Using Maps with GPS

1. Using Maps with GPS GPS for Fire Management - 2004

2. Using Maps with GPS Objectives: • Explain the purpose of datums. • Identify the two “global” coordinate systems most commonly used with GPS. • Describe “datum shift,” and the relevance it has when using GPS in the field. • Describe the four components that make up UTM coordinates. • Identify the three ways that lat/long coordinates can be expressed.

3. Projecting a Sphere Onto a Plane Three-dimensional sphere to two-dimensional flat map.

4. Examples of Several Projections Depending on the projection, a certain amount of distortion occurs when portraying the earth on paper.

5. Projections and Datums Meade Ranch (Clarke 1866)

6. Datum Shift 4790 1000m 700m 275m 4789 Datum corner NAD27 4788 543 541 542

7. Datum Shift 4790 1000m 600m 350m 4789 Datum corner NAD83 4788 543 541 542

8. Datum Shift A set of coordinates can yield different positions due to different datums. WGS72 NAD83/WGS84 NAD27 (true position) NAD27 Greenland Bermuda 1957

9. GPS Works in WGS84 & ECEF Datum Displays Coordinate System Displays The receiver’s processor always works in datum WGS84 and coordinate system ECEF. The user can only change the way coordinates are displayed by setting datum and coordinate system.

10. GPS Uses WGS84 & ECEF Datum Coordinate System Receiver’s processor always performs calculations in WGS84 and Earth Centered Earth Fixed (ECEF). User selects the datum and coordinate system for display only.

11. Maps • A map is a two-dimensional representation of the earth. • Maps incorporate projections and datums to provide a way to reference locations on the map to features on the ground (via coordinate systems). • All maps distort the earth to some extent. • Many different types of maps can be used with GPS. • When using a GPS receiver with a map, the datum and coordinate system in the receiver must match the map datum.

12. Example of a USGS Map Legend MN GN 18 1/20 00 28’ 8 MILS 329 MILS • Mapped, edited, and published by the Geological Survey • Control by USGS USC&GS • Topography from aerial photographs by multiplex methods • and by plane-table surveys 1953. Aerial photographs taken 1951 • Polyconic projection. 1927 North American Datum • 10,000 foot grid based on Idaho coordinate system, west zone • 1000-meter Universal Transverse Mercator grid ticks, • 1000-meter Universal Transverse Mercator grid ticks, zone 11, shown in blue • To place on the predicted North American Datum 1983 move the projection lines 15 meters north and 77 meters east as shown by dashed corner ticks UTM GRID AND 1971 MAGNETIC NORTH DECLINATION AT CENTER OF SHEET

13. Coordinate Systems • All coordinate systems reference some particular set of numbers for the size and shape of the earth (the datum). • Coordinate systems are used to designate locations within a datum. • There are two types of global coordinate systems: • Angular coordinate system (lat/long is one) • Rectangular (Cartesian) coordinate system (UTM is one) • Latitude and longitude, and Universal Transverse Mercator are two global coordinate systems commonly used by GPS users. • Many other coordinate systems exist worldwide.

14. Coordinate Systems hddd0 mm.mmm’: N 43040.93’ X W 1160 17.235’ (40.93’/ 60 =.682160) hddd.ddddd0 : N 43.682160 X W 116.287250 Different coordinates representing the same location: hddd0 mm’ ss.s”: N 430 40’ 55.8” X W 1160 17’ 14.1” (55.8”/ 60 =.93’) UTM/UPS: 11T 0557442m E 4836621m N

15. Latitude & Longitude

16. Latitude & Longitude • A geographic (spherical) coordinate system. • Are angular coordinates are perfectly suited to the ellipsoidal shape of the earth. • Coordinates are expressed in degrees, minutes and seconds (and variations of that). • Position coordinates are based on an angular distance from a known reference point. • That reference point is where the Prime Meridian and Equator intersect. • Lat/long is the predominant coordinate system used for nautical and aeronautical navigation.

