GIS Analisi Dalam GIS - Week 10 Baru

8/10/2019 GIS Analisi Dalam GIS - Week 10 Baru

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Analisis-analisis dalam GIS


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Historically, overlay was one of the first ways

in which people combined map information toproduce a new map.


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all layers must be

drawn to the same

scale in the same

projection to ensure

they overlay properly

often required re-

drafting of maps:

time consuming

and error proneautomated overlay

became one of the first

objectives for GIS


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Operasi tindanan

most applications of geographic informationmust integrate information from differentsources - overlay plays a key role

procedure: 1. Georeferencing

2. Geometric Intersection Processing raster implementations

vector implementations

3. Attribute Combination


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1. Georeferencing

o knowledge of the absolute location of each

feature is a universal requirement


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2. Geometric Intersection Processing

2 basic types of overlay operations: (a)

arithmeticand (b) logical: (a) Arithmetic Overlay

arithmetic operations (addition, subtraction,

multiplication, division, etc.) between data values

in corresponding locations in multiple data layers


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Vector Overlay each polygon can differ in size and shape so their

boundaries will not usually coincide between data layers attributes are stored in separate attribute tables

if polygons A and D do not overlap or if one is totallycontained within the other, then little additional effort isneeded

if polygons A and D do overlap, the area of overlap must be

defined as a separate new polygon and assigned a newattribute value

clipping- the process of subdividing polygons duringoverlay


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1. find all intersections between the boundary

lines of the polygons 2. these intersections become new nodes in

the result image

3. topology must be built and all new/existing

polygon tables must be updated with a newpolygon definition


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4. a new attribute table is created

efficient overlay processing requires carefuluse of topology (e.g. left & right polygon id's)

to limit calculations

although there will be fewer arithmetic

operations than in the raster case, clippingmakes vector overlay operations

considerably more complex


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slivers- small polygons created during overlay from

slight differences in the representation of boundaries

that should have been the same.

mis-registration of sources

temporal differences

inaccuracy of one database relative to another

fuzzy tolerance- a distance within which intersections andpoints are treated as being coincident.


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(b) Logical (Boolean) Overlay

overlay binary images

Logical AND overlay with multiply

Output = 1 only where

Image1 AND Image2 =1


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Logical OR

overlay withadd; reclass 2

to 1

Output = 1

where Image1

OR Image2 = 1


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Logical XOR

overlay withadd; reclass

2 to 0

Output = 1

where

Image1 OR

Image2 = 1,

but not both


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Logical NOT

overlay to select undesired class; reclassto reverse coding: reclass 0 to 1, reclass 1

to 0

Output =1 where Image1 =0


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3. Attribute Combination

once all the spatial information is into a commongrid, raster overlay analysis requires only some

relatively simple attribute manipulations vector overlay analysis may be more complicated,

especially if more than one polygon on Image1overlays on a single polygon on Image2: whoseattribute should Image2 receive?

many modern GISs use a hybrid approach to takeadvantage of the capabilities of both data models


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Aplikasi tindanan

Many Layer Update

Multivariate Classification Cut & Fill

Accuracy Assessment

Change Detection

identify areas of change between coincident datasets acquired several years apart

coverages must use identical categories

Documents

GIS Analisi Dalam GIS - Week 10 Baru