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Transcript of Date: 13/03/2015 Training Reference: 2015 GIS_01 Document Reference: 2015GIS_01/PPT/L2 Issue:...
![Page 1: Date: 13/03/2015 Training Reference: 2015 GIS_01 Document Reference: 2015GIS_01/PPT/L2 Issue: 2015/L2/1/V1 Addis Ababa, Ethiopia GIS Coordinate Systems.](https://reader036.fdocuments.us/reader036/viewer/2022062600/5a4d1b3f7f8b9ab0599a0389/html5/thumbnails/1.jpg)
Date: 13/03/2015Training Reference: 2015 GIS_01
Document Reference: 2015GIS_01/PPT/L2Issue: 2015/L2/1/V1
Addis Ababa, Ethiopia
GIS
Coordinate Systems
Instructor: G. Parodi
Implementation of the Training Strategy of the Monitoring for Environment and Security in Africa
(MESA) Programme
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Name Responsibility
Contribution from Gabriel Parodi Lecturer ITC, University of Twente
Edited by Tesfaye Korme Team Leader and Training Manager, Particip GmbH
Reviewed by Martin Gayer Project Manager, Particip GmbH
Approved by Robert Brown Technical Development Specialist (TDS), TAT
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GIS Trainer: Mr. Gabriel ParodiDepartment of Water Resources, Geo-Information Science and Earth Observation (ITC) at the University of Twente, Enschede, The Netherlands.
MESA Training Contractor: Particip-ITC-VITO Consortium
Consortium partners
Particip GmbHwww.particip.deMartin Gayer: [email protected]
ITC – Faculty of Geo-Information Science and Earth Observationwww.itc.nlChris Mannaerts: [email protected]
VITO – Remote Sensing Unit Applications Teamwww.vito.beSven Gilliams: [email protected]
Particip is the main Contractor
Short Introduction
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Spatial referencing
(a) International Terrestrial Reference System: ITRS (b) International Terrestrial Reference Frame: ITRF
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Two spatial referencing systems
Geographical coordinates Cartesian coordinates
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Reference surfaces: Geoid & Ellipsoid
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The Vertical datum : The Geoid
To describe height we need a imaginary zero surface. A surface where water doesn’t flow is a good
candidate. Geoid: Level surface that most closely approximates all
Earth’s oceans. Main ocean level was recorded locally, so there are
many parallel “vertical datums”.
Exaggerated illustrationof the geoid
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Vertical datums
Altitudes (heights) are measured from the vertical datums Mean sea level (geoid) Different countries, different vertical datums. E.g.: MSLBelgium - 2.34 m = MSLNetherlands
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Ellipsoids and horizontal datums
To describe the horizontal coordinates we also need a reference. To “project” coordinates in the plane we need a mathematical representation. The
geoid is only a physical model. The oblate ellipsoid is the simplest model that fits the Earth (also oblate spheroid) The ellipsoid is selected to fit the best mean local sea level. Then the ellipsoid is positioned and oriented with respect to the local mean sea level
by adopting a latitude, a longitude and a height of a fundamental point and an azimuth to an additional point.
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Horizontal datums
Datum: ellipsoid with its location. The ellipsoid positions are modified by the datums.One datum is built for one ellipsoid, but one ellipsoid can be used by several datums!
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Datum shifts (1)
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Datum shifts (2)
Care: A wrong datum and you miss the point!!
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Ellipsoid
semi-major axis
sem
i-min
or
axis
equatorialplane
Pole Mathematically describable rotational surface
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Commonly used ellipsoids
Name Date a (m) b (m) UseEverest 1830 6377276 6356079 India, Burma, Sri Lanka
Bessel 1841 6377397 6356079 Central Europe, Chile,Indonesia
Airy 1849 6377563 6356257 Great brittainClarke 1866 6378206 6356584 North America, PhilippinesClarke 1880 6378249 6356515 France, Africa (parts)Helmert 1907 6378200 6256818 Africa (parts)International(or Hayford)
1924 6378388 6356912 World
Krasovsky 1940 6378245 6356863 Russia, Eastern EuropeGRS80 1980 6378137 6356752 North AmericaWGS84 1984 6378137 6356752 World (GPS measurements)
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Datum transformations
It is mathematically straightforward.
It is a 3D transformation 3 origin shifts 3 rotation angles 1 scale factor
Δy
Δx
Δα
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Translations (3 Parameters)
Movement of points along an Axis
X
Z
Y
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Rotations (3 Parameters)
Movement of points around an Axis
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Scale (1 Parameter)
Changing the distance between points
S
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7 Parameters
XYZ
S Rxyz+
X’Y’Z’
=XYZ
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3 Parameters
XYZ
+XYZ
X’Y’Z’
=
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Classes of map projections
A map projection is a mathematical described technique of how to represent curved planet’s surface on a flat map.
There’s no way to flatten out a pseudo-spherical surface without stretching more some areas than others: compromising errors.
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Secant projections
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A transverse and an oblique projection
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Azimuthal projection
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Cylindrical projection
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Conic projection
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Properties of projections
Conformality Shapes/angles are correctly represented (locally)
Equivalence ( or equal-area )Areas are correctly represented
EquidistanceDistances from 1 or 2 points or along certain lines
are correctly represented
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Conformal projection
Shapes and angles are correctly presented (locally). This example is a cylindrical projection.
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Equivalent map projection
Areas are correctly represented. This example is a cylindrical projection.
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Equidistant map projection
Distances starting one or two points, or along selected lines are correctly represented. This example is a cylindrical projection.
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Compromise projection (Robinson)
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Principle of changing from one into another projection
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Comparison of projections (an example)
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Universal Transverse Mercator: The UTM coordinate system
Transverse cylindrical projection: the cylinder is tangent along meridians
60 zones of 6 degrees Zone 1 starts at longitude 180° (in the Pacific
Ocean) Polar zones are not mapped X coordinates – six digits (usually) Y coordinates – seven digits (usually)
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UTM-Zones
0oEquator
Central M
eridian
Greenw
ich
0o 6o
…. 29 30 31 32 …..
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Two adjacent UTM zones
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Classification of map projections
Class• Azimuthal• Cylindrical• Conical
Aspect• Normal• Oblique• Transverse
Property• Equivalent (or equal-area)• Equidistant• Conformal• Compromise
Secant or Tangent projection plane
( Inventor )
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