17. Latitude & Longitude Prime Meridian (Longitude) 30º N 10º N 0º 0º 10º S Equator (Latitude) Point of Origin

18. Latitude & Longitude N Prime Meridian 30º 20º 10º 30º E 10º W 30º 20º 10º 20º + 10º 20º 0º, 0º Equator 30º S

19. Latitude • Latitude is comprised of parallels, which are equally spaced circles around the earth paralleling the Equator. • Parallels are designated by their angle north or south of the Equator (10º, 20º, etc) . • The Equator is 0º latitude, and the north and south poles are at 90º angles from the Equator. • The linear distance between parallel (latitude) lines never changes, regardless of their position on the earth.

20. Parallels of Latitude 20º N 10º N 10º 690 miles 0º N 10º 690 miles 10º S 10º 690 miles

21. Longitude • Longitude is comprised of meridians that form one-half of a circle, or plane. • Meridians are designated by their angle west or east of the prime meridian. • The prime meridian is designated 0º and extends from the north pole to the south pole through Greenwich, England. • Meridians are angled, and do not parallel each other. • The linear distance between one degree of longitude at the Equator is approximately 69 statute miles. • The linear distance between one degree of longitude at the arctic circle is only about 26 statute miles.

22. Meridians of Longitude 10º To North Pole 240 mi 10º 460 miles Equator 10º 690 miles To South Pole 110º W 120º W

23. Determining Latitude & Longitude Prime Meridian (0º) 30º N Equator (0º) 30ºN, 50ºW 50º W

24. Determining Latitude 17’ 30” LatitudeLine 2.5 min Latitude of red square = 44º 16’ 30” L A T I T U D E 44º 15’ 00” LatitudeLine LONGITUDE 7.5 min. scale 1:24,000

25. Determining Longitude L A T I T U D E MeridianLine LONGITUDE 7.5 min. scale 1:24,000 MeridianLine 2.5 min 115º 17’ 30” 20’ Longitude of red square = 115º 19’ 00”

26. Universal Transverse Mercator • Is a rectangular (planar) coordinate system based on the latitude and longitude (geographic) coordinate system. • The earth is divided into 60 UTM zones. • Sixty zones allows the earth to be projected onto maps with minimal distortion. • UTM uses “false” values (easting and northing) to express coordinates. • Coordinates are expressed in meters.

27. UTM Coordinates UTM Zone Number Easting Coordinate UTM Latitude Band Letter Northing Coordinate 11T0541450 4789650

28. UTM Coordinates 10,000 meter digit 1,000 meter digits 100,000 meter digit(s) 05 47 4 8 1450 9650 11T You need only plot the black numbers on the map. The rest of the coordinate values are provided for you by the map.

29. UTM Grid Overlay 21 84º N X W V U T T S R 21 T Q P Latitude Bands N M L K J H G F E D C 80º S 60 Zones, and 20 Latitude Bands Zones 1 60 Equator

30. UTM Zones in the Contiguous U.S. Longitude 1260 1200 1080 1020 840 780 1140 960 900 660 720 19 10 11 12 18 13 17 16 14 15 UTM Zones

31. UTM Zones - Side by Side 840 N 60 60 60 60 60 60 Equator 800 S Zones: 11 12 13 14 15 16

32. Increasing 4791 4790 x Increasing 543 542 y UTM Uses a Cartesian Grid

33. 9 5 0 5 4789 541 9 Place the corner of the UTM grid reader on the point to be plotted 1,000 m 4791 Plotting UTM Coordinates UTM grid reader 4790 543 542 Each tic = 100 meters on this grid reader (yourgrid reader has 20 meter tics) House coordinates = 0541450mE 4789650mN

34. A Final WordPrecision vs Accuracy • Precision and accuracy are not the same. • Precision refers to how small an area coordinates can be defined or plotted. • GPS lat/long coordinates can be defined to 1/10 of a second. • UTM coordinates can be defined down to one meter. • Accuracy refers to how closely a GPS receiver can calculate its position relative to its true location. • GPS accuracy can vary from a few millimeters to several kilometers.

35. Using GPS with Maps Objectives revisited: • Explain the purpose of a datum. • Identify the two “global” coordinate systems most commonly used with GPS. • Describe “datum shift,” and the relevance it has when using GPS in the field. • Describe the four components that make up UTM coordinates. • Identify the three ways that lat/long coordinates can be expressed.