Earth Curvature and GPS Surveying - Essay Example

May 26, 2009 Earth Curvature and GPS Surveying Introduction The Global Positioning System is a satellite based system that was established and maintained by the Department of Defence. The usage of the system by civilians varies from navigation to mapping to highly accurate surveying(sub centimetre level accuracy). With the use of the dual frequency real time kinematic GPS equipment, differential GPS surveys that are fast are provided with efficiency and extreme accuracy without post processing. The surveys are consistently accurate to the sub centimetre level. When the GPS base is established on a known latitude and longitude, and if post processing is applied to the base station, standardized coordinates for GIS mapping is provided, or any other application that requires coordinates based on latitude and longitude, UTM zone, State Plane Zone, or any of the standard zones and map projections. GPS is a tool that is used for the precise positioning of points. It operates through satellites which will send out signals to our receiver (this is the thing on the tripod). The receiver will transmit the signals to the data collector which will store the data. The data are downloaded into the computer, and the computer software determines from the data input the exact position of our point within a few millimetres In the Traditional Total Station Surveying, the primary function of the field surveyor is to measure, do mapping, and observing. The most important tool for these purposes is the total station. It incorporates a distance meter for the measurement of distances and a theodolite for the measurement of angles done with one instrument. The total station system of measurement is sending a beam of infrared light towards a prism that is normally supported by either a tripod of a pole. The light will reflect off the prism directly back to the total station. Measuring the time it takes for the light to return, the total station would calculate the distance away that the prism is. The information that the total station measures is then recorded in a data collector which will be downloaded into a computer. The data collector is often termed as the field computer because it enables the surveyors to calculate the coordinate geometry in the field and would figure out the proper position in which to put our stakes. GPS in land surveying has its requirements. Accuracy is the degree of perfection which is obtained in the measurements, while precision is the degree of refinement of measurements. High technology equipments that are used does not guarantee accuracy but precision may be improved if we follow directions and stay within the operating limits of the equipment. The proper use of the right equipments may guarantee the precision of the equipment. In the study, we ask the question of what GPS mean. It is a system capable of providing position information anywhere on earth. It is a constellation of orbiting satellites making various orbits around the earth. The user receivers acquire signals and determines it position. GPS was developed by DOD and it costs around $10 billion. This is a triangulation based technology. GPS is used as an all weather operation and it is always available with its 24/7 operations anywhere and everywhere. It is very economical with increased productivity and improved customer care and service. Its accuracy is dependent to its 3-D data, velocity and timing. The GPS is used in land sea, and airborne navigation, surveying, geophysical exploration, mapping, and geodesy, vehicle location systems, farming, and transportation systems. Our telecommunication infrastructure applications include network timing and enhanced mobile users. The global delivery of precise and common time to fixed and mobile users, are also engaged in the system. The GPS system component covers the user segment, the control segment and the space segment. The users are the military and civilians. The equipment may be portable and fixed. The equipment is used for navigation, surveying and GIS. The control segment makes up the ground facilities which in turn are responsible for satellite tracking and telemetry. Orbit and ephemeris computation with uplinking of the computed data and supervision of the daily management of the space segment including the five ground control stations which is the monitor stations and one master control station. The master control station is responsible in receiving tracking data from the monitor stations and calculates satellites ephemeris. It also adjusts satellite clicks, and maneuvers satellites, if necessary. It encrypts signals and maintains GPS reference systems(WGS 84) In the space segment, there are constellation of 24 satellites in six orbital planes around the equator with 4 satellites per orbit. There are also orbital planes that are