longitude, latitude and datums
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Longitude, Latitude AndDatums
T.Ch.Hanuman Rao
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World co-ordinate system
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The World Geodetic System, CoordinateSystems, & Projections
Geographic: 38 41' 08.73" N 07708 08.37" W
Cartesian: X= 1,109,928m Y= -4,860,097m Z= 3,965,162m
UTM: 18 314251mE 4284069mN
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Horizontal Datum - A base reference for a
coordinate system. It includes the latitude andlongitude and orientation of an initial point oforigin of an ellipsoid that models the surface ofthe earth in the region of interest.
Horizontal Datum
Prime
Meridian
X
Z
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Satellite Observations of the Earth
European Remote Sensing satellite, ERS-1 from 780Km
ERS-1 depicts the eart
shape without water an
clouds. This image loo
a sloppily pealed potat
a smoothly shaped ellSatellite Geodesy has
enabled earth scienet
gain an accurate estim
(+/- 10cm) of the geoce
center of the of the earA worldwide horizontal da
requires an accurate estimof the earths center
C t f D t
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Components of Datums
WGS-84 Ellipsoid
Semi-major Axis: a= 6371837 m
Semi-minor Axis: b= 6356752.3142
Flattening Ratio: f=(a-b)/a = 1/298.257223563
Rotate Ellipse in 3Dimensions:
The Ellipsoid
a
b
H i t l D t
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Horizontal Datums
Global replaces regional datums with a common,accurate standard
One system for maps of the entire planet
Regional vs. Global Approach
D D S t llit D i d H i t l D t
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DoDsSatellite Derived Horizontal Datum
NIMAs (National Imagery And Mapping Agency World Geodetic System)
World Geodetic System 1984
Z
PrimeMeridian
X
Y
WGS -84 is an EarthCentered Earth Fixed
Cartesian coordinate
system with its origin
fixed to +/- 10 cm.
An ellipsoid is placedon top of the axis to
create a geodetic
foundation for various
coordinate systems.
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Impact of Datum Mismatch
Map dated 1989
WGS-84
Map dated 1957
NAD-27 (North American Datum 1
15S WN443015S WC4330
Impact of Datum Mismatch
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Impact of Datum Mismatch
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Gravity - Fitting the Ellipsoidto the Physical Earth
Deviation ofthe verticalEllipsoid Normal,Perpendicular to
Ellipsoid Surface
Geoid VerticalPerpendicular to
Geoid Surface
Earth Surface
Geoid:
Surface of Equal
Gravitational
Potential
Ellipsoid
Geoid Separation
Deviation ofthe vertical
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Coordinate Systems
Cartesian Coordinates:X= 1,109,928m Y= -4,860,097m Z= 3,965,162m
Geographic:
DD 38.684N, 077.150W
DM 38 41.145' N, 077 08.135 W
DMS 38 41' 08.73" N, 077 08 08.37" W
GEOREF: GJNJ5141
UTM:
18 314,251mE 4,284,069mN
C C S
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Cartesian Coordinate Systems
Three dimensional right hand coordinate system with aorigin at the center of the earth and the X axis orientedat the Prime Meridian and the Z at the North Pole
X Axis Coordinate Distance from the Y-Zplane measured parallel to the X-Axis;
Y Axis Coordinate Perpendicular distancefrom the plane of the prime meridian;positive in the eastern hemisphereand negative in the western.
Z Axis Coordinate Perpendicular distancefrom the plane of the equator;positive in the northern Hemispherenegative in the southern
Z
PrimeMeridian
X
0 Long
(X,Y
Geographic Coordinates
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Geographic Coordinates Latitude & Longitude are
defined by the Prime Meridianand the Equatorial referenceplanes
Geographic latitude Verticalangle from the equator to thenormal of ellipsoid, positivein Northern Hemisphere andnegative in the southern
Geographic longitude Horizontalangle from the prime meridian
positive in the easternhemisphere and negative in thewestern
Geodetic height Distance normalfrom the reference el lipso id
Ob
Me
PrimeMeridian
Lo
Z
X3841 08.73 N 077
08.37 W
G hi C di t
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Geographic Coordinates
Rules of thumb for latitude 1 latitude 60 nautical miles 1 latitude 1 nautical mile
1 latitude 30 meters .1 latitude 3 meters . 01latitude 30 centimeters
Dont forget longitude converges
Dont forget the base 60 conversion
60 minutes per degree 60 seconds per minute
Geographic Reference System GEOREF
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Geographic Reference System, GEOREF
0
origin 180
90N
90S
origin 180
E
0Greenwich
The earth is divided into 288 quadrangles, each 15Ox 15O, identified by an u
combination of two characters.
N
015
In the matrix, quadrangle NK is placed over the Netherlands.
M
L
J
H
G
F
E
D
C
B
A
A B C D E F G H J K L M P Q R S T U V W X Y Z
K60N
45N
M t j ti
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Mercator projection is a cylindrical map projection presented by
the Flemish geographer and cartographerGerardusMercator, in 1569.
became the standard map projection for nauticalpurposes because of its ability to represent lines of
constant course, known as rhumb lines or loxodromes, as straightsegments.
( In navigation, a rhumb line (or loxodrome) is aline crossing all meridians of longitude at thesame angle, i.e. a path derived from a definedinitial bearing.
That is, upon taking an initial bearing, one
proceeds along the same bearing, withoutchanging the direction as measured relative totrue north.)
While the linear scale is equal in all directionsaround any point, thus preserving the angles andthe shapes of small objects (which makes theprojection conformal), the Mercator projectiondistorts the size and shape of large objects, as thescale increases from the Equator to the poles, whereit becomes infinite.
How to choose projections
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How to choose projections
Generally, follow the lead of people who make maps ofarea you are interested in. Look at maps!
State plane is a common projection for all states in theUSA
UTM is commonly used and is a good choice when theeast-west width of area does not cross zone boundarie
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UTM zones
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UTM zones
Universal Tranverse Mercator
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Universal Tranverse Mercator
India UTM Zones
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India UTM Zones
U i l T M G id
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Universal Transverse Mercator Grid
2 3 4 5 6 7 8
2 3 4 5 6 7 816o
Zone 2 Zone 3156
168o174o
Central
Meridian
Zone 4162o
0o
1,700,000
1,600,000
1,500,000
1,400,000
1,300,000
1,200,000
1,100,000
1,000,000
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
03 508,256mE 0,567,359mN
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Equal ARC Standard Projection
Problem: How to make raster data square and seamless over large area
ARC Projection shrinks lower latitude pixels and stretches higher latitude pixsquare data
Problems printing small scale charts (JNC/GNC) Must re-project ARC data to get around problem
Original
Chart to bescanned
Scanning
Process Digital Chart inARC projection
Up to 12%
Shrink
12%Stretch