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Spatial data management

CHAPTER 4


In the previous chapter you have seen how spatial data is entered in ILWIS via

digiti ing! Another "ethod #or o$taining spatial data is to convert digital data intoother #ile #or"ats! So"eti"es% you o$tain data that "ight not $e directly usa$le in ananalysis! The data "ay still need to $e edited! The data "ay $e in the wrong data type#or a speci#ic type o# analysis! &ou "ay have to convert data #ro" one vector type toanother 'e!g! #ro" seg"ents to polygons(% or #ro" vector to raster 'rasteri ation(! The

data "ay also contain the wrong coordinates% geore#erence% do"ain or representation!

In this chapter the various spatial data "anage"ent operations are shown% which precede the actual data analysis! The #irst part o# this chapter 'section 4!)( deals withthe i"port o# raster and vector "aps #ro" di##erent #ile #or"ats! In section 4!*% thetopic o# "ap pro+ections is treated% and how you can change "aps #ro" one pro+ectionto another! In section 4!,% tools #or vector data "anage"ent are shown% and in section4!4% the vector to raster conversion is de"onstrated! Then in section 4!-% the tools #orthe "anage"ent o# raster "aps are e.plained!

The #inal section 4!/ #ocuses on the conversion o# do"ains!

ILWIS 3.0 Users Guide 1

0ou$le1clic2 the ILWIS icon on the des2top!

3se the avigator to go to directory the C56ILWIS ,!7 0ata63sers 8uide6Chapter74 !

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9e#ore you can start with the e.ercises% you should start ILWIS and change to thesu$directory C56ILWIS ,!7 0ata63sers 8uide6Chapter74 % where the data #iles #or this chapterare stored!

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4.1 Importing digital data

In the previous chapter you have seen how to digiti e "aps! However% so"eti"es"aps "ay already $e availa$le in digital #or"at #ro" another source! They "ay have

$een generated using di##erent so#tware% they "ay have resulted #ro" scanning "aps%or they "ay $e availa$le as digital satellite i"ages or scanned i"ages! In order to usethese digital data in ILWIS% the #iles need to $e i"ported to the ILWIS #ile #or"atsthat are re:uired! I"porting can $e done with the I"port "odule% in which you canselect the i"port "ethod and #or"at!

While i"porting #iles into ILWIS% you "ust 2now what type o# data you arei"porting5 whether it is a point% seg"ent% polygon or raster "ap% and what type o#in#or"ation is stored inside the "ap! The content o# a "ap deter"ines the do"ain type'class% I0% value% i"age% picture% color% etc!( that will $e assigned to the i"ported "ap!

Within ILWIS% you can use the nor"al ILWIS i"port% $ut you can also i"porte.ternal #iles via 8eo8ateway!

GeoGateway is a product o# PCI 8eo"atics 'http5;;www!pcigeo"atics!co"( whichallows progra"s to access data in "any geo"atics #ile #or"ats% in a uni#or" "anner%

without having to translate the" $e#ore use in applications! 8eo8ateway includesaccess to i"agery% vectors% attri$utes% pro+ections and other au.iliary in#or"ation o#interest to users o# geo"atics applications!

When using 8eo8ateway% you can choose to51 per#or" a genuine import and translate the e.ternal #ile to an ILWIS #or"at5

1 the e.ternal data will $e translated into ILWIS #ile #or"ats5 ILWIS o$+ectde#inition #iles 'e!g! !

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A#ter you used I"port via 8eo8ateway % you will o$tain an ILWIS object collection !The o$+ect collection contains the ILWIS o$+ects that are the result o# the i"port! &oucan open an o$+ect collection $y dou$le1clic2ing it in a Catalog = you can su$se:uentlyopen the i"ported o$+ects also $y dou$le1clic2ing!

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4.1.1 Importing raster data through ILWIS importRaster "aps can $e i"ported #ro" a nu"$er o# #ile #or"ats! So"e o# these #or"ats donot allow the storage o# coordinates! This is the case #or the #re:uently used #ileinterchange #or"ats5 Tag I"age >ile 'TI>( #or"at% and the Windows 9it"ap '9 #ile #or"at is #re:uently used as the storage type #or scanned i"ages! Herean e.a"ple is shown o# i"porting a scanned aerial photograph o# the city o#Cocha$a"$a!

As you can see the i"port o# $lac2 and white TI>> i"ages% results in an i"age


>ro" the >ile "enu o# the !

Select the #ile5 Airphoto!ti#% leave the ?utput >ilena"e as it is andclic2 ?@ ! The "ap Airphoto is now i"ported!

?pen the raster "ap Airphoto and chec2 that it doesn t have coordinates!

>ro" the >ile "enu o# the "ap window% select Properties % and ) "apAirphoto! The Properties sheet is opened!

>ro" the >ile "enu o# the

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Spatial data managementdo"ain #or the output "ap!

