principles of gis and interactions with remote sensingkmcenter.rid.go.th/kmc01/pdf/1/4/integration...

1Thaïlande, September 2001Value-added Remote Sensing Products Development for Geo-Information Systems

Principles of GIS and interactions with Remote

Sensing

Forest vegetation map from Lozere (IFN)


COURSE CONTENT :

? Introduction

? The concepts of Geographic Information Systems

? The modelisation of the geographic information

? The Sources of data and acquisition methods

? The main functions of a GIS

? The complementarity between GIS and Remote Sensing

? Future prospects of remote sensing products and GIS implications


Introduction :

•Remote sensing development due to public sector (first Landsat MSS launched in 1972, first Spot 1986)•GIS development due to private sector (growth since 1980)

Today, we observe an increasing demand of data/information at scales from global to local in various fields of applications

Remote sensing and GIS are linked technologies :

To be effectively analysed and employed, remote sensed datamust be combined with other data/Information

For GIS, to be most effective, they need to contain accurate and up to date data.


« A system of hardware, software, data, people, organisations and institutional arrangements for collecting, storing, analysing, and disseminating information about areas of the earth. » Dueker & Kjerne, 1989 * :

The concepts of GIS

All data are All data are georeferenced georeferenced ::Data located by means of geographical coordinateswith respects to some reference systems

A data set A data set organisedorganised

A A tool tool for for decision makingdecision making


«Real world»

Technicien(s)

Software GeographicalInformationDatabase

Data producers

Sofwareproducers

GIS products :maps, etc...

User(s)

The main componentsThe main components

•Computer hardware•Software•Data•Skilled people

The concepts of GIS


The concepts of GIS

Comprehensive GIS require a means of :

•Data input, from maps, aerial photos, satellites, surveysand other sources,

•Data storage, retrieval and query,

•Data transformation, analysis and modelling,

•Data reporting, such as maps, reports and plans.


The Modelisation of geographic information

The importance of geographic location in GISThe importance of geographic location in GIS

•Management, analysis and reporting of GIS data requires that it be carefully referenced by position on the Earth ‘s surface.

•Many different coordinate systems are used to record location :

some systems are global : latitude and longitudeother sytems are regional or local

•GIS users must be familiar with a variety of commonly used coordinate systems


For thousands of years, human beings try to draw the Ground as accurate as possible

•How to draw in 2D the real 3D world ?

First step : to know the real shape of the Earth and the way to modellize it => geodesy - definition of the geodetic system

•what is the Earth shape ?•can we find a simple geometric feature to approximate it locally ?

Second step : how to put in 2D the « simplified » shape of the Earth ? => concept of projection

The Modelisation of geographic informationQuestions raised by cartographyQuestions raised by cartography


3D real world 2D representation (1658)

The first problem : from 3D to 2D...The first problem : from 3D to 2D...



What is the Earth shape ?What is the Earth shape ?

Definition of geodesy : science to study the shape of the Earth.

In the history, 4 figures to model the Earth shape :

• the plane

• the sphere

• the ellipsoïd

• the geoïd : it is a sealevel equipotentialsurface - the surfaceon which gravity iseverywhere equal to itsstrentgh at mean sealevel. Real Earth



The ellipsoid :The ellipsoid :

Ellipsoid earth models are required for precise distance and directionmeasurement over long distance.

Reference ellipsoids are definedby either :

•semi major and semi minor axes or•the relationship between the semi-major axis and the flatenning of the ellipsoid

Many reference ellipsoids are in use by different nations and agencies

Ellipsoid name semi major axe (m) semi minor axe (m) eccentricity ²Clarke 1880 6378249 6256515 0,006803WGS 72 6378135 6356750 0,006694WGS 84 6378137 6356752 0,006694

Modelisation of geographic information


Coordinate systemsCoordinate systems

•Geographic coordinates : ( ? ,? ??h)

? longitude : the east west angular distance fromthe equator

? latitude : the north south angular distance from equator

h Distance from the reference ellipsoid to the point in adirection normal to the ellipsoid

. M •Plane coordinate system



In cartography, the geometric system is completly define by :

- the geodetic system :

•the ellipsoïd (major axis, flattening)• its orientation (three angles)• its center (three coordinates)

- the elevation system

- the projection system

In cartography, the geometric system is completly define by :

- the geodetic system :

•the ellipsoïd (major axis, flattening)• its orientation (three angles)• its center (three coordinates)

- the elevation system

- the projection system



Elevation systemsElevation systemsCareful !Two points are said to be at the same altitude if the gravity value is the same,that is water can not flow from one point to the other.The elevation is calculated above a given ellipsoïd, or above the geoïd (a model).The elevation is given in meters or feet, or ...

