GEOMATICS ENGINEERING / SURVEYING

Transcription

1 1 GEOMATICS ENGINEERING / SURVEYING CHAPTER 1 Dr. Muhammad Ashraf Javid Assistant Professor Department of Civil and Environmental Engineering muhammad.javid@unizwa.edu.om

2 2 Geomatics Engineering / Surveying Credit Hours (2+1) = 3.0 Assessment policy Quizzes (10%) Assignments (10%) 2 weeks will be given for each assignment and late assignments will not be entertained for any reason. Lab. Work (20%) In-Semester exams (30%) Final exam (30%)

3 3 Course Description The course covers introduction to geomatics engineering, distance measurement, leveling, angle measurement, indirect distance measurement, topographic surveying areas and volumes, construction surveying and road curve preparation and practical.

4 4 Course Contents Introduction of Geomatics engineering Coordinate systems and scales Distance measurement Angle measurement and traversing Leveling Road curve design Area and earthworks calculation Construction and topographic surveying

5 5 Chapter 1 contents Introduction Role of surveying in civil engineering Classification of surveying Basic Principles of Surveying Coordinate systems Sources of Errors

6 6 Introduction to Geomatics Engineering Geomatics It is the discipline of gathering, storing, processing, and delivering geographic or spatial information. Surveying The discipline encompassing all methods of gathering and processing information about our physical earth and its environment. Or The art of making measurements of the relative positions of natural and manmade features on the Earth s surface, and the presentation of this information either graphically or numerically. Geodesy Geodesy is the discipline that deals with the measurements and representation of the Earth, including its gravity field, in a three-dimensional time varying space. Geodesy focus on the Earth and neglect any man-made features on it (e.g. buildings, public utilities, etc.), while surveying use the results of geodesy for positioning and mapping of these features.

7 The role of Surveying in Civil Engineering Practice Surveyors are needed: to maintain the geometric order during the construction process to provide fundamental data for the design and planning process to provide quantity control during the construction process (for example: earthwork quantities) to monitor the structure after the construction ( deformations, etc.) 7 Wrong geometry the structure is not functional! What is this? Laying them in the appropriate geometry, outstanding structures can be created!

8 The role of Surveying in Civil Engineering Practice Surveying activities during the construction process 8 Before Construction Under construction After construction Planning and data collection Setting out on each phase of construction Final (as-built) plan or map on the construction Observations in the field Processing the observations (office) Drawing maps, plans or providing numerical data Field checks of construction Providing data and services to the client Presenting documentation to the client Deformation Monitoring/ Load Tests Presenting documentation to the client

9 Plane Surveying 9 Primary Classification of Surveying According to the space involved: Relatively small areas (Generally areas < 250 Km 2 ) Surface of earth can supposed to be flat Measurements plotted represent a horizontal projection of the actual field measurements All Z dimensions are referenced to the mean surface of the earth or MSL Plane surface Plane triangle Plane angles most engineering and property surveys are classed as plane surveys, although some route surveys that cover long distances (e.g., highways and railways) will have corrections applied at regular intervals.

10 Geodetic Surveying 10 Primary Classification of Surveying Large areas Surface of the Earth can not supposed to be flat The curvature of the Earth is taken into account Curved line Spherical triangle Spherical angles Don t forget! Size does matter! Mostly used for establishing control networks, determining the size and shape of the Earth and determining the gravity field of the Earth.

11 11 Secondary Classification of Surveying Based on instruments. Based on methods Triangulation surveying Traverse surveying Based on object Geological surveying Mine surveying Archeological surveying Military surveying Based on nature of field Land surveying Marine surveying Astronomical surveying

12 12 Secondary Classification of Surveying Types of Land Surveying Cadastral Surveying Boundary surveying (conducted to determine the boundaries of fields, houses) Construction Surveying Engineering surveys (done to prepare detailed drawings of projects) Topographic Surveying Ground-based mapping (done to determine natural features) City Surveying Carried out to locate the premises, streets, water supply and sanitary systems Hydrographic Surveying Involving water bodies Geodetic Surveying Locating points in space Photogrammetric Surveying Aerial surveys

