LAB1 Introduction to Vector and Raster
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Transcript of 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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Lab. 1 P a g e |
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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Lab. 1 P a g e |
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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Lab. 1 P a g e |
)
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)$es.
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Lab. 1 P a g e |
o Pol&gons * reg$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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Lab. 1 P a g e |
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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