Food

THE EXPECTED ROLES AND PROBLEMS FOR GPS CADASTRAL SURVEYS IN EGYPT

Description
GPS has become the preferred positioning technology for geodetic control and mapping surveys. The use of GPS technique in land surveying proved a great efficiency and permitted to accelerate data acquisition and maintained the accuracy needed for
Categories
Published
of 17
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
Share
Transcript
  Proceedings of the 4 th  ICCAE  Conf. 14-16 May, 2002   ICCAE Military Technical College 4 rd  International Conference Kobry Elkobbah, On Civil & Architecture Cairo, Egypt   Engineering   THE EXPECTED ROLES AND PROBLEMS FOR GPS CADASTRAL SURVEYS IN EGYPT   Mahmoud El-Mewafi *, Mohamed E.A. Amin **, Ahmed Shawkey          ا        قا   ا  سا         ا   ح   ا   ط   ا   أ   ك  م             ا        عا  م        ا  ا        ا  .               ا   ي      ا   ا          ا   ه   ا  س   ك     ق  ا      ط        ي   ت        س        ا      ك  ا     ا  غ  ط   ا   ح   ا       ي                   ا .          ا   ك   ا   ض    ط   م            ح   إ   إ   ث     ا   ا  ه   ف    م   ي              ا    ا  غ  ط   ا   ح   ا       ي           ا      قا   ا  س   ح   ا .  ص       ا           ا      قا      م      ق   ا     خا     م   سا  ج    ش   ط      م      ا   ي  ا   ح    حم     ت   ق       ك   ت   إ      ح     ا  خا             ا . ي   ع  ت    ب   ي   ا   م   ا         ا   ص     ا   ض   ث   ا   ت      ك        ا  ي                   ا    ا  غ  ط   ا   ح   ا       ي         ا        قا   ا  سا      م  .  Abstract GPS has become the preferred positioning technology for geodetic control and mapping surveys. The use of GPS technique in land surveying proved a great efficiency and permitted to accelerate data acquisition and maintained the accuracy needed for Cadastral and topographic surveys. The aim of this study is to introduce outline recommended procedures for set up, automatically, topographic and cadastral surveys in Egypt from survey data files obtained with GPS method with a high accuracy. Results on the GPS equipment testing and calibrations following the proposed recommended practices   have been presented together with the GPS survey results over the boundary markers of the selected cadastral lots. * Associate Professor, Public Works Dept., Faculty of Engineering, Mansoura University, Egypt  ** Head of Civil and Architecture Eng. Dept., Military Technical College Cairo, Egypt ***  Eng. Civil Engineering department, Military Technical college Cairo, Egypt    1.   Introduction The use of the Global Positioning System (GPS) is now being adopted and used by the surveying profession. Traditionally, GPS has been used for high precision geodetic survey, but increasingly it is being used for cadastral surveys. GPS has recently become an important survey and mapping tool to supplement and, in many cases, replace conventional techniques because of its advantage of accuracy, efficiency and cost effectiveness[Barnes, G. and M. Eckl, 1996b]. A Cadastral survey is a survey conducted to obtain the data needed for the preparation of a Cadastral map. A Cadastral map is simply a drawing that shows the natural and artificial features of an area. This data consists of the horizontal and vertical locations of the features to be shown on the map. The major trend over the last decade however, has been to convert these cadastral maps to digital form and there by create digital cadastral databases [Tommy Österberg, 1999]. The Egyptian Survey Authority (ESA)   is now well advanced in creating digital cadastral databases. A big issue however with regard to the digital cadastral databases in urban and rural sectors concerns the problems associated with updating and upgrading these digital cadastral databases, particularly from the point of view of the authors. These problems are related to: planning a GPS cadastral survey and how the coordinates are to be determined through appropriate connection to survey control; testing/calibration of GPS equipment; field procedures for operating the equipment, documentation, quality assurance and verification procedures, and; office procedures for data reduction and result submission. This paper concerned with test results on the GPS equipment calibration procedures, GPS survey results over the boundary markers of the selected cadastral lots, which has followed by the “recommended practices for field and office procedures”, are also presented. Besides this some points of the building corners were observed by means of a rapid static technique. These measurements are not subject of this paper.    2. GPS Equipment Calibration GPS equipment, software and procedures should be tested before general usage. This can be achieved by making measurements and processing data over known baselines or a network of points [SES et al., 1999]. Unlike EDM equipment, GPS receivers cannot be calibrated for scale because the definition of scale is inherent in the satellites and orbit data. However, antennas and tribrachs can be calibrated for centering errors. Antenna centering errors are generally not significant when geodetic quality equipment (e.g., with micro strip antennae) is used for cadastral surveys. However, the Surveyor is entitled to request a calibration test if there is reason to doubt the GPS results - particularly those on short lines [GPS Guidelines, 1999]. For this reason, a number of control tests were undertaken at a cadastral test site on the Military Technical College (MTC) campus in Kobry El-koba, Egypt, it is located on lat. 30 0  05 ’ 00 ’’  and long. 31 0  17 ’  30 ’’  see fig. (1). Figure (1): Test area for GPS cadastral survey      The list of Three  Leica dual frequency GPS receivers being used in the test following field criteria and processing requirements given in Table 1 Table (1):  GPS equipments, field criteria and processing requirements Used in the tests GPS equipments   Type of receivers  Leica System 300 (L1& L2) Number of receivers tested 3 (R1, R2, R3)   Antenna with splitter 1 (for each test) Processing software SKI version 2.11   Field test criteria Observation length 10 minutes   Recording Interval 15 seconds   Number of satellites  5   GDOP  6   Sky Clearance  90 %   Processing requirements   Session length 10 minutes   Ambiguity Resolution Fixed   Used Cut Off Angle 15 o   Frequency used L1 and L2 2.1.   EDM Baseline Test An EDM baseline test   is performed in order to ensure that the operation of a pair of GPS receivers, associated antennas and cabling, and data processing software, give distance results that can be compared with calibrated baseline data. GPS can be used to measure the three components of a baseline, that is, expressed as either: (i) relative latitude, longitude and height, or; (ii) relative Cartesian coordinates with respect to a global geocentric reference frame, or; (iii) distance, azimuth and height difference between the two antennas. However, EDM baseline testing only considers the distance component. However, it is assumed that if the GPS equipment can verify the known distances between the markers on the pillars of the EDM baseline, the equipment is in good order and capable of delivering baseline solutions that are within specification [BOO et al., 2000].    A series of EDM baseline test have been carried out at the existing EDM baseline calibration test site in MTC on the May 2001. The site is being maintained by MTC and their layout is shown in Figure 2. Figure: (2) EDM baseline test site The EDM test site comprises of six (6) pillars separated at specified interval. The length between pillars has been routinely measured and documented as the published true values. The test has been carried out using GPS rapid static technique. One receiver (R1) was remained at the Pillar 1 during the entire observations while the other one(R2) was roving. The differences between GPS computed distances and their corresponding EDM values for each pair of pillars (receivers) are given in Table 2. Table (2):  Differences between EDM and GPS values for R1/R2 receivers Baselines   (Pillars)   Distances (m)   Differences   (mm)   EDM (m) R1- R2 (m) 1-2 64.21372 64.21271 1.01 1-3 211.5805 211.5853 -4.8 1-4 469.1565 469.1687 -12.2 1-5 627.2452 627.2404 4.8 1-6 884.327 884.335 -8 The results indicate that, for both pairs of the receivers, differences of less than 13mm has been given. This shows that the GPS equipment set being used are in good condition.
Search
Similar documents
View more...
Tags
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks