GE 414 Midterms Notes PDF

GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS GEODETIC CONTROL NETWORK 3. JAN 1901 GEODETIC CONTROL SURVEYS Start of actual fieldwork, only in the performed to e...

GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS GEODETIC CONTROL NETWORK 3. JAN 1901 GEODETIC CONTROL SURVEYS Start of actual fieldwork, only in the performed to establish an accurate vicinity of the garrisoned places positional framework from which nationwide 4. 1901-1906 supplemental surveying and mapping are System of military telegraph and referred cable lines used to establish a large determination of the precise position of a number of astronomical stations number of stations distributed over an area, were scattered throughout the taking into account the curvature of the islands earth, to serve as primary reference or as The precise latitude and longitude of check points for other subsequent surveys these stations were determined, and to be used in engineering projects eventually connected by a performed to far more rigorous accuracy triangulation net and quality assurance standards than those More surveys to meet the demands for local control surveys (project control) of the military and the local distinguished by use of redundant, commerce interconnected, permanently monumented About 90 charts already produced control points 5. 1907 used also to effectively and efficiently Five vessels doing hydrographic and monitor and evaluate external deformations topographic surveys in large structures such as dams Computers and draftsmen sent to COMPONENTS OF A GEODETIC CONTROL Manila office engaged in compiling NETWORK charts from the new surveys 1. Horizontal Control About 153 catalogued charts provided by two or more points in produced the ground, permanently or 6. 1920 semi-permanently monumented, and First printing plant in Manila (all precisely fixed in position previous maps were printed in horizontally by distance and Washington) direction, or coordinates 7. UNTIL 1942 established by performing Expansion of surveys to whole triangulation, trilateration, traversing, Philippines or by the use of GNSS INSTRUMENTATION 2. Vertical Control 1. Direction Theodolite provided by benchmarks in or near 2. Steel Measuring Bands the track to be surveyed, and it 3. Geodimeter becomes the basis for all elevations 4. Total Station and in portraying the relief of the 5. Gravimeter area 6. GNSS usually established by running lines TRADITIONAL SURVEY POSITIONING of differential levels TECHNIQUES GPS surveying may also be used, 1. Horizontal Positioning but elevations must be converted to Astronomical Techniques orthometric heights first in order to Triangulation be acceptable Trilateration HISTORY OF GEODETIC SURVEYING IN THE Traversing PHILIPPINES 2. Vertical Positioning 1. 1898-1900 Precise or Geodetic Leveling Americans took over the Philippines Trigonometric Leveling from the Spaniards Barometric Leveling Discovered inaccurate maps and WHY DO WE HAVE MANY FRAMEWORKS? charts Numerous reference ellipsoids/datum 2. DEC 1900 Various geoid models Appeal to have the island surveyed Many countries and charted Advancing Technologies CGSD was established in Manila GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS THE GLOBAL AND THE LOCAL GEODETIC GEOID MODELS : EGM REFERENCE FRAME Earth Gravitational Model 1. Global Reference Frame Developed in a collaborative effort of: there should be only one truly global NASA Goddard Space Flight Center reference frame National Imagery and Mapping 2. Local Reference Frames Agency (NIMA) Since each country/area in the Ohio State University surface of the earth uses a frame predecessor models: that is appropriate to the local OSU-91A model surface, there are infinite number of JGM-2 model local frames based on: WORLD GEODETIC SYSTEM OF 1984 (WGS84) surface gravity data a conventional terrestrial reference system altimeter-derived gravity anomalies (CTRS) extensive satellite tracking data The definition of this coordinate system (GPS, TDRSS, DORIS, TRANET) outlined by the International Earth Rotation direct altimeter ranges Service (IERS) as follows: EGM2008 It is geocentric, the center of mass This gravitational model is complete to being defined for the whole earth spherical harmonic degree and order 2159 including oceans and atmosphere. contains additional coefficients extending to Its scale is that of the local earth degree 2190 and order 2159 frame Can compute geoid undulations accurate to Its orientation was given initially by better than one meter BIH on 1984 Can be used with the WGS 84 reference maintained by the US DoD for its military ellipsoid using a set of precomputed purposes constants It was initially established using different GEOID MODELS : EGM terrestrial and extraterrestrial positioning EGM96 methods such as the Doppler systems Gpm3e97a (1997) The most recent WGS84 realization GPM98A, B and C (1998) adopted by the US DoD is the WGS84 Other national geoid models (G1150) THE PHILIPPINE GEOID MODEL INTERNATIONAL TERRESTRIAL REFERENCE Based on “The Evaluation of the Geoid in FRAMEWORK (ITRF) the Philippines” by A.H.W. Kearsley established by the Terrestrial Reference Part of the 1st order geodetic control survey Frame Section of the Central Bureau (CB) component of the Natural Resources of the International Earth Rotation Service Management and Development Project (IERS) (NRMDP) The implementation of the ITRF is based on Describes the investigation into the detailed the combination of Sets of Station geoid for the Philippines coordinates (SSC) and velocities derived Based on: from observations of space-geodetic Altimetrically-derived gravity data techniques Terrestrially observed gravity data The global solutions are: ITRF88, 89, 90, Gravity profiles in Northern Luzon 91, 92, 93, 94, 96, 97, 00, 05 , 08 (mountainous; 170 km) and Eastern RELATIONSHIP OF ITRF AND WGS84 Mindanao (flat; 75 km) WGS84 and ITRF94 are practically identical Geopotential Models (with respect to its parameters and - OSU86 E and OSU89A definition) DEM The positions that can be derived from - ETOPO5 world data of 5’ mesh of WGS84 and ITRF conforms up to about ±2 heights cm accuracy - From digitized topographic maps of 1:250,000 scale by CERTEZA GPS Control over BM with known MSL Heights GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS Problems with the data: The original survey was second order or Low density of gravity data lower, controlled by 98 measured base Satellite altimeter data contains lines, 52 observed azimuths and 49 latitude free-air anomalies over land areas and telegraphic longitude stations Some observed terrestrial data over Geoid and ellipsoid were assumed to the oceans are in conflict with those coincide at the datum origin, i.e., deflection from satellite altimetry of the vertical and geoid-ellipsoid separation Data file appears to contain large were defined as zero errors THE NATURAL RESOURCES MANAGEMENT The gravity profiles and DEM show AND DEVELOPMENT PROJECT (NRMDP) very little correlation hence no The proliferation of geographic information high-frequency information can projects necessitated the establishment of be derived standards and coordination mechanisms in DEM was derived from a weak order to ensure compatibility of geographic mathematical method and is not information systems, facilitate data reliable for deriving terrain exchange, and optimize use of resources corrections The NRMDP (1989-1992) of DENR Both OSU86E and OSU89A fit the recommended the use of National Statistical terrain equally (and poorly) Coordination Board’s (NSCB) coordinative Tests Show that the geoid heights have a set up in addressing the problems besetting precision of better than 10ppm the system The gravimetric N against those from An Inter-Agency Task Force on Geographic GPS/leveling identified a number of doubtful Information was created to promote and control stations which may be attributed to coordinate the efficient development, the errors in the orthometric heights management and utilization of geographic Better solutions of N were derived using information in the country smaller ring sizes NAMRIA, NSCB, HLURB, NSO, NCC, Certain biases exist for the N values near DPWH, DOST, BSWM, NEDA the gravity profiles 330 first-order stations, 101 second-order, THE ORIGINAL NETWORK 36 third-order Local datums were established at “Astro PHILIPPINE REFERENCE SYSTEM OF 1992 stations” that include Bancalan Island, Established by NAMRIA in 1992 thru Cagayan Sulu Island, Davao, Iligan, DENR-NRMDP in collaboration with the Misamis Oriental, and Zamboanga on Government of Australia Mindanao Island,Legaspi and Vigan on By law, it is thePhilippines’ standard Luzon Island, Ormoc and Tacloban on Leyte survey and mapping reference Island and Iloilo on Panay Island. frame/system However, the extent of coverage became A set of coordinates of all stations in the limited due to physical configuration of the new network country w/c rendered development of PRS 92 is not a new datum but an network especially inland not feasible by adjustment of the Luzon datum conventional surveying techniques. The original datum observations from Luzon Stations were established along the coasts. 1911, used in PRS 92, were not computed LUZON DATUM OF 1911 NAMRIA has published transformation Can be defined by the origin near San parameters for PRS 92 to WGS 84 Andres point on Marinduque Island in the The horizontal datum component was Southern Tagalog Region, stationed at undertaken using GPS using the guidelines Balanacan. based on recognized Australian Established in 1911 and is defined in terms specifications and practices and standards of position of station Balanacan: of the Hydrography Department (then, Latitude= 13-33-41 CGSD) of NAMRIA Longitude= 121-52-03 A national geoid model for the vertical Azimuth to Baltazar= 9-12-37 component was developed for the The reference ellipsoid used was Clarke Philippines with relative accuracy of 5 ppm Spheroid of 1866 where: and 8 ppm based on OSU89 geoid model, a= 6378206.4 m supplemented by local gravity data, where 1/f= 294.9786982 m gravity surveys were taken in Northern GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS Luzon in San Fernando, La Union to GEODETIC CONTROL NETWORK Cauyan, Isabela and in eastern Mindanao ESTABLISHMENT AND DENSIFICATION in Surigao City PHILIPPINE GEODETIC CONTROL NETWORK GEODETIC CONTROL NETWORK PHILIPPINE ACTIVE GEODETIC These control networks consist of stable, NETWORK (PageNET) identifiable points tied together by the country’s new positioning infrastructure extremely accurate observations. which utilizes signals from global navigation From these observations, datum values satellite systems(GNSS) (coordinates or gravity) are computed and a network of continuously operating published reference stations that provide real-time, These datum values provide the common high-precision geographic position data via basis that is so important to surveying and the Internet mapping activities. data generated by the network may be used an accurate positional framework from for surveying and mapping, aviation, which nationwide supplemental surveying navigation, military,scientific research and and mapping are referred monitoring, and agriculture, among others a system of precisely positioned, ACTIVE GEODETIC STATION (AGS) permanently marked stations distributed Each AGS is equipped with a geodetic over an area, taking into account the grade GNSS receiver and antenna, curvature of the earth, to serve as primary supplementary sensors (meteorological and reference or as check points for other tilt), router, uninterrupted power supply subsequent surveys to be used in (UPS) system, back-up battery, and other engineering projects accessories. the basic spatial framework for the control DATA AND CONTROL CENTER (DCC) and integration of surveys, mapping and all Serves as the AGN’s Information land related information Communication Technology (ICT) facility for RELEVANCE OF GEODETIC NETWORK online data processing, network monitoring, In surveying and mapping large areas, it is as well as data storage and distribution first necessary to establish frameworks of PRS92 MODERNIZATION horizontal, vertical, and gravity control. Further densification efforts by NAMRIA These provide a common basis for all Zero-order network surveying and mapping operations to Issues: ensure a coherent product. WGS84 refinement A reference system, or datum, is the set Effect of plate tectonics of numerical quantities that serves as a WGS84 refinement common basis. WGS84 (original) → PRS92 Unify and standardize all surveying data WGS84 (G730) – 1994 MEASUREMENT SYSTEM WGS84 (G873) – 1996 The combination of survey design, WGS84 (G1150)- 2002 instrumentation, calibration procedures, “G” – for GPS observational techniques, and data 730, 873, 1150 – number of weeks reduction methods reckoned from date of GPS full Upon selection of the measurement system, implementation a survey design can be started. The design THE PHILIPPINE GEOCENTRIC DATUM OF 2020 will be strongly dependent upon the Different datums give different coordinates "Network Geometry" specifications for that Effect of plate tectonics measurement system. Philippine plate moving NW with Of particular importance is the requirement velocity of 2-7mm per year to connect to previously established control (NIGS/Phivolcs) points. Effect on PRS92 GPS stations not monitored GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS the ability of that survey to duplicate already established control values. This comparison takes into account models of crustal motion, refraction, and any other systematic effects known to influence the survey measurements. LEVELS OF ACCURACY Different levels of accuracy are referred to as the "order" of a point. Orders are often subdivided further by a "class" designation. Datum values for a station are assigned an order (and class) based upon the RELATED DAOS, TECHNICAL MANUALS AND appropriate classification standard for each GUIDELINES of the three control networks. Order, Accuracy, Standards, and Specifications Geodetic Control Survey Accuracy/Standards: of Geodetic Control Network DENR Administrative Order No. 2007-29, Depends on the purpose and extent of the “Revised Regulations on Land Surveys” survey. US Army Corps of Engineers, Engineer Importance of standards: Manual 1101-1-1004, “Engineering and To provide a uniform set of Design: Geodetic and Control Surveying” standards specifying minimum Field Operations: acceptable accuracies of control