When you i"port a TI>> i"age% the do"ain o# the i"ported i"age depends on thestorage type o# the TI>> #ile! ILWIS can i"port raster data with ) $it;pi.el 'intodo"ain $it(% 4 or $its;pi.el 'into do"ain i"age(% 4 or $its;pi.el with a colorloo2up ta$le 'into do"ain picture(% up to *4 $its per pi.el 'R89% into do"ain color(!The sa"e is true #or #iles that are in Windows $it"ap #or"at '!9

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?ther #ile #or"ats% such as the ER0AS !8IS %ER0AS !LA and I0RISI !0?C;!I

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In the ne.t e.ercise you will i"port an I@? ?S i"age with a ) "eter resolution! Asthis #ile is al"ost 7

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4.1.3 Importing through General "aster Import

I"port 8eneral Raster is designed to i"port raster "ap #or"ats which are not directlysupported $y ILWIS nor $y 8eo8ateway! >iles to $e i"ported "ay have a $andse:uential structure% a $and interleaved structure or a pi.el interleaved structure!

This option does not auto"atically read the header line o# the #ile that nor"allycontains in#or"ation a$out the "apFs di"ensions% coordinates% data type% etc!The user is as2ed to enter re:uired in#or"ation "anually% there#ore you should have

so"e 2nowledge a$out the header si e and the structure o# the #ile!

In this e.ercise% a glo$al ,7 Arc Second Elevation 0ata #ile will $e i"ported which is part o# a glo$al 0igital Elevation ro" the >ile "enu o# the or"at list $o.% leave the ?utput >ilena"e as it is% clear the chec2 $o.Co"$ine co"pati$le vector layers % and "a2e sure that the chec2 $o.Convert to ILWIS data #or"at is cleared!

Clic2 ?@ ! The I2onosBCocha$a"$a!ti# #ile is now i"ported!

0ou$le1clic2 the o$+ect collection I2onosBCocha$a"$a! The o$+ectcollection is opened!

0ou$le1clic2 the "ap list in the o$+ect collection and clic2 the ?pen AsColorCo"posite $utton! The 0isplay ?ptions

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Spatial data managementavaila$le on the ILWIS C01R?< and the ILWIS we$ site!

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I# you would li2e to edit the contents o# the "ap% you need to convert the data #ile toILWIS data #or"at! In this case% you will not edit the "ap nor use it in anothere.ercise! There#ore it is su##icient to use the data #ile in the original #ile #or"at!


E.pand the I"port;E.port ite" in the ?peration1tree % and dou$le1clic2I"port 8eneral Raster ! The I"port dialog $o. is opened!

Select the #ile5 W)77S)7!0E

or"at list $o.!

Accept the ?utput >ilena"eW)77S)7 and clic2 ?@ ! The I"port 8eneralRaster dialog $o. is opened!

Type 7 #or Header Si e !

Select ) #or u"$er o# 9ands !

Type 4 77 #or u"$er o# Colu"ns !

Select Integer nu"$ers #or Pi.el Structure !

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The "ap window shows part o# the continent o# South A"erica! The i"ported "aphas syste" do"ain value! When "oving the "ouse pointer in the "ap window% youwill see that the "ap has no coordinates! 9e#ore you can use this i"ported "aptogether with other data in ILWIS% you need to create a geore#erence #or the "ap!

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Raster "ap W)77S)7 is now displayed with the proper coordinates and can $e usedin co"$ination with other data in ILWIS!

ote that pi.els in the ocean area have a value % which indicates that there isno data availa$le% while in ILWIS this should $e unde#ined! &ou can correct the "apwith a #or"at!

The conversion #ro" ArcIn#o !E77 #or"at depends on the contents o# the #ile% and willILWIS 3.0 Users Guide 1

Type #or

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Spatial data managementeither result in a seg"ent "ap% possi$ly with a point "ap containing polygonla$els% or a polygon "ap! The do"ain will always $e identi#ier!

In this e.ercise% you will i"port an ArcIn#o !E77 #ile which contains the entire drainagenetwor2 o# 9olivia! The #ile% 0nnet!E77% is part o# the 0igital Chart o# the World andhas $een downloaded #ro" the 0igital Chart o# the World Server at Penn State3niversity Li$raries at http5;;www!"aproo"!psu!edu;dcw! The i"port will result inan ILWIS seg"ent "ap and an attri$ute ta$le!

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The conversion #ro" AutoCad !0O> "ay $e a seg"ent "ap% a polygon "ap and;or a point "ap% depending on the contents o# the #ile! I# the codes in the !0O> #ile onlycontain nu"erical values 'as is the case #or contour lines(% the output do"ain will $evalue! ?therwise it will $e a class do"ain 'i# there is "ore than ) code(!

In this e.a"ple a "ap o# South A"erica% in AutoCad !0O> #or"at 'Sa"erica(% will $ei"ported as a polygon "ap with a class do"ain! ote that in this case each polygonhas a separate $oundary line% without topology!


>ro" the >ile "enu o# the ile "enu o# the !

Select the #ile5 Sa"erica!d.#! Leave the >ilena"e as it is and clic2 ?@ !The "ap Sa"erica is now i"ported!

?pen the Properties sheet o# the polygon "ap Sa"erica% and change thecoordinate syste" to LatLon! The coordinates in this "ap are geographicalcoordinates!

0isplay the polygon "ap Sa"erica% chec2 the coordinates and the na"es

ILWIS 3.0 User s Guide124

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4.1.% Importing #e$tor data through GeoGate a!

E.ternal vector #ile #or"ats can $e i"ported using the nor"al ILWIS I"port % $ut youcan also i"port vector #iles through 8eo8ateway% which supports "any current vector#ile #or"ats! The result o# a 8eo8ateway i"port is an ILWIS o$+ect collection!

