However, GPS had already a remarkable impact on surveying, first as a technology for the “control surveys”, for which the purpose was first introduced into many countries during the early 1980’s before the full satellite constellation was available to navigation users. The application of GPS for control survey (geodetic survey) was the first civilian use of GPS which was well beyond that for which GPS was originally intended by its military designers. Today, GPS surveying techniques have completely replaced the other technologies such as Doppler satellite positioning and EDM as well for the traditional first and lower order control surveys. The adoption of GPS is not restricted to control survey applications only. It is now being used for cadastral, topographical and engineering surveying. The constraints are being aggressively addressed by the manufacturers, and it is predicted that GPS will shortly be used by the majority of surveyors and geomatic engineers. An important objective is to dispel the myths and incorrect perceptions of the capabilities and shortcomings of the technology. This is the result of people that are bewildered by the increasing GPS terminology. It is necessary to distinguish between the “GPS navigation” techniques based on the relatively imprecise pseudo-range observations and the GPS surveying techniques specifically developed for precise positioning applications. In addition to the specialist technology of GPS surveying, the sub categories of the conventional GPS surveying as well as the modern GPS surveying will be covered in these area. The contributions to the increasing popularity of GPS has been the evolution precise of GPS surveying from a difficult, expensive and complicated technology that could only be used in the so-called “static” mode to a technique that has a remarkable flexibility, including the fact that it is being used in the kinematic mode. This increases the number and range of applications that can be addressed by the GPS technology. It is necessary to understand the fundamental principles of the GPS operational procedures. Survey Results done at the National Watersports Centre, Holme, Pierrepont, Nottingham. At the site, it was necessary to measure the length of the rowing lake. It is also very necessary to make suitable adjustments and error correction. To establish a base station was the first thing to do, and the need to record the end of the lake using GPS Total Station equipment. Checking the measurements done for the earlier activity must also be included in the field data gathering. As any other surveying activity, The principal steps in surveying activity was followed in the data gathering. GPS Total Station was the instrument used. A station was set on a corner point, and it was assigned station A. The instrument was set on point A. Point B was also established at the other corner of the lake. At point A, shots were taken on point A. The horizontal distance from point A to point B was measured and recorded. Setting the instrument at due south, the horizontal angle from point a to point B was taken, as well as the vertical angle of point A to point B. The instrument was transferred and set at point B. A shot was taken from point B to point A to check the distance from point B to point A. Point A was given a shot from point B for the checking of the horizontal angles and the vertical angles as well. At point C, the same procedure was done. This time, from point C, Shots were taken at point A and B. This procedure was done to check the data that was earlier recorded at points A and B. At point D, the last station that was established, The procedure was repeated, Shots were taken at points A,B and C. The purpose of which is to check the accuracy of the data recording that was done in the 3 stations that was earlier shot. At this point, errors were detected and a need to make some adjustments in the survey results has to be done. However, the adjustments to be done must be presented with computations and the errors must be distributed to the different stations made. The check was detected when the attempt to plot the data gathered was executed. Point D does not conform with the computed coordinates and that the traverse computation of the rowing lake does not seem to close. This is an indication that there was an error in the data gathering. Errors usually happens in data gathering. This is one reason why a field office is always established in performing surveying jobs that could either be small or a big surveying project. Errors can be checked immediately at the field area. The following are the field data gathered from the surveying activity that was done. These data are the horizontal distance, horizontal angles, and the vertical angles taken from the different stations that was appointed. If we try to have a close look at the field data results and try to close the traverse computations, we will not be able to avail any result. The northings of point D is an erroneous result. We notice that the northings of point D is somewhat wrong in the survey results. If we try to plot