Land Administration and Management survey for various purposes. Project 2, “Field Operations Manual Module To establish specifications for 2: Control Establishment” instruments, field procedures, and DENR Memorandum Circular No. misclosure checks to ensure that the 2010-13, “Adoption of the Manual on Land intended level of accuracy is Survey Procedures” achieved. US Army Corps of Engineers, Engineer Factors affecting accuracy: Manual 1101-1-1004, “Engineering and Type and condition of accuracy Design: Geodetic and Control Surveying” Field procedure Implementation of PRS92: Capabilities of survey personnel Executive Order No. 45, “Adopting the Philippine Reference System Of 1992 As REVISED REGULATIONS ON LAND SURVEYS The Standard Reference System For (DAO 2007-29) Surveys In The Philippines DENR Administrative Order No. 2005-13, ARTICLE 7 - SURVEY ACCURACY “Revised Guidelines for the Implementation Section 28. Control Surveys of the Philippine Reference System of 1992” For the purpose of this regulation and DENR Administrative Order No. 2010-17, consistent with the adoption of new survey Implementing Rules and Regulations (IRR) technologies, the Control Survey Accuracy on the Conduct of Inspection, Verification shall be as follows: and Approval of Survey (IVAS) in the Philippine Reference System of 1992 (PR92) STANDARDS The classification standards means that when control points in a particular survey are classified, they are certified as having datum values consistent with all other points Section 29. Cadastral Surveys in the network, not merely those within that a. Controls and Political Boundary particular survey. Surveys (3rd order : Municipal, 4th It is not observation closures within a survey oder: Barangay) which are used to classify control points, but b. Lot Survey (5th oder) GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS Section 30. Isolated Surveys Section 13. The Network Design shall be a. Original, subdivision, consolidation, made to conform to the following or consolidation-subdivision isolated conditions: survey (5th oder) The lines connecting the control Section 31. Mineral Land Surveys points within the network should a. Survey of Mineral Lands (4th order) create closed polygons with the Section 32. Forestland and National minimum number of sides, such as Park/Protected Areas Delimitation triangles that will create a rigid Surveys network. a. Depends on the area coverage The Network shall be designed so under the project control surveys that all stations or points included (similar to isolated surveys) therein have at least three (3) known PRS 92 control points. MANUAL ON LAND SURVEY OPERATIONS The designed Network should have (DMC 2010-13), PURSUANT TO DAO 2007-29 an adequate amount of redundancy: optimal number of ARTICLE 1 - GEODETIC CONTROL SURVEYS known points should be included, Section 2 with as many cross-ties and All Geodetic Control Surveys shall repeated measurements as be conducted in the Philippine possible. Reference System of 1992 (PRS The field observations shall be timed 92) using survey grade GNSS when the Position Dilution of receivers. Precision (PDOP) is low. Section 10. Designing Network of Section 15. Geodetic Control Monuments Controls a. The position of reference points shall The intervisibility of stations are not be defined and marked on the necessary in order to have a good ground by monuments of Network Geometry in the GNSS permanent nature in the form of a observations square base frustum. However, in the preparation of the b. Concrete monuments shall be Network Design, it is necessary that fabricated with reinforced steel bar the points selected can be (10 mm in diameter for vertical bars occupied, located in a stable and 8 mm in diameter for ties) and ground and shall not be affected satisfying the requirements of class by any construction activities in A concrete specifications in the ratio the near future. of 1:2:4 (cement, sand, and gravel). Swampy or loose soil areas should Sand and gravel must be clean, free be avoided. from dust or mud or other organic Section 12. Map of the project site matter. The available NAMRIA Topographic c. The concrete monuments shall be Map on the area shall be used as cast in place where they will be base map established. All the fixed controls (Old Control Section 16. Markings of Reference Points) based on the available Monuments records shall be plotted NAMRIA shall be consulted for The Points to be established shall be assignment of Code to the newly approximately plotted on the created provinces. selected locations The numbering of control points Caution shall be taken in order to shall be from 1 to 3000 for those scale the map correctly. The established by NAMRIA and 3001 distance between points is an and so forth for those established by important factor. LMB/LMS and other entities. Each