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>or "ore in#or"ation on the i"port o# vector and raster data% see the ILWIS Help !

Summar!& Importing data

1 Raster "aps can $e i"ported #ro" a nu"$er o# #ile #or"ats! So"e o# these #or"atsdo not allow #or the storage o# coordinates% #or instance the Windows 9it"ap'!9ile #or"at '! TI>( only stores coordinates when it has

$een e.ported as 8eoTI>> ! ?ther #ile #or"ats% such as the ER0AS !8IS% ER0AS !LA %and the I0RISI !0?C;!Iile "enu o# the or"at list $o. and leave the ?utput >ilena"e as it is!

Clear the chec2 $o. Co"$ine co"pati$le vector layers and clic2 ?@ !The Cocha$a"$a!pi. #ile is now i"ported!

0ou$le1clic2 the o$+ect collection Cocha$a"$a! The o$+ect collection isopened!

?pen the "ap list and clic2 the ?pen As ColorCo"posite $utton! The0isplay ?ptions

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Spatial data managementdirectly supported $y ILWIS nor $y 8eo8ateway! >iles to $e i"ported "ay have a

$and se:uential% a $and interleaved% or a pi.el interleaved structure!

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4.2 'ap pro(e$tions

The "aps that you o$tain a#ter i"porting% o#ten need to $e changed $e#ore you canuse the" in co"$ination with the rest o# your data! The di##erent tools that you canuse to change vector and raster "aps will $e e.plained in the rest o# this chapter! ?neo# the "ost i"portant changes that "ay have to $e done is related to the coordinateso# the "ap! The "ap "ay not have coordinates 'in the case o# raster "aps i"ported#ro" TI>> or 9

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Spatial data managementrevolving an ellipse around its "inor a.is(!

A spheroid has * di##erent se"i1a.es a and b% where a is the radius o# the e:uatorcircle and b is the hal# a.is o# rotation ' b Q a(! See >igure 4!)9!

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The #lattening o# the ellipsoid is de#ined $y5# 'a1$(;a

and the eccentricity5 e e 'a a 1 $ $( ; a a

It #ollows that the ellipsoid shape is also co"pletely de#ined $y a and f or $y a and e! early , o# the earth s land sur#ace is "apped using only #our o# these ellipsoids5International% @rassovs2y% 9essel and Clar2e ') 7(! Ta$le 4!) lists the ellipsoidsavaila$le in ILWIS! They are stored in te.t #ile Ellips!de#! In this #ile% #or each ellipsethe value o# a 'e:uatorial radius( and 1/f 'the inverse o# the #lattening( are listed!

I# no ellipsoid is 2nown% the choice $y de#ault is a sphere with a $ /,J)77J "!

The choice o# the ellipsoid% which #its $est a given region o# the earth s sur#ace to $e"apped% depends on the sur#ace curvature and geoid undulations in that region!Hence every country has its own $estN ellipsoid! See also the ILWIS Help topic SelectEllipsoid !

+a,le 4.1& Re#erence ellipsoids% which can $e chosen in ILWIS!

Airy ) ,7 >ischer ) /7ATS JJ >ischer ) /

Australian ational 8RS 79essel ) 4) Hel"ert ) /79essel ) 4) ' apan $y Law( Hough ) /79essel ) 4) ' a"i$ia( Indonesian ) J4Clar2e ) // International ) *4Clar2e ) 7 @rassovs2y ) 47Clar2e ) 7 'I8 ( '?r$its( ischer ) /7Everest 'India ) ,7( ew International ) /JEverest 'India ) -/( S8S -Everest '

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igure 4!*(! The possi$ility o# asecant cone is also present in this class! The outline o# the world would $e #anshaped!

Pro+ections can also $e su$divided according to their aspect 5 The direction in which acylinder% plane or cone is oriented with respect to the glo$e! In >igure 4!* two

possi$ilities are given5 or"al and transverse aspects! >or cylindrical pro+ections anormal aspect is a cylinder that touches the e:uator! A transverse aspect is a cylinderthat touches the poles! Si"ilarly the nor"al and transverse aspects o# a i"uthal

pro+ections can $e visuali ed! The aspect "ay also $e oblique = in that case thecylinder% plane or cone is not hori ontally or vertically oriented% $ut so"ething in

)igure 4.2& Cylindrical% a i"uthal and conical pro+ections! >or each pro+ection a tangent 'touch1ing the glo$e(% and a secant 'intersecting the glo$e( version is shown! The lower right parto# the #igure illustrates two aspects5 or"al 'oriented parallel to the earth s a.is( andtransversal 'oriented perpendicular to the earth s a.is(

ILWIS 3.0 User s Guide128

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Spatial data management $etween!


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Another i"portant way to su$divide "ap pro+ections is according to their properties !As "entioned $e#ore% a "ap pro+ection always results in so"e de#or"ation ordistortion! 0epending on the type o# pro+ection% these distortions will $e di##erent!

This is indicated $y the so1called special properties! The "ost i"portant propertiesare5 1 Conformality 5 A con#or"al "ap is one in which all angles are indicatedcorrectly!

All angles "easured on the earth s sur#ace are "easured with the sa"e values inthe "ap! As all angles are "aintained% the shape o# the o$+ects is also preserved!