the sketch of the coordinates, we will have an open traverse. This means that one of the points have a wrong coordinate. We must correct the error, or do the field data gathering all over again. The following tabulation will show us the corrected coordinates. I used a programmable calculator specially used in surveying to attain the results in the tabulations below. Here are the field data gathered where we are going to base all the computations that we are going to make so that we will be able to plot the exact figure of the rowing lake. Tabulated results of field data recorded At point A At point B At point C At point D A – B B – A C – A D – A HD- 54.008 HD – 54.039 HD – 2224.212 HD – 46.796 HL – 152 22 00 HL – 100 17 45 HD - 197 52 50 HL – 102 47 40 HR – 332 22 11 HR - 280 17 40 HR - 17 52 35 HR – 282 47 35 VL - 90 01 57 VL – 89 59 40 VL – 90 00 15 HL – 90 02 50 VR – 270 00 50 VR – 270 00 50 VR – 270 00 50 VR – 269 57 20 B – C C – B D – A HD – 2224.701 HD – 2224.760 HD – 2226.066 HL - 66 12 25 HL - 196 29 10 HL - 15 40 05 HR - 266 12 35 HR - 16 29 00 HR - 15 40 05 VL - 90 01 07 VL - 90 00 10 VL - 90 00 10 VR - 269 59 31 VR - 269 59 20 VR - 269 59 55 C – D D - B HD - 46.797 HD - 2225.438 HL - 106 00 20 HL - 14 16 25 HR - 285 59 20 HR - 144 16 25 VL - 89 56 20 VL - 90 00 05 VR - 270 04 00 VR - 269 59 25 From the field data gathered the coordinates are computed and written in tabulated form The result northings of point b is erroneous. Computations: We will check by computation the length of A-B from the field data Line A-B Easting Northing 462574.184 340049.414 462610.589 340009.591 36.405 39.823 Line A-B =  where a = difference of eastings of A and B =  b = difference of northings of A and B =  Line A-B = 53.956 For Line BC Eastings Northings 462610.589 340009.591 - 460965.890 - 338513.505 1644.70 1496.09 Line B-C =  Line B-C = 2223.158 For Line C-D Eastings Northings 460965.890 338513.505 460934.110 338484.048 31.780 We must correct the northings of line CD. At this point we need to use the data that was taken from the field in order to get the correct northing (coordinate) of line CD. Line CD = 46.797 (Line CD)2 = a2 + b2  = 2 + b2 b2 = (46.797)2 - (31.780)2 b =  b = 34.35, compute for the value of the northings of point D 338513.505 + 34.350 338547.855 For Line DA Eastings northings 462574.184 340049.414 460934.110 338547.855 1640.074 1501.559 Line DA =  =  Line DA = 2223.628 The tabulations is the corrected coordinates of point D We will be able to compute for the bearing, azimuth, departure and latitude by using the tabulations of the corrected coordinates of point D. A programmable calculator was used for the computations of the survey results Bearing Distance Azimuth Latitude Departure A-B S 42°23’ E 54.009 317°37’ -39.894 +36.407 B-C S 46°19’W 2223.876 46°19’ -1535.969 -1608.236 C-D N 42°46’W 46.796 137°24’ +34.354 -31.775 D-A N 46°19’E 2223.628 226°19’ 1535.969 1608.236 Before the digital instruments were introduced, all readings were done manually. Computations were done manually as well. Calculations done manually are more prone to mistakes. The instruments used in the surveys are even more suggestive to errors. Today, surveying instruments are equipped with digital readings for better precision and accuracy. More over, there are scientific calculators that are programmed to perform the computations of the survey results. In the data gathering that was done, the survey results that are presented are edited and then produced as professional topographic drawing. A sketch of the rowing lake was plotted using the coordinates of the survey results. At Point A Bearing = S 42° 23’ Distance = 54.00 Azimuth = 317°.37’ Int. Angle = 88°42’ At Point B Bearing = S 46°19’ W Distance = 2223.158 Azimuth = 46° 19’ Int. Angle = 91° 18’ At Point C Bearing = N 42°46’ W Distance = 2223.876 Azimuth = 137° 24’ Int. Angle = 89° 05’ At Point D Sketch of Rowing Lake Bearing = N 46°19’ E Plotted by Coordinate System Distance = 46.796 Azimuth = 226° 19’ Int. Angle = 90° 55’ References Brinker, Russell C., Minnick, Roy, Modern Geodetic Engineering Handbook. 1987. Van Nostrand Reinhold Company Czerniak, Robert J., Reilly, James P., National Transportation. 1998. Booksgoogle.com/books?isbn=0309061164 Davis, Raymond E., Foote, Francis S., Kelly, Joe W., Surveying, Theory and Practice. 1980. McGraw Hill Book Company. Gillesania, Dit. Civil Engineering Formulas Series. www.gertcrev.com. 2006. Diego Inocencio Tapang Gillesania Hans, S. & Rizos, C. 1995. A Suggested Procedure for on-the-fly Ambiguity Resolution for long Range GPS Kinematic Positioning .Proc. 4th Intl. Conf “Differential Satellite Navigation Systems DSNS 95” Bergen, Norway. Johnston, H., Redd, T., Tabrizi, A. GPS in Land Surveying. 2008. Edited by D. Spalton for the University of Derby. Kaplan, E. (ed), 1996. Understanding GPS: Principles & Applications. Artech House Publishers, Boston, London. Snay, R.A. 1986. Network Design Strategies Applicable to GPS Surveys using three or Four Recievers. Bulletin Geodesique. Principles and Practice of GPS Surveying, Chris Rizos, 2000. Read More