Fundamentals of Surveying (LE/ESSE ) Lecture 10

Transcription

1 Fundamentals of Surveying (LE/ESSE ) Lecture 10 Topographic Mapping Dr.-Ing. Jianguo Wang Geomatics Engineering York University Fall

2 10-1 Introduction Two main types of maps: Line maps Orthophotographic image maps This lecture focus on The characteristics and construction of topographic maps in conventional line and digital formats Methods for representing relief This lecture covers Datum for Mapping Reference Coordinate Systems for Mapping Representation of Relief Contours and Contour Lines Types of topographic maps Topographic Data Collection, Processing and Plotting Map scales, accuracy Topographic Map Symbols 2

3 10-1 Introduction History Some of the earliest known maps were made in Mesopotamnia, in the area now known as Iraq, where a series of maps showing property boundaries were drawn in about 2400 B.C. for the purpose of land taxation. A Roman map dating from about A.D. showed such topographical features as roads, cities, rivers, and mountains. In 1539, the Dutch mathematician and geographer Reiner Gemma Frisius described a method for surveying an area by dividing it into triangles. This concept of triangulation became one of the basic techniques of field surveying and is still used today. One of the first large-scale mapping projects using triangulation was started in the 1670s by Giovanni Domenico Cassini, who had been persuaded to make a detailed map of France. After his death, his children and grandchildren continued to labor on the project. The final result, called the Carte de Cassini, was published in 1793 and was the first accurate topographic map of an entire country. 3

4 10-1 Introduction History The concept of contour lines to show different elevations on a map was developed by the French engineer J.L. Dupain-Triel in Although this method allowed the accurate depiction of land contours and elevations on a flat, two-dimensional map, it was not widely used until the mid-1800s. The USGS (U.S. Geological Survey) began using aerial photography techniques to produce and update maps in 1930s. In the 1980s the use of computers to scan and redraw existing maps significantly reduced the time required to update maps in areas of rapid growth. On Topographic Maps The word topography is derived from the Greek words topos, meaning a place, and graphien, meaning to write. Thus, topography is the written, or drawn, description of a place. 4

5 10-1 Introduction On Topographic Maps (cont d) A topographic map is a two-dimensional representation of a threedimensional land surface. Topographic Maps show (by using suitable symbols) 1) the spatial characteristics of the Earth s surface, with such natural features: mountains, hills, valleys, vegetation, forests, lakes, and rivers etc. 2) constructed features: cities, buildings, road, canals, bridges and cultivation etc. 3) Valuable reference information for surveyors and map makers: bench marker, base lines and meridians, magnetic declinations etc. Topographic maps are differentiated from other maps; show both the horizontal and vertical positions of the terrain the representation of the terrain relief. Topographic maps are used by civil engineers, environmental managers, urban planners, emergency services, and national defense etc. Topographic maps are geo-referenced! need for a geodetic datum, coordinate systems etc. 5

6 10-1 Introduction Products of topographic maps - the (paper) topographic maps - the orthophotos Sample Topographic Maps NTS 82O (Sample), Banff, Alberta, (1/ ) NTS 41J/2 (Sample), Blind River, Ontario (1/50 000) 6

7 10-1 Introduction Sample Topographic Maps Engineering design map prepared using CADD system [pp. 501, Elementary Surveying] 7

8 10-1 Introduction Sample Orthophotos 8

9 10-1 Introduction Samples: 3D Topographic Maps Topographic map, draped over DTM with added hill-shading. Source: Petrovič, Mašera,

10 10-1 Introduction Samples: 3D Topographic Maps 10

11 10-1 Introduction Samples: 3D Topographic Maps 11

12 10-2 Datum for Mapping 1. Datum Standards A datum defines the position of the ellipsoid relative to the center of the earth. provides a frame of reference for measuring locations on the surface of the earth by defining the origin and orientation of latitude and longitude lines. relates positions, directions and elevations measured in the field to global reference systems ( geo-referencing!). Ensures that the surveys and adjustments over a wide geographic area will be consistent with each other. Whenever you change the datum, or more correctly, the definition of the used geographic coordinate system, the coordinate values of your data will change. 2. Datum Horizontal & vertical. A country or a group of countries have maintained their own datum(s). Local datum, such as the North American Datum of 1983 (NAD 83), is designed to be used in a specific area. Datum transformations are required when survey data cross such regional boundaries with different datums. 12