1 quivalence 5 A "ap with an e:uivalence property is called an equal!area map !Although the shape o# o$+ects is distorted% the area as "easured on the glo$e iscorrectly indicated on the "ap!

1 quidistance 5 An e:uidistant "ap has the characteristic that along a special set o#lines% distances are e:ual!

ile "enu% choose Properties and select theseg"ent "ap World! Chec2 the coordinate syste" on the Seg"ent

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ow the e##ect o# several "ap pro+ections on the display o# the world "ap will $ede"onstrated! >or each pro+ection a new coordinate syste" should $e created!


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The Coordinate Syste" dialog $o. now displays "ore in#or"ation% relevant #or this pro+ection! The central cylindrical uses the e:uatorial radius o# the earth% since thecylinder touches the earth at the e:uator! See >igure 4!*!

The false easting % false northing and central meridian are used to de#ine the O% &coordinates o# the "ap! "alse easting 5 ?verall increase o# "ap .1coordinates' eastings (% indicating the eastward shi#t o# the origin o# the pro+ection relative to therede#ined origin 'negative i# pro+ection origin is west o# #alse origin(! "alse northing 5?verall increase o# "ap y1coordinates ' northings (% indicating the northward shi#t o#the origin o# the pro+ection relative to the rede#ined origin 'negative i# pro+ectionorigin is south o# #alse origin(! We won t change the" now!

Clic2 the Pro+ection $utton!

Select the pro+ection5 Central Cylindrical and clic2 ?@ !

Type so"e positive values #or

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Spatial data managementThe "ap you see is neither con#or"al nor e:ual area! It is pro+ected perspectively#ro" the center o# the earth onto a cylinder tangent to the e:uator 'see >igure 4!*(!The e:uator and other parallels are straight lines 'spacing increases towards the poles(and "eet "eridians 'e:ually spaced straight lines( at right angles! Parallel spacingincreases towards the poles! The poles cannot $e shown! Scale is true along thee:uator! Shape% area and scale distortion increases rapidly away #ro" the e:uator!This "ap pro+ection only shows the areas surrounding the e:uator correctly! All otherareas are too "uch distorted!


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+a,le 4.2& So"e o# the pro+ections availa$le in ILWIS! See #or other pro+ections and descriptions also the ILWISHelp topics Select pro+ection and Suggested pro+ections!

-ro(e$t ion "emar s

/!lindri$al

Cassini

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Spatial data management8no"onic

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+a,le 4.2 continued5

-ro(e$tion "emar s

Stereographic Apparently invented $y Hipparchus '*nd century $c(! 3sed in co"$ination with 3T< pro+ec1tion as 3niversal Polar Stereographic '3PS( #or "apping poles and in navigation charts #or latitudesa$ove 7K! Reco""ended #or con#or"al "apping o# regions that are appro.i"ate1ly circular in shape!

>or e.a"ple% used #or topographic "aps o# the etherlands!

3PS 3niversal Polar Stereographic! A i"uthal and perspective pro+ection! urther widely

used #or topographic "aps!

Polyconic or A"erican Polyconic 'Hassler% ) *7(!

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Spatial data managementDan der 8rinten Shows the entire earth within one circle! All areas% shapes and angles are greatly distorted!

&ou will see that the world is pro+ected in a circular way on a plane which touches theearth at 7 degrees latitude and longitude! There#ore% the e:uator and the 7 degrees"eridian are straight lines!


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ow the pro+ection is such that the plane touches South A"erica! The e:uator is nolonger a straight line! ?nly the /7K W "eridian is now a straight line!

ow the e##ect o# a conical pro+ection will $e de"onstrated!

Create another coordinate syste"5 La"$ertBCC! Select the pro+ection5La"$ert Con#or"al Conic!

Type so"e positive nu"$ers #or

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ow only the area surrounding the orth Pole is displayed% in a very distorted way!

The Southern He"isphere is now shown in a conical pro+ection!

So"e pro+ections will also $e shown that are use#ul #or displaying world "aps!

The world "ap is now displayed as i# you loo2 at the earth #ro" space!

&ou will now see the continent o# Asia!


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3p to now you have only seen the di##erent pro+ections displayed on the screen! Toactually trans#or" the "ap% you need to use the Trans#or" Seg"ent operation in thiscase% since the "ap world is a seg"ent "ap! >or points you use the Trans#or" Points %and #or polygons the Trans#or" Polygons operation! They wor2 $asically the sa"e!

+he U+' pro(e$tion

There is one "ap pro+ection that will $e treated in "ore detail% which is the pro+ection used "ost in 8IS and i"age processing #or relatively s"all study areas!The Universal #ransverse $ercator ' U#$ ( pro+ection syste" was developed in the

See the e##ect o# the Plate Carree% the

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Spatial data managementlate ) 47s $y the 3S Ar"y! Since then% it has $eco"e a standard in topographic"apping! The 3T< co"prises the #ollowing #eatures51 The pro+ection is the 8auss1 @rVgerN version o# the Transverse

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1 The origin o# each one is located on a point at the e:uator% where it is intersected $y the central "eridian o# that one!