=> necessity to have a digital model of the geoïd



The aim is to represent the Earth surface on a plane. We have therefore to define two functions giving the planar coordinates (X and Y) from the geographic coordinates (? ,? ).

X = f (? ,? ?Y = g ?? ,? ?

The (f,g) pair is a cartographic projection

The usual projections are optimized to minimize the deformations,the f and g functions so defined are complex

PROJECTIONSPROJECTIONS



Mercator (cylindrique conforme)

Robinson (cylindrique aphylactique)

Sinusoïdale oblique équivalente

Plate carrée (cylindrique équidistante)



Different types of data

Real World

Object

Real World

Image

Raster

Attribut

Tables and Vector

Remote sensing

Image processing

Vector Raster

GIS



Two types of Geographic Information :Two types of Geographic Information :163

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? Graphical data? Graphical data

ADM_ AREA PERIMETER NOM_REGION NOM_DEP NOM_COM SURFACE STATUT_COM163 21596720.000 23016.811 MIDI-PYRENEES HAUTE-GARONNE SAINT-LYS 2159 Chef-lieu de canton175 37780352.000 34111.090 MIDI-PYRENEES HAUTE-GARONNE SAINTE-FOY-DE-PEYROLIERES 3806187 10059210.000 16869.359 MIDI-PYRENEES HAUTE-GARONNE SAINT-CLAR-DE-RIVIERE 1005190 6166357.000 11176.710 MIDI-PYRENEES HAUTE-GARONNE LAMASQUERE 616196 58468488.000 52988.180 MIDI-PYRENEES HAUTE-GARONNE MURET 5846 Chef-lieu d'arrondissemen200 8562927.000 14429.800 MIDI-PYRENEES HAUTE-GARONNE CAMBERNARD 856212 6355410.000 11372.000 MIDI-PYRENEES HAUTE-GARONNE LABASTIDETTE 635217 27646390.000 28785.900 MIDI-PYRENEES HAUTE-GARONNE LHERM 2764228 22766880.000 26151.670 MIDI-PYRENEES HAUTE-GARONNE POUCHARRAMET 2276

? Descriptive element (attribute)? Descriptive element (attribute)



Two different modelisations of geographic informationTwo different modelisations of geographic information

Information organization of graphical data


? VECTOR MODE : used to project object into a continuous space; gives a precise description

(1) Representation of forms and positionning of geographic objects

Points (or node) Surfaces (or polygons)Line (or arc)

Examples of geographic objects

•Towns• Observations,• Spring

• Roads• Rivers• Paths

• Parcels of land• Districts• Land cover



? VECTOR MODE

DESCRIPTIVE LEVEL

woodwood

roadroad

GEOMETRIC LEVEL

redred

greengreen

DRAWING

1

2

"SPAGHETTI model

Unstructured model,objects described independently

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AB

TOPOLOGICAL model

Topological relationships between objectsare described.

(2) Representation of spatial relation : TOPOLOGY (...)



? VECTOR MODE

?

? ?

?

NODE

coordinates (x,y)

??A

ARC

serie of nodes (x,y) +start node (D)and end node (A)

D

?

?

?

?

POLYGON

series of arcs +right hand polygon (R)et left hand polygon (L)

R

L

Advantages of topology : data is entered more easily and quickly(particularly surface type data, redundancy of graphic information is avoided, cartographic data can be used for analysis purposes (notion of adjacency or connectivity).

(2) Representation of spatial relation : TOPOLOGY (...)



