When the Earth Was Flat. Measurements were made using a plumb bob, a spirit level, and a stick. Also, the Stars.

Transcription

1

2 ABSTRACT Defining the shape of the Earth geoid. Mathematical models spheroid or ellipsoid Mathematical projection of geodetic systems GIS/GPS technology The need for a unified projection systems World Wide. The United Arab Emirates (UAE) UTM WGS84, UTM Clark 1880, ERWDA Standards, and Dubai Local Transverse Mercator (DLTM). In Louisiana NAD83, UTM WGS84. Potential problems and errors The need of a unified projection system

3 When the Earth Was Flat Measurements were made using a plumb bob, a spirit level, and a stick. Also, the Stars.

4 What is The Shape of the Earth? Flat Spheroid Ellipsoid

5 What to Do with Errors and Blunders? Can we eliminate blunders? Can we eliminate errors? Can we reduce errors? How?

6 The Geoid Source: atlas.geo.cornell.edu/ people/weldon/earth-3d.gif

7 A Point as Center for Earth (Peter H. Dana, 1994)

8 The geoid, ellipsoid, spheroid, and the topographic surface.

9 The ellipsoids of Clark 1880 and WGS84

10 The Two Dimensional Earth and Map Projections Example: Cylindrical Mercator projection 180 W E 80 N 80 N 10 N S The Equator 10 N S Legend The Region of Least Distortion 80 S 80 S 180 W E

11 A Universal Transverse Mercator Zone

12 A sample Satellite Map UTM Vs. Geographic (Lat./Lon.)

13 USA, UAE Geoid Elevation: Approximately 10 to 20 meters above datum

14 So what is the problem? Traditional survey measure geoid height (Orthometric). GPS survey measure ellipsoidal height. Which one do want to use?

15 GIS Easy to transform location data Hard to accept discrepancies and errors How GIS perceive errors? Question: What is the acceptable error?

16 GPS Ground Control Points: Surveying Methods (Traditional) GPS Technology (Accuracy +/- 5 meters) DGPS (High Accuracy) Spatial Statistics

17 Example: Geodetic Systems used in the UAE Name and Zone 39 Zone 39 DLTM ERWDA datum and 40 and 40 UTM WGS84 Clark 1880 WGS84 WGS84 Parameters Lon. of origin 51 and and Lat. of origin False Eastings 500, , , ,000 False Northings Scale factor

18 Current Projection Systems used at the UAE DLTM (Central Meridian ) UTM zone 39 (Central Meridian 51 ) UTM zone 40 (Central Meridian 57 ) Iran Bahrain Qatar : United Arab Emirates Oman Saudi Arabia ERWDA Standards (Central Meridian 54 ) 57

19 The scale factor UTM zone 40 North

20 Example of three projections used in the UAE

21 Landsat TM image of the area with point location in the three cities

22 Latitude, longitude, and distance between the three selected points Longitude Decimal D. Latitude Decimal D. Distance Meters Abu Dhabi Al Ain Dubai

23 The calculated Eastings and Northings Using Different Programs Program 1 Program 2 Differences City Name Eastings Northings Eastings Northings Eastings Northings Abu Dhabi Al Ain Dubai Note: All measurements are in meters.

24 Calculated Eastings, Nothings, distances, and the difference between the calculated distances on a flat surface and that of an ellipsoid surface Eastings Northings Distance Datum Distance Difference WGS84 zone 40N Abu Dhabi Al Ain Al Ain Dubai Dubai Abu Dhabi Clarke 1880 zone 40N Abu Dhabi Al Ain Al Ain Dubai Dubai Abu Dhabi

25 Continue From Previous Eastings Northings Distance Datum Distance Difference DLTM Abu Dhabi Al Ain Al Ain Dubai Dubai Abu Dhabi ERWDA Abu Dhabi Al Ain Al Ain Dubai Dubai Abu Dhabi Note: All measurements are in meters. Distances were calculated using Pythagoras theory.

26 Distance and transformation of DLTM coordinate to UTM WGS84 zone 40 at the Street Level DLTM Eastings DLTM Northings UTM Eastings UTM Northings Point Point Distance between points Difference between - measurements = Note: All measurements are in meters. Distances were calculated using Pythagoras theory.

27 In Louisiana State Plane Coordinate System Based on 1927 USA datum. Modified Lambert (Conical). Designed to remain constant. NAD83 Zone 1701 North NAD83 Zone 1702 South Note: Earth shape (Spherical VS Ellipsoidal)?

28 UTM System Based on WGS48. Transverse Mercator (Cylendrical). Global system designed with change over time UTM Zone 15 (West LA) Almost all of LA. UTM Zone 16 (East LA) Divide the Grand Isle in half.

29 State Plane VS UTM

30 Differences in projections NAD83 Zone 1701 N. NAD83 Zone 1072 S UTM WGS84 Zone 15

31 Conclusion Defining datum for Louisiana is Essential Almost the entire coast is marches (sea level) A standard map projection promotes integration and sharing information among various users. GPS/GIS Technology forces unity in standards. Example: Oil spill operation started GIS with ESRI WGS84 projection system. Dos it cost. Defiantly. Do we care.?????