1 The Easting o# the origin o# each one is assigned a value -77%777 "!

1 Each one has its own coordinate syste"!1 The 3T< has a special convention #or recording the orthings! >or the Southern

He"isphere the e:uator is assigned the value )7%777%777! >or the orthern

He"isphere the value at the e:uator is assigned as 7!1 The 3T< "ight use one o# the #ollowing de#initions o# the shape o# the earth5

International Spheroid% Clar2e ) // 'A#rica(% Clar2e ) 7 ' orth A"erica(%Everest or 9essel '$oth #or s"aller parts o# Southern and South East Asia(!

?ne o# the o$+ections to the introduction o# the 3T< "ap pro+ection% was the "ethodo# dividing the world into /7 ones! A country was li2ely to $e divided into several3T< ones% each having its own coordinate de#inition and origin! Still the 3Tor each output pi.el the total nu"$er o# points respectively the totallength o# seg"ents is calculated! >or "ore in#or"ation% see the ILWIS Help topicRasteri e !

Summar!& e$tor to "aster $on#ersion

1 Conversion #ro" vector to raster #or"at 'rasteri ation( is o#ten a necessary step preceding data analysis!

1 Points% seg"ents and polygons are represented $y grid cells 'pi.els( in the rasterdata structure!

1 In order to convert a "ap #ro" vector into raster #or"at% a "esh with pre1de#inedcell si e is positioned over the "ap! The si e o# the grid cells is a crucial aspect o#the raster data structure!

1 9e#ore starting the rasteri ation% a geore#erence should $e created! A geore#erencecontains the "ini"u" and "a.i"u" O and & coordinates o# the raster "ap% thenu"$er o# rows and colu"ns and the pi.el si e!

#or the ?utput Raster

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4.% "aster data management

A raster "ap can $e o$tained either via rasteri ing a vector "ap% as was e.plained inthe previous e.ercise% or #ro" i"porting raster data% as was shown in section 4!)! Anu"$er o# tools are availa$le to adapt raster "aps #or the analysis! In order to $e a$leto use raster "aps o# the sa"e area together% all "aps should have the sa"e pi.el si e%and the sa"e nu"$er o# rows and colu"ns! In this section a nu"$er o# tools #or"anipulating raster "aps will $e shown% such as the creation o# a su$ "ap% co"$iningtwo raster "aps into one "ap% "irroring and rotating "aps% resa"pling "aps% editingraster "aps% and the conversion #ro" raster to vector!

/reating a su, map o a raster map

The sub map operation allows you to speci#y a rectangular part o# a raster "ap andcopy it into a new raster "ap! &ou can speci#y corners either in row and colu"nnu"$ers or in O&1coordinates! A raster "ap with any type o# do"ain can $e used asinput! The output "ap uses the sa"e do"ain as the input "ap! The operationauto"atically creates a new geore#erence #or the output "ap! This operation is veryuse#ul #or creating su$scenes #ro" an entire #ra"e o# a satellite i"age% only coveringthe area o# interest!

In this e.ercise% a selected window o# a hillshading "ap o# a part o# South A"erica'Hillshad( will $e saved as a new raster "ap 'HillshadBsu$(! We also have a "ap

9oliviaB"as2% containing only the country o# 9olivia! >ro" this i"age the area thatILWIS 3.0 Users Guide 1

?pen the "ap 9oliviaB"as2% and #ind out the area that should $e e.tract1ed 'e.pressed in #irst line% #irst colu"n% nr! o# lines% nr! o# colu"ns(!

Close the "ap window and dou$le1clic2 the Su$irst Colu"n !

Type /J7 in the te.t $o. u"$er o# Lines and /-7 in the te.t $o. u"$ero# Colu"ns !

Type #or ?utput Raster

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Spatial data managementhas to $e e.tracted can $e #ound!

&ou can use the sa"e "ethod to e.tract the sa"e area #ro" the "ap 9oliviaB"as2%and then create a #inal "ap only showing the hillshading #or the country o# 9olivia!

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Glueing raster maps

The 8lue Raster

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Spatial data managementIn this e.ercise two parts o# a T< i"age% one covering the northern 'T"$)Bnorth(and the other covering the southern part 'T"$)Bsouth( o# the study area% are gluedtogether! 9oth "aps have the i"age do"ain!

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I# you select the Last

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"esampling

In "any cases% the raster operations shown a$ove will not $e su##icient to get youri"ported raster data in the correct #or"% to co"$ine the" with other "aps! The pi.elsi e "ay $e di##erent #ro" the other "aps% or the "ap "ay lac2 coordinates! Tooverco"e these pro$le"s% the "ap should $e resa"pled to another e.isting raster"ap in your data $ase! Resa"pling will $e e.plained in "ore detail in chapter /%dealing with i"age processing! Here it is i"portant to note that "any o# the tools%originally designed #or i"age processing% are e:ually valua$le when wor2ing withother types o# raster "aps!

Suppose that you have received a geological "ap #ro" so"eone else! Suppose thatapart #ro" the digital #ile you also received a ta$le with a series o# control points! I#these were "issing you would have to #ind out control points yoursel# $y co"paringthe raster "ap with a topographic "ap% or with another digital "ap! This is shown in

chapter /! Here it is assu"ed that )7 control points are 2nown! The ne.t thing to do isto "a2e a geore#erence #or this "ap% using the control points listed in Ta$le 4!/!

