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
When the Earth Was Flat Measurements were made using a plumb bob, a spirit level, and a stick. Also, the Stars.
What is The Shape of the Earth? Flat Spheroid Ellipsoid
What to Do with Errors and Blunders? Can we eliminate blunders? Can we eliminate errors? Can we reduce errors? How?
The Geoid Source: atlas.geo.cornell.edu/ people/weldon/earth-3d.gif
A Point as Center for Earth (Peter H. Dana, 1994)
The geoid, ellipsoid, spheroid, and the topographic surface.
The ellipsoids of Clark 1880 and WGS84
The Two Dimensional Earth and Map Projections Example: Cylindrical Mercator projection 180 W 00 180 E 80 N 80 N 10 N 00 10 S The Equator 10 N 00 10 S Legend The Region of Least Distortion 80 S 80 S 180 W 00 180 E
A Universal Transverse Mercator Zone
A sample Satellite Map UTM Vs. Geographic (Lat./Lon.)
USA, UAE Geoid Elevation: Approximately 10 to 20 meters above datum
So what is the problem? Traditional survey measure geoid height (Orthometric). GPS survey measure ellipsoidal height. Which one do want to use?
GIS Easy to transform location data Hard to accept discrepancies and errors How GIS perceive errors? Question: What is the acceptable error?
GPS Ground Control Points: Surveying Methods (Traditional) GPS Technology (Accuracy +/- 5 meters) DGPS (High Accuracy) Spatial Statistics
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 57 51 and 57 55.3333 54.00 Lat. of origin 0 0 0 0 False Eastings 500,000 500,000 500,000 500,000 False Northings 0 0 0 0 Scale factor 0.9996 0.9996 1.0000 0.9995
Current Projection Systems used at the UAE DLTM (Central Meridian 55 20 ) UTM zone 39 (Central Meridian 51 ) UTM zone 40 (Central Meridian 57 ) 51 52 53 54 Iran 55 56 57 Bahrain Qatar : United Arab Emirates Oman Saudi Arabia 51 52 53 54 55 56 ERWDA Standards (Central Meridian 54 ) 57
The scale factor UTM zone 40 North
Example of three projections used in the UAE
Landsat TM image of the area with point location in the three cities
Latitude, longitude, and distance between the three selected points Longitude Decimal D. Latitude Decimal D. Distance Meters Abu Dhabi 54.3571550 24.4851800 Al Ain 55.7383450 24.2320770 142921.897 Dubai 55.3215000 25.1507972 110161.784 122233.211
The calculated Eastings and Northings Using Different Programs Program 1 Program 2 Differences City Name Eastings Northings Eastings Northings Eastings Northings Abu Dhabi 232148.000 2710505.966 232148.141 2710505.176-0.141 0.790 Al Ain 371899.978 2680500.013 371899.962 2680499.260 0.016 0.753 Dubai 330814.799 2782698.907 330814.852 2782698.035-0.053 0.872 Note: All measurements are in meters.
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 232148.000 2710505.966 Al Ain 371899.978 2680500.013 142936.953 142921.897 15.056 Al Ain 371899.978 2680500.013 Dubai 330814.799 2782698.907 110148.109 110161.784-13.675 Dubai 330814.799 2782698.907 Abu Dhabi 232148.000 2710505.966 122257.753 122233.211 24.542 Clarke 1880 zone 40N Abu Dhabi 232145.805 2710545.371 Al Ain 371898.905 2680538.989 142938.141 142921.897 16.244 Al Ain 371898.905 2680538.989 Dubai 330813.495 2782738.750 110149.000 110161.784-12.784 Dubai 330813.495 2782738.750 Abu Dhabi 232145.805 2710545.371 122258.730 122233.211 25.519
Continue From Previous Eastings Northings Distance Datum Distance Difference DLTM Abu Dhabi 401044.897 2709377.435 Al Ain 541136.644 2681053.154 142926.424 142921.897 4.527 Al Ain 541136.644 2681053.154 Dubai 498806.886 2782758.635 110162.667 110161.784 0.883 Dubai 498806.886 2782758.635 Abu Dhabi 401044.897 2709377.435 122238.320 122233.211 5.109 ERWDA Abu Dhabi 536201.955 2708939.349 Al Ain 676570.301 2681959.027 142937.785 142921.897 15.888 Al Ain 676570.301 2681959.027 Dubai 633243.196 2783272.553 110189.240 110161.784 27.456 Dubai 633243.196 2783272.553 Abu Dhabi 536201.955 2708939.349 122239.224 122233.211 6.013 Note: All measurements are in meters. Distances were calculated using Pythagoras theory.
Distance and transformation of DLTM coordinate to UTM WGS84 zone 40 at the Street Level DLTM Eastings DLTM Northings UTM Eastings UTM Northings Point 1 500000 2800000 332221.5647 2799923.299 Point 2 500100 2800000 332321.5517 2799922.056 Distance between points 100 99.99474149 Difference between - measurements 100-99.9947414893429 = 0.005258511 Note: All measurements are in meters. Distances were calculated using Pythagoras theory.
In Louisiana State Plane Coordinate System Based on 1927 USA datum. Modified 1983. Lambert (Conical). Designed to remain constant. NAD83 Zone 1701 North NAD83 Zone 1702 South Note: Earth shape (Spherical VS Ellipsoidal)?
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.
State Plane VS UTM
Differences in projections NAD83 Zone 1701 N. NAD83 Zone 1072 S UTM WGS84 Zone 15
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.?????