inclined 55 degrees from the equator. The triangulation equation has 3 variables. These are, where, exactly are the location of the satellites. How ling will it take for the radio signal to travel the distance and how far is the point from the satellite. From orbital mechanics, the location of satellites are determined. A manual of orbital information for all satellites are stores in each satellite. The ground control-stations continuously update location information of each satellite, and transmit it to them (i.e. ephemeris) Results of Surveys done at the National Watersports Centre, Holme Pierrepont, Nottingham The first part of the field day was the establishment of the length of the rowing lake. At this point there were some errors in the measurements of the length of the rowing lake but the group was able to make corrections. There were suitable adjustments made until the errors were finally corrected. The second part was the establishing of a base station. The recording of the end of the rowing lake was done using the GPS equipment and later in the day we took a check on the measurements made in the first part of the field data gathering activity. The field results were later edited, and the result of the computations are as follows. From the data gathered, we will be able to compute for the value of the northings and eastings These northings and eastings are called the coordinates. The tabulations below represents the results of the coordinates. Survey Results The field work went thru smoothly. The first step that was done was establishing the station in the corners of the rowing lake, assigning points A,B, C, and D. The instrument was placed on point A and took a shot at point B. At this point the horizontal distance from point A to point B was recorded. The horizontal angle formed from point A to point B was recorded. The vertical angle was also recorded we notice that the northings of point D is somewhat erroneous 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. Corrected Survey Results Computations Field data Station Easting Northing Height A 462574.184 340049.414 18.168 B 462610.589 340009.591 18.198 C 460965.890 338513.505 17.815 D 460934.110 338484.048 18.053 Computations: From the field data, we will check by computation the length of A-B Taking data from the eastings and northings of point A and B For Line AB Easting Northing 462574.184 340049.414 - 462610.589 - 340009.591 36.405 39.823 Line Ab = where a = difference of eastings of A and B = b = difference of northings of A and B = Line AB = 53.956 For Line BC Eastings Northings 462610.589 340009.591 460965.890 338513.505 1644.70 1496.09 Line BC = Line BC = 2223.158 For Line CD Eastings Northings 460965.890 338513.505 460934.110 338484.048 31.780 Since the northings of line CD is not correct. We will solve for the correct northings. We will have to get the length of line CD from the field data that was recorded during the field work. Line CD = 46.797 (Line CD)2 = a2 + b2 = 2 + b2 b2 = (46.797)2 - (31.780)2 b = b = 34.35, we can now solve 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 From the table of the coordinates, we will be able to compute for the bearing, azimuth departure and the latitude. By using a programmable calculator that is especially used in the computations of surveys, I achieved the following results, Bearing Distance Azimuth Latitude Departure A-B S 4223' E 54.009 31737' -39.894 +36.407 B-C S 4619'W 2223.876 4619' -1535.969 -1608.236 C-D N 4246'W 46.796 13724' +34.354 -31.775 D-A N 4619'E 2223.628 22619' 1535.969 1608.236 After we have computed for the bearing, we can now compute for the distance between the stations. We can also solve for the azimuth. The departure and latitude can also be computed. In the early days of surveying, all computations are done manually. Calculations done manually are more prone to mistakes. The surveying instruments used are even suggestive of errors. These days, surveying instruments results are more precise and accurate. There are scientific calculators which can be programmed to perform the computations of 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' E Distance = 54.00 Azimuth = 317.37' Int. Angle = 8842' At Point B Bearing = S 4619' W Distance = 2223.158 Azimuth = 46 19' Int. Angle = 91 18' At Point C Bearing = N 4246' W Distance = 2223.876 Azimuth = 137 24' Int. Angle = 89 05' At Point D Bearing = N 4619' E Distance = 46.796 Azimuth = 226 19' Int. Angle = 90 55' Sketch of the Rowing Lake Plotted by Coordinate System References Land Surveying, Introduction to Land Surveying, August, 2001,2001, JS WebDesign, May25,2009.. Surveying, Land Survey Definition, 2002, Mc Graw Hill Companies, Inc., May 25,2009 . David, Foote, and Kelly, Surveying, 1974, Merriam School & office Supplies Co. Russell C. Brinker & Roy Minnick, 1987, Van Nostrand & Reinhold (VNR) Read More