Grid Functions

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Grid Functions

• FE 423 - Lecture 3b

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SCHEDULE
3
OUTLINE

• Grid Function List
• Writing Equations
• Conditional
• Setnull/Isnull
• Local/Focal/Zonal Functions
• Project/Disc Management

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Grid Function List

• ArcView Help Grid (Class)
• We only use those ending in Grid
• and not those with
• Ftab
• aPrj
• aGridList

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WRITING EQUATIONS

• In math yx2
• Old computer code ysqr(x)
• Object oriented code x.sqr
• Nesting log(sin(x)) ? x.sin.log
• parameters dem.hillshade(315,45,1)

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Conditional Statement0/1 to grid0/grid1

• If condition
• then action1
• else action0
• in Avenue
• aGrid.Con (yesGrid, noGrid)
• Example
• (snowgtmelt).Con((snow-melt),0.Asgrid)

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Null Data

• Cells with no value (not 0) are null
• Some functions require null cells
• Some functions make null cells
• Setnull sets specific cells to null
• (stand agegt100.Asgrid).SetNull(stand age)
• Isnull is a cell value null?
• (landslides.Isnull).Con(0.Asgrid,1.Asgrid)

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Local/Focal/Zonal Functions

• Local Functions
• at each cell
• grid1grid2
• Focal Functions
• around each cell
• dem.FocalStats(GRID_STATYPE_MEAN,
  NbrHood.Make, False)
• Zonal Functions
• within the zone of each cell
• (demgt1000.asgrid).ZonalFill(dem)

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PROJECT MANAGEMENTevery project tells a story

• Make project name explanatory
• Make themes name explanatory
• Make legend categories clear
• Comment themes to explain thinking
• Remove useless themes
• Separate unrelated themes by project

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DISC MANAGEMENTmake and move everything together

• Use one directory on all machines
• C/temp/email_name/this_project/
• Set Working Directory
• Save coverages, files, project, report
• zip directory to move
• by network
• by zip drive
• email/ftp

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Reading from ArcDoc

• Spatial modeling
• Cell-based Modeling with GRID
• Surface hydrologic analysis