? RASTER MODE : regular division of space into rectangular or square elements

A cover = one description ofthe territory.1,1: Origin of the image

Pixel size = resolutiondX

dY

Pixel identified by its position (raw and column number) and one attribute (value = integer real or alphanumeric)



COMPARISON RASTER / VECTORCOMPARISON RASTER / VECTOR

•Any given situation can be represented in both raster and vector modes•The choice is up to the user•Conversion from raster to vector and vice versa is possible•Computers are now able to display simultaneously vector and raster•Vector and raster are seen as complementary

Method Advantages Disadvantages

Raster ? Simple data structure? Compatible with remotelysensedor scanned data? Simple spatial analysisprocedures

? Requires greater storage space oncomputer

? Depending on pixel size, graphicaloutput may be less pleasing

? Projection transformations are moredifficult

? More difficult to represent topologicalrelationships

Vector ? Requires less disk storagespace

? Topological relationships arereadily maintained

? Graphical output moreclosely resembles hand-drawn maps

? More complex data structure? Not as compatible with remotely sensed

data? Software and hardware are often more

expensive? Some spatial analysis procedures may

be more difficult? Overlaying multiple vector maps is often

time consuming



Can be filed in several different forms depending on how it needs to be used an access :

•Flat file or spreadsheet : simplest method for storing data•Flat file or spreadsheet : simplest method for storing data

ADM_ AREA PERIMETER NOM_REGION NOM_DEP NOM_COM SURFACE STATUT_COM163 21596720,000 23016,811 MIDI-PYRENEES HAUTE-GARONNE SAINT-LYS 2159 Chef-lieu de canton175 37780352,000 34111,090 MIDI-PYRENEES HAUTE-GARONNE SAINTE-FOY-DE-PEYROLIERES 3806

•Advantage : simple structure and easy to use

•Disadvantage : adding new record is time consumingslow data retrieval without a key

Information organization of descriptive data

Descriptive dataDescriptive data


defined as an automated, formally defined and centrally controlledcollection of persistent data used and shared by different usersin an enterprise (Date, 1995)

Information organization of descriptive data

Database systemDatabase system

Different database models :

•The relational model : data are organised by records in relations whichresemble a table : the most commonly used

•The object oriented model : data are uniquely identified as individual objects that are classified into object types or classes according to the characteristics (attributes and operations) of the object.The emerging database model


DATA SOURCES AND DATA INPUT

Of the 4 components of an Information system (data, technology, process and people), data are most expensive to acquire

In many project, the collection of data accounts for half or moreof the capital investment.

The user will need to ensure that the data are compatible with hisapplication and considers :

•the accuracy of the data •the length of the record•the scale of the data•the georeferencing system used•the data collection technique and sampling strategy used•the quality of the data collected•the data classification and interpolation method used

•the accuracy of the data •the length of the record•the scale of the data•the georeferencing system used•the data collection technique and sampling strategy used•the quality of the data collected•the data classification and interpolation method used


Error, Accuracy and Precision

Data quality refers to the relative accuracy and precision of a particular GIS database

Accuracy : is the degree to which information on a map or in a digitaldatabase matches true or accepted values. Is applied to geographicposition as well as attribute, conceptual and logical accuracy.

Precision : is the level of measurement and exactness of a description in a GIS database

•The level of precision/accuracy required for particular applications varies greatly

•Highly precise and/or accurate data can be very difficult and costly to produce and compile


The different types of geographical data

Raw geographical data are available in many different analogue or digital forms :

1 2 34 5 12 16 2 1

Satellite images Aerial photographs TablesThematic or topographicmaps

They can be acquired :

•in digital form from a data supplier•in analogue form and manually digitized or scanned,•from one’s own survey of geographic entities (using GPS)


Remote sensed images can be integrated in a GIS as

An active layer : the digital data is processed (by classification, filtering, etc..) to extract information

A Passive layer :the digital data is not used, a visual interpretation allows to update or create information

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Image used visually Image classified

Remote sensed images as input in a GIS


Internet as a source of dataInternet as a source of data

A lot of data are now available on the Internet. Some of them free of charge. Not all are up to date.Main limits are speed of data transmission and access

Examples Examples •World meteological data from FAO:http://www.fao.org/WAICENT/FAOINFO/SUSTDEV/EIdirect/CLIMATE/EIsp0002.htm

•World soil map from FAO :http://www.fao.org/waicent/FaoInfo/Agricult/AGL/AGLS/T1.HTM