13 10-2 Datum for Mapping 3. A Horizontal Datum consists of - an ellipsoid of revolution approximating the figure of the earth and - a set of constants or constraints that specify the size, position, and orientation of the ellipsoid. 4. A vertical Datum is the surface to which elevations or depths are referred. 5. Examples: Horizontal Datum 1). NAD27: The North American Datum of 1927 uses the Clarke 1866 spheroid to represent the shape of the earth. The origin of this datum is Meades Ranch in Kansas. Many NAD 1927 control points were calculated from observations taken in the 1800s. These calculations were done manually and in sections over many years. The result of this approach was errors between stations. 2). NAD83: The horizontal control datum for the United States, Canada, Mexico, and Central America - based on a geocentric origin and the Geodetic Reference System based upon both earth and satellite observations, using the GRS80 spheroid. The center of this datum is the center of the earth. - Locations between NAD27 and NAD83 shift by as much as 500 feet, however NAD 83 is compatible with GPS data - based on the adjustment of 250,000 points including 600 satellite Doppler stations which constrain the system to a geocentric origin. 13

14 10-2 Datum for Mapping 5. Examples: Horizontal Datum (cont d) 3). WGS84: the World Geodetic System of is the reference frame used by the U.S. Department of Defense (DoD) - is defined by the National Imagery and Mapping Agency (NIMA) (formerly the Defense Mapping Agency). - is used by DoD for all its mapping, charting, surveying, and navigation needs, including its GPS "broadcast" and "precise" orbits. - was defined in January 1987 using Doppler satellite surveying techniques. - was used as the reference frame for broadcast GPS Ephemerides (orbits) beginning January 23, At 0000 GMT January 2, 1994, WGS 84 was upgraded in accuracy using GPS measurements. The formal name then became WGS 84 (G730) since the upgrade date coincided with the start of GPS Week became the reference frame for broadcast orbits on June 28, At 0000 GMT September 30, 1996 (the start of GPS Week 873), WGS 84 was redefined again and was more closely aligned with International Earth Rotation Service (IERS) Terrestrial Reference Frame (ITRF) is now formally called WGS 84 (G873). WGS 84 (G873) was adopted as the reference frame for broadcast orbits on January 29,

15 10-2 Datum for Mapping 6. Examples: Vertical Datum 1). CGVD28: Canadian Geodetic Vertical Datum of the previous official Canadian height system - System has become obsolete, a new system underway. - The adoption of a new vertical datum for Canada could be as early as The only viable alternative (long-term) for Canada is a geoid model - would define the datum in relation to an ellipsoid, making it compatible with space-based technologies for positioning 2). CGVD2013 in Canada The current official Canadian height system A Geoid-based vertical datum released in 2013, defined by the equipotential surface ( W 0 = ,0m 2 s 2 ), which represents by convention the coastal mean sea level for North America. This definition comes from an agreement between the United States of America and Canada. This new vertical datum is realized by the geoid model CGG2013, which provides the separation between the GRS80 ellipsoid and the above described surface in NAD83(CSRS) reference frame, making it compatible with Global Navigation Satellite Systems (GNSS) such as GPS. 15

16 10-3 Reference Coordinate Systems for Mapping Two types of coordinate systems be used to locate features on the earth 1. Geographic coordinate system defines locations using latitude and longitude on a spherical model of the earth: the ellipsoid (includes angular unit of measure, central meridian, datum) Horizontal Datum in Surveying For example: NAD83 in north America WGS84 2. Projected coordinate system Being used by GPS defines locations as x, y (or Easting, Northing) coordinates identified on a grid using a mathematical conversion from latitude and longitude (includes unit of measure, an equally spaced grid, origin at the center x = 0, y = 0) For example: UTM 6 degree zones worldwide (UTM Grids) MTM 3 degree zones FACTS: i). On the same datums (NAD83 & CGVD2013), inclusive of heights ii). A different form of coordinates 16

17 10-4 Representation of Relief - relief models - 3D perspective views with wire frame - shaded rendering or draped imagery - contour lines - cross sections, profiles, hachures or form lines Hachures Automatically plotted contours Three-dimensional perspective terrain model 17

18 10-5 Contours and Contour Lines 1. A contour: an imaginary line of constant elevation on the ground surface. 2. Contour interval: the fixed vertical distance between successive contours representing elevation difference on a given map - depends on map scale, the degree of relief and user s needs 3. Contours and relief 18

19 10-5 Contours and Contour Lines 3. Contours and relief (cont d) 19

20 10-5 Contours and Contour Lines 3. Contours and relief (cont d) The Characteristics of Contour lines: a. All of the points on the same contour line have the identical height; b. All contour lines must close on themselves either within or outside the border of the map; c. No contour lines with different elevations cannot merge or cross one another on the map unless a steep cliff or a steep chute is reached; d. A contour line is perpendicular to the lines of steepest slope, such as the mountain ridge lines, ravine(valley) lines; e. The horizontal distance between contour lines is inversely proportional to slope. The larger slop one has in an area, the more closely spaced contour lines one will see there. The contour lines are spaced uniformly on uniform slopes. 20