GI# a digital ta$le with tiepoint data is availa$le% you can also use Copy and Paste

?pen raster "ap 8eology! >ro" the >ile "enu o# the "ap window select Create% 8eoRe#erence ! The

Create 8eoRe#erence dialog $o. is opened!

Type #or the 8eoRe#erence a"e 5 8eology! Accept the de#ault option 8eoRe# Tiepoints ! Select the Coordinate Syste" 5 Cocha$a"$a and clic2 ?@ ! The

8eoRe#erence Tiepoints editor is opened! >ro" the Edit "enu in the 8eoRe#erence Tiepoints editor select Add Tie Point or pressthe Add Tie Point $utton inthe Tool$ar o# the editor!The Add Tiepoint dialog $o. is opened!

Type the Row% Colu"n% O and & coordinates #or the #irst point as shown inTa$le 4!/!

Repeat this #or the other tiepoints! The trans#or"ation should displayA##ine% and theSig"a 'the error( should $e lower than )!

Close the 8eoRe#erence Tiepoints editor $y clic2ing the E.it Editor $ut1ton ! Raster"ap 8eology is now geore#erenced!

Close the "ap window!

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Spatial data managementto insert your data in the 8eore#erence Tiepoints editor!


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+a,le 4.*& Tiepoint locations #or the raster "ap 8eology!

7 "o /olumnJ J -- 7 /)- )*J )/-

74) - 7 J7 - ** - )74 )- 7 7) - / /*J J4)- 7 7,,- /J )*777J 7 , ,7 44/ ,7/7*,4, 7 ) - -/ 4-J77 ,- 7J,4-7 )), ,-JJ /4-- 7J* /- ))JJ /-J /7-7 7 ,/* 4/7 ,7* J, 7 7 7 / 4

ow that the raster "ap 8eology is geore#erenced% you can resa"ple it to anotherraster "ap% #or e.a"ple Landuse% which uses the geore#erence Cocha$a"$a!

0ou$le1clic2 Resa"ple in the ?peration1list ! The Resa"ple Raster

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GI# you want to practice so"e "ore with resa"pling% you can generate control points #ro" the polygon "ap City$loc2 'city $loc2s o# Cocha$a"$a(% and usethese to geore#erence the raster "ap Airphoto 'scanned aerial photograph o# the

center o# Cocha$a"$a(! Then rasteri e the polygon "ap City$loc2 'with a pi.elsi e o# - "eters( and resa"ple the "ap Airphoto!

9diting raster maps

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Editors can only $e used to edit source maps ! 'ependent maps 'e!g! the raster "apcreated $y rasteri ing a polygon "ap( and "aps which are de#ined in their properties#or" as read only % cannot $e edited! Conceptually% it would not $e a good idea to edit

a dependent "ap% since such a "ap is derived #ro" source "aps% which are notchanged in that case! To edit a dependent "ap% you should either edit the source"ap's( and use the ro" the Edit "enu in the "ap window% select Edit Layer % and ) "apWrong! The Pi.el editor is opened!

Uoo" in on the word E0IT and clic2 the or"al $utton!

Select with the le#t "ouse $utton a part o# the letter E which is surrounded $y green pi.els $y dragging a $o.!

Press the right "ouse $utton and select Edit #ro" the Conte.t1sensitive"enu! The Edit dialog $o. is opened!

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In the Pi.el editor% you can select one or "ore pi.els $y clic2ing the" or dragging a

$o. around the"% in order to change their class na"e% I0% or value! &ou can add pi.els to a selection% clear a part o# a selection or toggle $etween select and deselect pi.els!

1 To add pi.els to a selection5Press and hold the CTRL 2ey and clic2 the other pi.els you want to select!

1 To clear a part o# a selection5Press and hold the CTRLXSHI>T 2eys% then clic2 previously selected pi.els ordrag a $o. around the"!


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1 To toggle $etween selecting and deselecting pi.els5Press and hold the SHI>T 2ey% then clic2 pi.els or drag a $o. around pi.els'selected pi.els are deselected and non1selected pi.els are selected(!

"aster to e$tor $on#ersion

So"eti"es it can $e necessary to convert raster "aps $ac2 to vector "aps! This can $e the case i# you o$tain a the"atic raster "ap $y i"porting a digital #ile #ro" othersources! I# you want to edit the "ap e.tensively% it is $etter not to do that with thePi.el editor! It is $est to convert the raster "ap to polygons #irst% then e.tract seg"entsand create la$els% and do the editing in the Seg"ent editor% a#ter which you polygoni eand rasteri e the "ap again! It "ay also $e use#ul to convert raster "aps $ac2 tovector "aps i# you want to use the" #or high :uality "ap production!

To convert raster data to vector data #or"at% a ,., "atri. "oves over the input "apand assigns a code 'class na"e% I0 or value( to the center pi.el o# the "atri. in theoutput "ap% which depends on the class na"e% I0 or value o# the center pi.el and its4 or neigh$ours! See chapter #or "ore in#or"ation a$out 4 or 1connectivity!

Practice with these various options! Edit the "ap so that the word E0IT isreplaced $y the pi.el values o# the areas surrounding it!

E.it the Pi.el editor $y pressing the E.it Editor $utton!

Close the "a window when ou have #inished the e.ercise!