•Database of soils of East Africa at a scale of Base des 1:1 million (SOTER) http://www.fao.org/WAICENT/FAOINFO/SUSTDEV/ frdirect/gis/eigis000.htm

•Digital Chart of the World (world topographical data 1/1000000) http://www.maproom.psu.edu/dcw/

http://kartoserver.geog.uu.nl/html/staff/oddens/mapsatl3.htm listes more than2350 sources of digitals maps

World soil map from FAO

Source of data


Creating data sets by manual input

Satellite images

Aerial photographs

Thematics maps

Points data

Documentscanner

Correctorientation

and distortions

Digitizeboundaries and

rasterize

Interpolate

Joint rasteroverlay structure

*D’après Burrough (1998) Principles of Geographic Informations Systems


Satellite images

Aerial photographs

Thematics maps

Documentscanner

Correct orientationand distortion

Digitizebounderies

Interpolation

Interpretation

Vectorizelines and

bounderies

Joint vector overlaystructure

*D’après Burrough (1998) Principles of Geographic Informations Systems

Creating data sets by manual input

Point data


Scanners are devices for converting analogue

data into digital raster images

Acquisition

Document scannersDocument scanners

The resulting scanned image may need interactive treatment to remove excess data from the image using by thresholding or binarization

Then it may be vectorized.


DigitizersDigitizers

The aim of the digitizer is to input quickly and accurately the coordinates of points and boundary lines

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The use is time consuming and enervating work. There are manydifferent sources of errors :

•undershoot,•overshoot•no attribute•too many attribute

Acquisition


Acquisition

Topographical surveyTopographical survey

Carried out by tacheometry or Global positioning systems for :

•drawing detailed topographical maps of limited areas•establishing a framework for other data capture technique (like remote sensing or photogrammetry)


» »Each software use its own solutions to handle the geometric and topological aspects of the data (proprietary format) »

– Commercial format transfert like e00 or DXF have come to be generally– supported by the data providers.

– There is a trend in Gis community for developping OpenGIS and – interroperability. It refers to the need to create systems which support

the– efficient description, storage, access, and transfer of geographical data – throughout organizations, countries.

Conversion of existing dataConversion of existing data

Acquisition


DATA ACQUISITION

Remote SensingDigitalisationScanning

GPSFile importation

DATA MANAGEMENT

StructurationAccuracy checkingUpdate

TransformationAgreggationGeneralisationRestructurationExtraction

DATA MANIPULATION CalculationRetrievalSpatial operators

DATA ANALYSIS

Spatial analysisThematic analysis

RESTITUTION

ScreenGraphsChartsImagesMapsFiles

THE MAIN FUNCTIONS OF A GISMain functions


Manipulation and transformation of spatial data

Data layers must be in the same map projection for analysis.

Typically 20 or more different map projections are supported in a GISsoftware

Map projection transformation :Map projection transformation :


« RASTERIZATION » :loosing of information due to

pixel size

« VECTORISATION » :resulting data require much editing

Multiplication of small polygons.

polygon

arc

Restructuring : Raster/VectorRestructuring : Raster/Vector

An alternative to automated vectorisation is digitizing from the image display on the screen



?Descriptive : Combination of objects from the same classe of attribute

?Graphic : Combination of objects according to spatial criteria

»polygons connected to the

red one »

Graphic or descriptive dissolvingGraphic or descriptive dissolving



Extraction Extraction

Clipping of objects Overlapping objects Included objects

Selection according to an area of interest

•to optimize processingoperation, working on a portionof the database•to avoid immobilising the entire database

Area of interest



Interactive Graphic editingInteractive Graphic editing

Addition, deletion, moving and changing of the geographic objects for updatingor correcting errors

Deletion of all polygons whose area < 200m²



On the metric and geometric characteristics of objects : distance, perimeter area, volume :

123

number of points

Number of points by polygon

distance,length

Curve Incline

area

perimeter

Spatial measurement :Spatial measurement :

Data analysis


Example of request on attribute data

Examples of request on spatial data

Area / Perimeter >= 50Distance < 100 m.