station shall be numbered The name of the office or entity that properly established the control point shall be The Network Design’s final map may inscribed using only one word be modified upon the conduct of which could either be an acronym, Field Reconnaissance. GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS company name or surname of a ARTICLE 25 - GEODETIC CONTROLS person Section 186 To avoid duplication of numbers, the The NAMRIA shall verify the establishing entity shall coordinate correctness and technical accuracy with NAMRIA for the 1st and 2nd of the survey returns of the 1st and Order control points and with the 2nd Order Geodetic Control concerned LMS Regional Office for Surveys. the 3rd and 4th Order control points. ARTICLE 14 - MANAGEMENT OF SURVEY All the letters and numbers shall be RECORDS AND INFORMATION in “Arial Bold” Font Type, all Section 67. National Geodetic Network capital and shall be 2.5 cm in Information System (GNIS) height, 2 cm in width and 0.4 cm a. Consists of a national facility that in thickness with margins not less shall have the storing, updating, than 2 cm. along the edge of the reporting, transformation, data monument to give allowance for analysis, and security capabilities chipping. with online access for other It should bear the mark “GOV agencies. PROP” which stands for b. NAMRIA in coordination with government property. LMB/LMS shall develop the system c. NAMRIA shall publish (print and digital) the 1st and 2nd order PRS92 Geodetic Control Points, LMB and LMS shall do the same for 3rd and 4th order control points d. NAMRIA and LMB/LMS shall regularly update the GNIS and exchange digital copies of lists including name/designation, location, grid and geographic coordinates, and upon request, descriptions of the control points ARTICLE 8 - REFERENCE MONUMENTS Section 35. National Database of Section 19 Geographic and Plane Coordinates The establishment of geodetic (GPC) of all Land Survey Reference control covering the 1st and 2nd Monuments Order Accuracy shall be done only 3rd order and below – managed by using a GNSS Receiver. LMB There shall be at least three (3) New reference points – data receiver units per survey team. should be furnished to LMB for The employment of more than four updating of the National Database (4) Receivers is preferable. Online access between the DENR, Section 25. Connection to existing LMB, NAMRIA, and the LMS controls regional offices for data sharing and Connection shall be made to control efficient servicing of the public of the same or higher Order of Conventional control and GPS Accuracy with the following number surveying methods can be used for of observations: wide-area, high-order geodetic control densification. 1st, 2nd or 3rd order work can be achieved using conventional or GPS surveying techniques. GPS techniques are now generally used for most horizontal control surveys performed for mapping frameworks. GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS Conventional leveling methods TRIANGULATION STATIONS are used to determine orthometric Vertices of the triangles in a Triangulation height elevations of benchmarks system established for vertical control BASE LINE densification. Line in a system whose length is precisely For large mapping projects, known differential GPS may prove more Direction is known via Astro observations cost effective for densifying vertical CHECK BASE control. Known length and located at regular However, for small project sites or intervals or at the end of the system construction projects, conventional Serves as checks for computations spirit leveling is generally preferred. involving lengths of lines NETWORK ACCURACY Intended to measure the relationship between the control point in question, and the datum LOCAL ACCURACY Measures the positional accuracy relative to other points within the same network TRILATERATION SYSTEM Consist of joined or overlapping triangles Lengths of sides are measured Few directions are observed HORIZONTAL CONTROL SURVEYS Survey made to establish Geodetic Latitudes and Longitudes To also establish rectangular Coordinates of a network of ref. stations TRIANGULATION PROCEDURE 1. Reconnaissance 2. Strength of Figure for the Network 3. Erection of Signals and Towers 4. Angle Observation 5. Baseline Measurements 6. Astronomic Observation 7. Computations TRIANGULATION AND TRILATERATION PURPOSE OF TRIANGULATION Extensively employed to establish horizontal control for: Topographic Mapping Charting water bodies and coastlines TRIANGULATION FIGURES Construction surveys of large For a narrow triangulation system, a chain extents of figures is used TRIANGULATION SYSTEM Single Triangle Series of joined or overlapping triangles Polygons Occasional line is measured Quadrilaterals Balance of sides are calculated from angles Combination at vertices System