Longitude, Latitude and Datums

8/12/2019 Longitude, Latitude and Datums

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Longitude, Latitude AndDatums

T.Ch.Hanuman Rao


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World co-ordinate system
http://localhost/var/www/apps/conversion/tmp/scratch_5/Dimensions_1_English.mov


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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



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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

Longitude, Latitude and Datums

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