13 Surveying Classification Topographical Survey Topographical survey is concerned with the measurement of natural and artificial features of the earth s surface in order that a map of these features may be drawn and printed. The methods are similar to geodetic methods but are carried out to a lower order of accuracy. Cadastral Surveying It is the process of defining, demarcating, measuring and recording the boundaries of properties. Where these boundaries are formed by physical features, it overlaps with topographical surveying. As a general rule, cadastral work is done at larger scales than topographical mapping Engineering or Construction Surveys Engineering Surveys are those conducted with the special object of supplying particular information for engineering projects. They are usually at larger scales than topographical maps, but the methods used are often similar. Sometimes a high order of accuracy is required, for example, the measuring of a gap for a bridge. 13

14 14 Basic Principles of Surveying 1. To work from whole to the part Whole area is first enclosed by main stations (i.e. controlling stations) and main survey lines (i.e. controlling lines) Then area is divided into parts by forming well-conditioned triangles Main survey lines are measured very accurately and then the sides of the triangles are measured. Main purpose is to avoid accumulation of error in measurements. 2. To locate a new station by at least two measurements (linear or angular) from fixed reference points. Linear measurements refer to horizontal distances Angular measurements refer to the magnetic bearing or horizontal angle

15 Basic Principles of Surveying 15

16 16 Basic Principles of Surveying Recall the definition of Surveying: The art of making measurements of the relative positions of natural and man-made features on the Earth s surface, and the presentation of this information either graphically or numerically. How to achieve this? Let s determine the position (X P, Y P ) of point P! The positioning is usually separated into horizontal (2D) and vertical (1D) positioning. Nowadays 3D positioning can be achieved using satellite techniques, too. Absolute vs Relative positioning Y X P P d AP Y P d BP B (X B,Y B ) Control points (known coords; marked on the field) A (X A,Y A ) l AB X

17 17 Basic Principles of Surveying Let s determine the position of a third, unknown point (P). We have two unknowns: X P, Y P We need two measurements: b two distances a Y one distance and an angle two angles P d BP a a d AP d AP b B (X B,Y B ) A (X A,Y A ) X

18 18 Basic Principles of Surveying Unknown point Unknown point Unknown point b C C C L AC? L BC? L AC? θ 1? θ 2? θ 1? A B A B A B Known length AB Known length AB Known length AB Fig. 1 Fig. 2 Fig. 3

19 19 Triangulation It is one of the methods of providing control in an area which is to be surveyed It is based on the Trigonometric proposition that if one side and three angles of a Triangle are known, the remaining sides can be computed by the application of Sine-Rule i.e.

20 20 Base Line AB is measured. Internal angles at A, B, C are measured. C D A B

21 21 Traverse A traverse consists of a connected series of lines on earths surface, the length and bearings of which have been determined. Following measurements are made:- a. Horizontal Angles b. Vertical Angles c. Distances d. Bearings Traverse Legs E D Traverse Stations A C

22 22 Trilateration Trilateration methods involve the determination of locations of controls points by measurement of distances, using the geometry of triangles. In contrast to triangulation it does not involve the measurement of angles. c a d b

23 How to create a countrywide coordinate system? In order to use the relative positioning, a proper number of control points are needed. These points: are coordinated points; are marked. 23

24 Control Networks 24 Why is it necessary to have a common countrywide coordinate system? Many engineering tasks cover a large area (highways, bridges, tunnels, channels, land registry, etc.), where the common coordinate system (reference system) should be available. The Control Network provide us with control points given in the same refence system (coordinate system). Thus measuring the relative positions of unknown points using these control points, the coordinates of the new points can be computed in the same reference system.

