lab1 introduction to vector and raster

8/16/2019 LAB1 Introduction to Vector and Raster

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SGHU 4133TOPOGRAPHIC MAPPING USING

REMOTELY SENSED DATA

LAB. 1INTRODUCTION TO RASTER GRIDS


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the grid lines intersets8 this point is re(erred to as a 9node9.

Deter!ine the (ollo'ing:

o' !an& total ro's o( grid lines do &o$ observe

on the !ap,

o' !an& total ol$!ns o( grid lines do &o$

observe on the !ap,

Divide the total 0 $nit distane "(ro! 1*-% b& then$!ber o( ol$!ns

Divide the total $nit distane "(ro! 1*-% b& the

n$!ber o( ro's

+hat is the 0 $nit distane overed bet'een eah

node,

+hat is the $nit distane overed bet'een eah

node,

Are the nodes distrib$ted on a per(etl& s)$are or

retang$lar grid net'or;,

1*< onsider a h&pothetial exa!ple "not related to the attahed

5g$re% Ass$!e the (ollo'ing !ap oordinate relationships:


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Ta& A2'. ?aster data in geographi in(or!ation s&ste!s is basiall& a

grid net'or; o( data8 'ith 08 node oordinates and a 9@9 val$e "i.e. so!eattrib$te% attahed to eah node point. n the ase o( 9digital elevation

!odels9 "also ;no'n as DEMBs%8 the 9@9 attrib$te val$e is elevation relative

to sea level. o$r tas; here is to reate a digital elevation !odel "gridded

elevation data% (or the area seleted on the #ig$re 18 as o$tlined 'ith the

dar; retangle in the enter. The seleted nodes are highlighted 'ith a

heav& 9dot9.

Ass$!e that the 5rst ro' and 5rst ol$!n o( the grid starts in the lo'er

le(t hand orner "i.e. the so$theast orner o( the !ar;ed grid%. This point is

!ar;ed as 9grid origin9 on the !ap. This is analogo$s to a artesian

oordinate s&ste! $sed in !athe!atial graphing. #ill in the (ollo'ing

harts:

Eastingoordinates

Northingoordinates

ol$!n 1 ?o' 1

ol$!n - ?o' -

ol$!n / ?o' /


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)

C!$-%#5 Statemet t! Part A. Ra&ter Gr#%&

o$ no' have an $nderstanding o( ho' raster grid data is reated and

stored in eographi n(or!ation S&ste!s. The st$d& area is divided into a

!esh o( grid ells8 'ith eah node attahed to so!e attrib$te in(or!ation

"i.e. 9@9 val$es%. Eah ell is given a n$!eri identi5er or val$e. ?aster

s&ste!s are good (or representing data over ontin$o$s spae8 exa!plesinl$de:

o Digital pit$res or i!ages "eah ell is assigned a olor val$e8 here a

ell is alled a 9pixel9%

o Digital Elevation Models "eah ell is assigned an elevation%

o ?ain(all Maps "eah ell is assigned a rain(all val$e * inhes o(preipitation a$!$lated over ti!e%

o egetation !aps "eah ell is assigned a vegetative index n$!ber%

Last Question: Thin; $p three exa!ples o( spatial !ap data8 other than

the exa!ples listed above that o$ld e!plo& digital raster tehni)$es.


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o Pol&gons * reg$lar to irreg$larl& shaped pol&line sets that

o!pletel& lose on the!selves "i.e. the end point o( the pol&line

exatl& !athes the origination point o( the pol&line%.

GG A Side Note: n the ase o( the vetor approah to !ap ele!ents8 t'o

so(t'are 5les are re)$ired: "1% a vetor graphis 5le 'ith the geo!etri

oordinates and !ap ele!ent t&pes. ere the !ap ele!ent is assigned an

internal ode8 and "-% a database in(or!ation 5le that lin;s attrib$tes to

the internal ode o( the !ap ele!ents.

This is diFerent than the raster grid data str$t$re above8 in 'hih all data

an easil& be stored in one data 5le. ene8 vetor !ap la&ers $s$all&

re)$ire !$ltiple data 5les to !anage the sa!e in(or!ation that one raster

data 5le represents.GG

E7am#e 6#5-re 'A (or a o!parison o( pol&gon !ap ele!ents

represented in a vetor vs. raster data str$t$re.

Ta& B21. ?e(er to #ig$re /. This is a !ap grid in UTM*!eters8 'ithseveral digital !ap (eat$res listed A thro$gh E. denti(& 'hih t&pe o( !ap

ele!ent is represented b eah (eat$re in the table belo "point line


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Ta& B2'. 2$ild a vetor data 5le (or eah !ap (eat$re "A thro$ghE% in the table belo'.

8-e&t#!&:

+hih data t&pe do

&o$ thin; re)$ires

!ore o!p$ter

storage !e!or& andproessing ti!e8

vetor or raster,

+h&,

#eat$re Node oordinates

0 oordinate oordinate

A

2

node 1

node -

D

node 1

node -

node /

node 3


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Using a red olored box "or an& other olor o( &o$r hoosing%8 onvert

vetor !ap ele!ents A thro$gh E to 9?aster !ap ele!ents9. Using thegrid net'or; sho'n on #ig$re /8 olor in the raster version o( eah o( the

ele!ents "hint: re(er to #ig$re -A (or so!e ideas%.


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lab1 introduction to vector and raster

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