Information retrievalInformation retrieval

Selective search, manipulation and output of data Both on spatial and attribute data

Data analysis


« Specific treatments applied on geographic information for their transformation or analysis »

Some operations are more specific to raster or vector mode

» Overlays» Buffers» Neighbourhood operations : » analysis of spatial relationship between objects» Filters (on raster images)» Network» 3D

Data analysisSpatial operationsSpatial operations


Data analysisOverlaysOverlays

•In vector mode :

-Complex operation-Creation of numerous polygons

•In vector mode :

-Complex operation-Creation of numerous polygons

•In raster mode :

-Simple operation-No creation of new objects

•In raster mode :

-Simple operation-No creation of new objects


Overlays in Vector modeOverlays in Vector mode

A

B

Polygon Attribut1A 1

Polygon Attribut2B 1

SUPERIMPOSITION

A

B

PolygonsINTERSECTION

Topology construction

C

Polygone Attribut1 Attribut2C 1 1

PolygonsUNION

A'

B'

C

Polygone Attribut1 Attribut2A' 1 0B' 0 1C 1 1

Data analysis


Criteria A Criteria B

Overlay in raster modeOverlay in raster mode

Reclassification

x =Multiplication

Booleans images :

: 1 (Yes)

: 0 (No)

Raster overlay is based on arithmetic operation :addition, substraction, division, multiplication

Data analysis


In vector mode :

• contiguity, proximity, connectivity•Network analysis

In raster mode :

•Digital elevation models and derived layers, •filters•interpolation (Transformation of discrete data into continuous ones); distance en viewshed

Data analysis

Neighbourhood operationsNeighbourhood operations

Evaluate the characteristics of an area surrounding a specific location


Buffering and corridorsBuffering and corridors

Created around point, ligne or polygon

Buffer conditionnel

In vector mode

Data analysis

Ability to create distance buffer around selected features : points, lines, polygonsor pixels. It is used in Proximity analysis or for the study of protected perimeters.

Distance image

In Raster mode

From one pixelor a group of pixels

Reclassification


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Interpolation

INTERPOLATIONINTERPOLATION

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In raster modeMethod of predicting unknown valuesusing known values of neighbouring locations

Creation of a digitalelevation model

Data analysis


Network analysisNetwork analysis

Two examples of network analysistechniques are :the allocation of values to selectedfeatures within the network

and the determination of shortestpath between connected points within the network based on attribute values (minimal distance,rate of flow, impedance, cost)

In vector mode

Route optimization

Data analysis


Displaying results for communication purposesDisplaying results for communication purposes

Maps publishing (atlas)Maps publishing (atlas) Representation of graphic data andtheir attributes

Representation of graphic data andtheir attributes

Population by district

GraphicsGraphics

Animation on screenAnimation on screen

Restitution


THE COMPLEMENTARITY OF RS AND GIS

There is an ever increasing synergy between remote sensing and geographical Information systems.

•RS can be used as a tool to gather datasets for use in a GIS

•GIS datasets can be usedas ancillary information toimprove products derived fromremote sensing


GIS Remote sensing

Using GIS data as ancillary informationUsing GIS data as ancillary information

GIS can manage useful information : relief, pedology, climatology,topography,… that can help improving the accuracy of the interpretation.

Leve

l1

: 1:

100.

000i

ème

Corine Land Cover Programme using photo-interpretation of Landsat and Spot images and ancillary data.


Using GIS data for stratificationUsing GIS data for stratification

Stratification is the technique of broadly dividing the landscape into majorareas which have different characteristics : topographic, phenological, geological or climatological in order to improve the result of thematicclassification

GIS Remote sensing


Software of image interpretation are often very poor in tools for manipulation, retrieval of information and restitution : GIS can bring those functions

GIS functions improve image valorisationGIS functions improve image valorisation

Example of integration of Satellite Imagery and GeographicInformation:THE SPACEMAP

GIS Remote sensing


Image data characteristics :

?coverage?resolution?accuracy?repeat period?spectral bands?stereoscopy

Use of images for inventoring, updating and monitoring:

?when phonomena to be mapped are locatedin poorly accessible areas?when field surveys are very expensive. ?when a global coverage is required ?to observe phenomenons in other spectral regions than the visible waveband? to get a regular information?when the phenomena have to be evaluated very quickly.

Remote sensing GIS


• Image used as a background or benchmark (spatial reference) for vector data

• Integration of digital values (vegetation index...)