25 One of the Ground Control Points Established with Promark 3 for Mapping Project 25

26 26 Coordinate Systems-Basics Basic elements of a coordinate system an origin, then the location of every other point can be stated in terms of a defined direction and a distance in the direction

27 27 Coordinate Systems - Basics Coordinate System can be 2D or 3D Types of coordinate systems (1) Geographic coordinates (f, l, z) (2) Global Cartesian coordinates (x, y, z): A system for the whole earth (3) Projected coordinates (x, y, z) on a local area of the earth s surface The z-coordinate in (2) and (3) is defined geometrically, and in (1) the z-coordinate is defined gravitationally.

28 28 Coordinate Systems-Basics The most widely used global coordinate system consists of lines of geographic latitude (phi) and longitude (lambda). Lines of equal latitude are called parallels. They form circles on the surface of the ellipsoid. Lines of equal longitude are called meridians and they form ellipses (meridian ellipses) on the ellipsoid The equator is the largest circle and divides the earth in half. The prime meridian is the line of longitude that passes through Greenwich England and defines the origin (zero degrees) for longitude coordinates.

29 Coordinate 29 Systems-Basics The latitude (f) of a point P is the angle between the ellipsoidal normal through P and the equatorial plane. Latitude is zero on the equator (f = 0 ), and increases towards the two poles to maximum values of f = +90 (90 N) at the North Pole and f = - 90 (90 S) at the South Pole. z The longitude (λ) is the angle between prime meridian ellipse and the meridian ellipse containing the point P. It is measured in the equatorial plane from the meridian of Greenwich (λ = 0 ) either eastwards through λ = (180 E) or westwards through λ = (180 W).

30 30 Coordinate Systems-Basics

31 Coordinate Systems-Basics

32 32 3D Geographic coordinates (f, l, z) 3D geographic coordinates (f, l, z) are obtained by introducing the ellipsoidal height z to the system. The ellipsoidal height (z) of a point is the vertical distance of the point in question above the ellipsoid. It is measured in distance units along the ellipsoidal normal from the point to the ellipsoid surface. z 3D geographic coordinates can be used to define a position on the surface of the Earth (point P in figure).

33 Angle Vs Distances on surface of earth At equator Circumference of earth=40, kilometers Angle cover in circle=360 o Therefore; 1 degree represents approximately 111 km

34 34 3D Cartesian coordinates/ Geocentric coordinates An alternative method of defining a 3D position on the surface of the Earth is by means of geocentric coordinates (x,y, z), also known as 3D Cartesian coordinates. The system has its origin at the masscentre of the Earth with the X- and Y- axes in the plane of the equator. The X-axis passes through the meridian of Greenwich, and the Z-axis coincides with the Earth's axis of rotation. The three axes are mutually orthogonal and form a right-handed system. Geocentric coordinates can be used to define a position on the surface of the Earth (point P in figure).

35 Projected Coordinate Systems A map projection is the systematic transformation of locations on the earth (latitude/longitude) to planar coordinates The basis for this transformation is the geographic coordinate system (which references a datum) Map projections are designed for specific purposes Flat Map Cartesian coordinates: x,y (Easting & Northing) Curved Earth Geographic coordinates: f, l (Latitude & Longitude)

36 The proportion which the distance between any two points on map bears to the horizontal distance between the same two points on the ground. Scale

37 Methods of Expressing Scale IN WORDS Words explain the distance on map that represents a certain distance on ground. e.g 1 Inch or 1 cm =1 Mile etc. BY REPRESENTATIVE FRACTION The distance on map is represented by a fraction of corresponding distance on ground. e.g 1:50,000, 1/10,000 etc. BY SCALE LINE By drawing a scale line showing the digits or parts for measuring distance on the map.

38 38 Errors in Measurements Errors in measurements Sources of errors Natural causes Instrumental imperfections Personal limitations Types of errors Systematic or cumulative Systematic errors can be calculated and proper corrections are applied to the observation. Accidental, random or compensating

39 39 Precision and Accuracy of Measurements True value of a quantity is never known Accuracy is the closeness or nearness of the measurements to the true value of quantity being measured. Precision (or repeatability) refers to the closeness with which the measurements agree with each other.