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 thetopographic surface.

The ellipsoids of Clark 1880 and WGS84

The Two Dimensional Earth and Map ProjectionsExample: Cylindrical Mercator projection

80 S180 W 00 180 E

80 S

80 N180 W 00 180 E

80 N

The Equator10 N0010 S

10 N00

10 S

The Region of Least Distortion

Legend

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?

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

Spatial Statistics

GPS

Example:Geodetic Systems used in the UAE

Name and Zone 39 Zone 39 DLTM ERWDAdatum and 40 and 40UTM WGS84 Clark 1880 WGS84 WGS84Parameters

Lon. of origin 51 and 57 51 and 57 55.3333 54.00Lat. of origin 0 0 0 0False Eastings 500,000 500,000 500,000 500,000False Northings 0 0 0 0Scale factor 0.9996 0.9996 1.0000 0.9995

Current Projection Systems used at the UAE

51°

51°

52°

52°

53°

53°

54°

54°

55°

55°

56°

56°

57°

57°

United Arab EmiratesOman

Saudi Arabia

Qatar

Bahrain

Iran

ERWDA Standards (Central Meridian 54°)

UTM zone 40 (Central Meridian 57°)UTM zone 39 (Central Meridian 51°)DLTM (Central Meridian 55°20’)

:

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

LongitudeDecimal D.

LatitudeDecimal D.

DistanceMeters

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 SystemBased 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 SystemBased 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 SUTM 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 ……. ?????