• Digital thematic map (visual analysis, classification)

• Digital Elevation Model (and derived parameters : slopes, orientation)

• Continuous source of data

Integration of images into a Geographic Information System :Integration of images into a Geographic Information System :

Remote sensing GIS


Image used as backgroundImage used as background

Image can be a spatial reference and used as background.

It is particularly interestingin countries where no topographical data are available.

Remote sensing GIS


Topographic map update

(P+XS) SPOT images, 1:50,000. Survey of Kenya / IGN International

1972 edition 1994 1996 edition

Remote sensing GIS


STEREOSCOPIC IMAGES

SPOT stereoscopicview

left image right image

Digital Terrain Model

EXTRACTION OF DIGITAL TERRAIN (ELEVATION) MODELS (DTM/DEM)EXTRACTION OF DIGITAL TERRAIN (ELEVATION) MODELS (DTM/DEM)Sensors capable of acquiring with different viewing angles

( SPOT / RADARSAT)

The method of extraction of DEMs usethe effect of Parallaxdue to the views at different angles, from which the elevation is deducted

DEM = digital image

The digital count of eachpixel corresponds to itselevation or altitude

Remote sensing GIS


Area without variation

Water without variation

Erosion

Accumulation

Dynamic of the river amazone (Bernex et al.,1993)

Change detectionChange detection

Remote sensing GIS


TownArea without influencefrom the river

waterAccumulation

Erosion

Road network

1 to 6: set of soil and vegetation

1: younger6: older

123456

Map of environmental impact

IQUITOS - PERÚ

Dynamic of the river amazone (Bernex et al.,1993)

Remote sensing GIS


An example of application : Deforestation Evaluation

•to measure the rates and impacts of tropical deforestation locally,•anticipate where forest clearings are more likely to occur next.

The objectives :

The study area :The study area is located around the town of Bertouain the Eastern Province of

Cameroon.

ModelisationModelisation DeforestationDeforestation

B. Mertens, F. Lambin (1997) : Spatial modelling of deforestation in southern Cameroon

Remote sensing GIS


Landsat image1973

Landsat image1986

classification classification

Land cover map1973

Land cover map1986

GIS

Field observations

Topographicalmap Digitalisation Road network

towns

Remote sensing

GPS

Data acquisition

Remote sensing GIS


Processing and resultsProcessing and results

LAND COVER1986

LAND COVER1973

Forest areas are in green, and the areas deforested between 1973 and 1986 are highlighted in red

By subtracting reflectance measured at the two dates a change map is producedResults of the change detection analysis indicate a net reduction in forest cover area between 1973 and 1986.

The net deforestation rate (i.e. ratio between the reduction in forest cover and the forest-cover area in 1973) is 6.89%, i.e., 0.53% annually.

Remote sensing GIS


Change matrix of land cover classes between 1973 and 1986 (km²)Change matrix of land cover classes between 1973 and 1986 (km²)

1986

1973 Dense forest Savannah, bare soil and water

Agriculture

Dense forest

Savannah, bare soil and water

Agriculture

6505.33

107.37

161.06

125.27

599.53

205.81

644.27

80.53

483.20

Remote sensing GIS


Spatial Modelling

Several spatial variables were generated using standard GIS analysis tools.

?Shortest distance to the nearest road

?Shortest distance to the nearest town

?Shortest distance to the nearest forest-nonforest edge in 1973

?Spatial fragmentation of the forest cover in the immediate surroundings of each location

All these variables were integrated in a GIS and co-registered geometrically with the forest-cover change map derived from the analysis of remote sensing images.

Remote sensing GIS


Spatial projections of "deforestation risk zones"Spatial projections of "deforestation risk zones"

Remote sensing GIS


Emerging trends in the integrated analysis of RS and GIS data

•Use of very high dimensionality data from RS and GISAdvanced visualisation (Virtual reality)

•Remote environmental mappingHyperspectral techniques (imaging spectrometry)Fusion of multi sensor, multiview angle, multi-date data

•Object Analysis/Search in integrated RS and GIS datasetsIntegrated spatial and temporal representation and analysis toolsExploration tools (data mining)


T h a n k y o u f o r y o u r a t t e n t i o n …..

Myriam CHIKHIGroupement pour le Développement de la Télédétection Aéropstiale

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