21 10-5 Contours and Contour Lines 4. Types of Contour lines 1) The intermediate contour line is drawn based on the contour interval, the basic contour line; 2) The index contour line is drawn thicker than the intermediate one after 4 intermediate lines; 3) The supplementary contour line is drawn every half contour interval as user s needs. 21

22 10-6 Information shown on maps General information for any map: 1) The direction of the meridian and basis for directions. 2) A graphical scale of the map and a corresponding note stating the scale at which the map was produced. 3) A legend or key to symbols other than the conventional ones. 4) An appropriate title. 5) A statement of the contour interval on topographic maps. 6) A statement giving the datums to which horizontal and vertical control referenced. 7) A statement giving the map projection, together with the projection parameters in cases where they are not widely known. 8) A statement giving the coordinate system for which grid lines or grid ticks are shown on the map. 9) The date on which the map was produced, and the dates of any revisions. 10) A statement about the source of data used to compile the map, and the date of acquisition of such source data. 11) A sketch showing the location of the map sheet in a series of sheets covering a project area or municipal region. Some other information: (e.g.) a map as a public record of land division should have Surveyor s certification and registration number etc. 22

23 10-6 Information shown on maps 23

24 10-7 Mapping Scales, Contour intervals and Accuracies 1. Classification of topographic maps - Large scale: 1:10,000 and over (1:500, 1:1000, 1:2000, 1:5000, 1:10,000) E.g.: Ontario Digital Topographic Database: 1:10,000 - Medium scale: 1:100,000 ~ 1:25,000 (e.g.: 1:25,000, 1:50,000, 1:100,000) E.g.: National Topographic System (NTS) of Canada: 1:50,000, 100km 2 /sheet Ontario Digital Topographic Database: 1:20,000 - Small scale: 1:200,000 and smaller (1:200,000; 1:250,000; 1:500,000; 1:1000,000) E.g.: NTS: 1:250,000, 16 sheets of NTS 1:50, Contour intervals 24

25 10-7 Mapping Scales, Contour intervals and Accuracies 2. Contour intervals 25

26 10-7 Mapping Scales, Contour intervals and Accuracies 3. Accuracy of a topographic map - General rule: The distance on the ground corresponding to the visual resolution of human eyes: 0.1mm on maps (hard copy of maps). Scale accuracy of large scale mapping Map scale 1:500 1:1000 1:2000 1:5000 1:10,000 Scale accuracy [cm] cm (map)/km (ground) General Instructions for Surveys, Chapter D13 BASEMAPPING Canada Centre for Cadastral Management, Recommended Scale 1:1,000 1:2,000 1:5,000 1:10,000 1:20,000 Accuracy Requirement [m] Application dependent! 26

27 10-7 Mapping Scales, Contour intervals and Accuracies 3. Accuracy of a topographic map (cont d) - NMAS (National Map Accuracy Standards): Horizontal accuracy: no more than 10% of well-defined points be in error by more than 0.8mm at published map scale. Well-defined points: those that are easily visible or recoverable on the ground those that can be plotted at the map scale to within 0.25mm. For example: map scale 1:20,000 16m as horizontal accuracy tolerance Vertical accuracy: no more than 10% of elevations shall be in error by more than one-half the published contour interval. - Standards for large scale maps: uses the root mean square error (rms) MSE MSE Planimetric coordinate accuracy for well-defined points; class I maps Map scale 1:50 1:100 1:500 1:1000 1:2000 1:4000 1:5000 1:10,000 Planimetric limiting RMS (X or Y) [m] [( x τ ) n [( y τ ) = n x y 2 2 ] = x, y the measured coordinates from the maps ] τ the known value of x or y of checkpoints n the number of points tested

28 10-8 Topographic Data Collection, Processing and Plotting 1. Data collection Main one is photogrammetry direct field survey for small projects: total station and GPS 2. Computer-aided drafting and design 3. GIS and digital mapping 4. Data processing Design of map layout selection of map projection manipulation of map data selection of features preparation of collar information border, titles, scales, legends, graticules labels of features preparation of manuscript 28

29 10-9 Topographic Map Symbols 1. Standards and Specifications for Polychrome Maps NTS Symbols are defined based on this standard! ( 29

30 10-9 Topographic Map Symbols 30

31 10-9 Topographic Map Symbols 31

32 10-9 Topographic Map Symbols 32

33 10-9 Topographic Map Symbols 2. The USGS Symbols 3. Topographic Symbols (page 494, Surveying Theory and Practice) 33

34 10-10 Further Topics 1. Canada NTS Grid Map (homework). 2. Ontario Digital Topographic Database (homework) 3. Digital Terrain Models 4. Photogrammetric Mapping 5. GIS 6. Cadastral Mapping 34