0ou$le1clic2 the Raster to Polygon operation in the ?peration1list ! ThePolygons o# Raster

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Spatial data management3nde#ined pi.els will not $e vectori ed! The result o# the conversion depends on theho"ogeneity o# the raster "ap and the pi.el si e co"pared to the si e o# the "appingunits! The progra" is provided with a s"oothing #acility% to re"ove the sharp corners#or"ed $y the $oundaries $etween "apping units o# the raster "ap! Auto"atictunneling 'see chapter ,( is per#or"ed on the coordinates o# the vector data to deletethe redundant ones! In this e.ercise the raster "ap Slopeclass is converted to a

polygon "ap!


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ow you will see the e##ect o#

converting a raster "ap toseg"ents! When you con1vert #ro"

raster to seg"ents% only the $oundary lines $etween "apping units are stored% $ut insuch a way that it is still possi$le to #ind out what the "apping units on $oth sides o#

the line are!

The output "ap resulting #ro" the raster to seg"ent conversion uses a uni:ue I0do"ain and an attri$ute ta$le with , colu"ns5 Area)% Area* and Length! Area) andArea* have the do"ain o# the input raster "ap and indicate the right and le#t area! Thecolu"n Length gives the length o# the seg"ent! >or e.a"ple% 9oundary) is theseg"ent $etween an area with class a and an area with class $ '>igure 4!-(!

In the Catalog % clic2 with the right "ouse $utton on raster "apSlopeclass and select Dectori e %Raster to Seg"en t!The Seg"ents o# Raster

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Spatial data management)igure 4.%& Conversion o# a raster "ap to a seg"ent "ap 'see the te.t #or e.planation(!


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Summar!& "aster data management

The #ollowing tools can $e used #or raster data "anage"ent5

1 Copying a rectangular part o# a raster "ap into a new raster "ap% using theSu$

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4.* 5omain $on#ersion

In the previous e.ercise% especially during the e.ercise dealing with i"port% you haveseen that in ILWIS your "ap "ay have another do"ain than you would li2e!So"eti"es the do"ain o# a "ap should $e changed% e!g!% converting a do"ain valueto a do"ain class! In this e.ercise the various "ethods #or do"ain conversion aretreated!

arning a,out $hanging domains

Apparently the easiest solution #or changing the do"ain type would $e to si"plychange the do"ain in the Properties sheet o# the "ap! This should $e done with careGThis "ethod is only reco""ended #or converting $etween do"ains o# the sa"e type'e!g! #or converting a class do"ain Landuse to a class do"ain Landuse)(! &ou should"a2e sure% however% that the two do"ains have the sa"e ordering o# the raw values! I#the ordering is di##erent% than the na"es in the "ap will $e "i.ed a#ter changing thedo"ain!

Changing do"ains o# "aps via the Properties sheet% is not reco""ended #or changing#ro" one do"ain type to another 'e!g! #ro" do"ain class to do"ain value(! I# you dothat your #ile "ay $eco"e corrupt! >or changing do"ain types% #ollow the guidelinesdescri$ed $elow!

/on#ersion ,et een an I5 domain and a $lass domain

Class do"ains and identi#ier do"ains are not so di##erent! It is% there#ore% easy toconvert #ro" one type to the other! The conversion #ro" a class do"ain to an


In the Catalog % clic2 the do"ain Landuse with the right "ouse $utton andselect Properties ! The Properties sheet is opened! As you can see thedo"ain contains )* do"ain ite"s!

Press the Convert to identi#iers $utton! The class do"ain is converted to anidenti#ier do"ain!

?pen the Properties sheet o# the do"ain Landuse again! ow you can seethat it reads5 0o"ain Identi#ier LanduseN !

Press the Convert to classes $utton! The I0 do"ain is converted $ac2 to a

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Spatial data managementidenti#ier do"ain can $e done $y clic2ing the $utton Convert to classes in the Properties sheet o# an I0 do"ain! The conversion #ro" a class do"ain to an identi#ier do"aincan $e done $y clic2ing the $utton Convert to identi#iers in the Properties sheet o# theclass do"ain!

Ta2e #or e.a"ple the polygon "ap Landuse% containing the land use types in thestudy area! This is a class "ap!

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The conversion #ro" classes to identi#iers is not very logical #or the "ap Landuse%since each land use class contains various polygons! An identi#ier do"ain is generallyuse#ul i# each do"ain ite" is lin2ed to one "ap #eature 'point% seg"ent% polygon% or

group o# connected pi.els in a raster "ap(!

There is% however% a way to convert a class "ap to a uni:ue I0 "ap% using the 3ni:ueI0 operation! This operation can $e used to give a uni:ue I0 to all #eatures in aseg"ent% polygon or point "ap! The results o# the operation are a "ap and an attri$uteta$le with the sa"e na"e! The output "ap uses the syste" do"ain 3ni:ue I0! Theoutput ta$le has the sa"e do"ain as the output "ap and consists o# two colu"ns%containing the original class na"es and the areas o# each polygon! The in#or"ation inthe colu"n consists o# the classes% I0s or values o# the original "ap per I0 in theoutput "ap!


0ou$le1clic2 3ni:ue I0 in the ?peration1list ! The 3ni:ue I0 dialog $o. isopened!