for a wide area – figures are irregularly overlapping GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS CHAIN OF TRIANGLES 2. Approximate Method Simplest form Simple and convenient to use Not the most accurate – lack of checks Geometric consistency is attained Used in long and narrow surveys of low Not recommended for the precision adjustment of precise triangulation Only one (1) route to compute for the networks distances in the chain In chain of triangles, it is composed CHAIN OF POLYGONS of two steps: Central – point figure Station adjustment Group of triangles bounded by 3 or more Figure adjustment sides at a common vertex (station) QUADRILATERAL : APPROXIMATE METHOD Used when control is in a wide area Compute for the error of closures (li) of Skewed figure may be strengthened using the three overlapping triangles an extra diagonal Compute for the corresponding corrections CHAIN OF QUADRILATERALS (vi) for each observed angle Most commonly used Do side adjustments to determine final For long and narrow surveys of high adjusted angles using log sine precision GEODETIC TRAVERSE Each figure – 2 pairs of overlapping Carried out where in those sections of the triangles country topographic conditions make it Distribution of angular errors impracticable to carry out primary Allows point position computation by four (4) geodetic control by triangulation, independent routes for checking trilateration or GNSS methods. CHOICE OF FIGURE The condition which make it more desirable Ideal Shapes: to carry on precise traverse than primary Triangle: Equilateral triangulation are the flatness of the land and Quadrilateral: Square presence of timber. High accuracy: Ideal shapes and Must be equal in accuracy to primary recommended distance angles geodetic control Distance angles: angles opposite the Under these conditions it is necessary to known and required sides of the triangle have shorter lines Recommended Range: 30 to 150 Control system consisting of connected long degrees lines whose azimuths and distances are Recommended Value: 90 degrees measured and by the use of the geodetic formulas, the latitude and longitude of each point are computed. Lines are long enough that the earth’s curvature is considered in determining the back azimuth of a line GEODETIC TRAVERSE PROCEDURE 1. Reconnaissance 2. Angle Measurements 3. Measurement of traverse lines (Distance measurements) TRIANGULATION ADJUSTMENT METHODS 4. Position computation and adjustment ADJUSTMENT METHODS ORGANIZATION OF PARTY (TRADITIONAL) 1. Least Squares Method USGS required the following sub-parties to Most commonly used in surveying execute the different operations in geodetic and geodesy traverse It seeks the “least” sum of squares 1. Building Party of the residuals 2. Taping Party Uses the angle and side condition 3. Leveling Party equations as inputs to the 4. Check-Taping Party adjustment process 5. Angle Party Rigorous, complex and requires lengthy computations GE 414 - Geodetic Surveying Reign Dy | BSGEODENG - 3102 | MIDTERMS GEODETIC TRAVERSE 3. Length measurements, standard error Start at a known line and end at another For the 12 measurements, standard known line of the same geodetic datum and mean error is determined and Known line – old or fixed lines with fixed the ratio of the m.s.e. To the average length, azimuth and back azimuth of the 12 measurements should be 1 End points – also fixed in latitude and part in 300,000 longitude 4. Reciprocal vertical angle observations Known lines should be within the same Elevations are checked at the geodetic datum interval of 6 to 8 stations of known Angles and distances are measured from elevations the first line to last line and from data the Benchmarks to which the stations azimuth and geographic coordinates are are connected may be outside of the computed and adjusted traverse system 5. Astronomical azimuths The number of courses between azimuth checks should be 10 to 12 Stellar observations for azimuths are required after establishing 10 to 12 lines 32 observations are required and these have to be made in 2 nights at 16 observations each Azimuth closure at azimuth check point should be within 1.5” per station or 3.0”sqrt(N). In metropolitan area, closure within 2.0” per station or 3.0”sqrt(N) 6. Position closure After azimuth adjustment the position error at the check point should be 1 part in 50,000. Azimuth error should be first distributed among the lines and the latitude and longitude of each station are computed using the geodetic formulas Difference between the carried latitude/ longitude and the fixed latitude/ longitude of the checkpoint is computed (latitude/ longitude CLASSIFICATION closure error) Based on accuracy standards REQUIREMENTS Closure Error 1. Spacing of principal stations Length of the traverse (in latitude/ longitude) Stations should be seldom less than