Select polygon "ap Landuse in the list $o. Input

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The 3ni:ue I0 operation can only $e per#or"ed on vector "aps! The e:uivalentoperation #or raster "aps is called Area u"$ering % which will $e treated in Chapter!

/on#erting a $lass or an I5 domain to a #alue domain

The conversion #ro" a class or an identi#ier do"ain to a value do"ain% can $est $edone $y creating an attri$ute "ap #ro" a value colu"n o# the "ap s attri$ute ta$le!

Ta2e #or e.a"ple the "ap City$loc2% which is a "ap using an identi#ier do"ain% inwhich each $uilding $loc2 o# the city o# Cocha$a"$a has a separate code! Lin2ed tothat "ap is an attri$ute ta$le City$loc2 which contains% a"ongst others% in#or"ationon the nu"$er o# persons living in each city$loc2 'colu"n Population(!

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In this case the conversion #ro" identi#ier to value only "a2es sense when you wantto create #or e.a"ple a population "ap!

The si"ple conversion o# the "ap City$loc2 #ro" identi#ier to value do"ain would"a2e no sense! I# you do that the values have no logical "eaning% and $esides that%the "ap can no longer $e lin2ed to an attri$ute ta$le!

/on#erting a #alue domain to a $lass or an I5 domain


Close polygon "ap City$loc2!

In the Catalog clic2 polygon "ap City$loc2 with the right "ouse $uttonand select Dector ?perations% Attri$ute

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Spatial data managementThe conversion #ro" a value or an i"age do"ain to a class do"ain "ay so"eti"es $enecessary! >or e.a"ple% when you have i"ported a scanned the"atic "ap as a grayscale TI> #ile! When you want to convert #ro" a value "ap to a class "ap% you should2now the na"es o# the legend units that should $e assigned to the di##erent values!

>or the conversion #ro" a value "ap to a class or I0 "ap% there are two possi$ilities51 When you have a value "ap that has values with a precision other than )% you

should create a group do"ain 'in which the $oundary values and the class na"esare indicated( and use the Slicing operation as descri$ed in chapter J! An e.a"ple o#this is the classi#ication o# a 0igital Elevation

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+a,le 4.:& Relation I0 and Class na"es!

I5 /lass namenr ) Agriculturenr * Agriculture 'irrigated(nr , Airport


?pen the raster "ap Landi"age and clic2 so"e pi.els in the "ap! As youcan see the "ap displays nu"$ers instead o# class na"es!

Close the "ap window and select Create% 0o"ain #ro" the >ile "enu inthe

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Spatial data managementnr 4 9are roc2nr - 9are soilsnr / >orestnr J 8rasslandnr La2enr River$ednr )7 Shru$s

nr )) 3r$an centrenr )* 3r$an periphery

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/on#erting a pi$ture domain to a $lass domain

The conversion #ro" a picture do"ain to a class do"ain% can $e done $y clic2ing the $utton Convert to Classes in the Properties sheet o# the do"ain! I# you want to convert a picture do"ain to an identi#ier do"ain% you #irst convert the picture do"ain to classesand then press the $utton Convert to Identi#iers in the Properties sheet o# the class do"ain!

This type o# conversion is also :uite co""on% a#ter i"porting a Windows $it"ap!9

#ile! Si"ilarly #or the conversion #ro" value to class% you should 2nowwhich pi.el values represent which classes!

This is illustrated with "ap Landpicture that was i"ported with a picture do"ain!It should $e a class "ap% with in#or"ation on land use types!


0ou$le1clic2 raster "ap Landpicture! In the 0isplay ?ptions Raster

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/on#erting a pi$ture domain to an image domain

The conversion #ro" a "ap with a picture do"ain to an i"age 'or value( do"ain "ayso"eti"es $e necessary! >or e.a"ple% the i"port o# TI> color #iles or 9

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is the na"e o# the output "ap! In the Raster

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+a,le 4.8& 0o"ain conversions in ILWIS!

)rom +o "e$ommended pro$edure

Class I0 Properties% $utton Convert to identi#iers

Class or I0 Dalue Attri$ute ta$le;colu"n Attri$ute

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Summar!& 5omain $on#ersion

&ou should $e care#ul when changing the do"ain o# a "ap! I# you do not #ollow theguidelines descri$ed in this section% the #ile "ay get corrupt!

The #ollowing do"ain conversions are possi$le in ILWIS5

1 Conversions $etween class and I0 "aps% is easily done $y pressing the Convert toIdenti#iers $utton or the Convert to Classes $utton% in the Properties sheet o# the do"ain!

1 Conversion #ro" class or I0 to value% is done $y creating an attri$ute "ap with a

value colu"n #ro" an attri$ute ta$le!

1 Conversion #ro" a value do"ain to a class;I0 do"ain% can $e done either $y usingthe Slicing operation 'when the value "ap has a precision other than )(% or $ycreating an I0 do"ain% and replacing this in the Properties sheet o# the "ap 'whenthe value "ap has a precision o# )(!

1 Conversion #ro" a picture do"ain to a class do"ain can $e done% $y pressing theConvert to Classes $utton in the Properties sheet o# the do"ain! Conversion to I0 do"aincan then also $e done 'see a$ove(!

1 Conversion #ro" a picture do"ain to an i"age or value do"ain can $e done% $yusing a

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