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ESRM 250/CFR 520 Autumn 2009 Phil Hurvitz

Raster Analysis 1. ESRM 250/CFR 520 Autumn 2009 Phil Hurvitz. Overview. Raster layers Setting raster layer and analysis properties Raster function types Performing raster analysis Map Algebra. Overview. Raster layers Setting raster layer and analysis properties Raster function types

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ESRM 250/CFR 520 Autumn 2009 Phil Hurvitz

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  1. Raster Analysis 1 ESRM 250/CFR 520Autumn 2009 Phil Hurvitz 1 of 52

  2. Overview • Raster layers • Setting raster layer and analysis properties • Raster function types • Performing raster analysis • Map Algebra 2 of 52

  3. Overview • Raster layers • Setting raster layer and analysis properties • Raster function types • Performing raster analysis • Map Algebra 2 of 52

  4. Raster layers: Overview • Raster layer types • Raster layer properties • Adding raster layers to views • Displaying raster layers • Examining cell values in raster layers • Managing raster layer files 3 of 52

  5. Raster layers: Overview • “Grid” layers are ArcView's implementation of the basic raster data model. environmental data are represented as “grid” raster layers (image from ESRI) 4 of 52

  6. Raster layers: Overview • Grid layers are ArcView's implementation of the basic raster data model. rectangular tessellation of square cells 5 of 52

  7. Raster layers: Overview • Grid layers are theoretically different from image layers • Grids and images are stored in the same basic (raster) format: a rectangular matrix of cells where each cell has a value • Image layers always represent remotely sensed imagery (e.g., digital orthophoto) • Grids typically represent other continuous phenomena (e.g., slope, salinity) 6 of 52

  8. Raster layers: Overview • All images are rasters. • All grids are rasters. • NOT all rasters are images or grids rasters grids images 7 of 52

  9. reflectance values Raster layers: Overview • Grid layers are different from image layers • These are image layers 8 of 52

  10. elevation etc. values Raster layers: Overview • Grid layers are different from image layers • These are grid layers 9 of 52

  11. Raster layers: Overview • Grid layers are different from image layers 10 of 52

  12. Raster layers: Overview • Grid layers are different from image layers cellshave numerical value that representa numericalvariable 11 of 52

  13. Raster layers: Overview • Raster layers are suited for representation of phenomena that vary gradually over space e.g. elevation, wind speed, or slope 12 of 52

  14. integer (no decimals) floating-point(decimals) Raster layers: Raster types • Only integer rasters can have layer tables 13 of 52

  15. Raster layers: Raster types • Only integer rasters can have layer tables will not have a table will have a table 14 of 52

  16. Raster layers: The spatial analyst • All raster layer functionality occurs through the Spatial Analyst extension. • Loading of raster layers for analysis • Raster analysis • Spatial analyst must be enabledto perform raster analysis 15 of 52

  17. Raster layers: Raster layer properties • Layer description contains a lot of information 16 of 52

  18. Raster layers: Raster layer properties • Layer description contains a lot of information 17 of 52

  19. Raster layers: Raster layer properties • Layer description contains a lot of information 18 of 52

  20. Raster layers: Adding raster layers to views • Add raster layers in the same way as adding other data sets 19 of 52

  21. Raster layers: Displaying raster layers • Usually numerically classified • Symbology can be altered like other layers 20 of 52

  22. Y-axis: cellcounts in eachvalue class X-axis: values Raster layers: Examining cell values with histogram • Histograms describe structure of data values 21 of 52

  23. Raster layers: Examining cell values with identify tool • Individual cell values can be identified as with feature data 22 of 52

  24. Raster layers: Examining cell values with queries • Integer rasters can be queried in the usual way • Selected sets/cells shown in cyan 23 of 52

  25. Raster layers: Managing raster layer data files • Raster data sources should always be managed by ArcCatalog • copying • moving • renaming • deleting 24 of 52

  26. Overview • Raster layers • Setting raster layer and analysis properties • Raster function types • Performing raster analysis • Map Algebra 26 of 52

  27. Setting raster analysis properties • Analysis properties determine spatial properties for all newly created output raster layers • Analysis properties: • Working directory • Analysis mask • Analysis extent • Cell size • Once set, analysis property values stay set until changed • [Settings described below] 27 of 52

  28. Setting raster analysis properties: working directory • Working directory specifies the default location for new rasters created with the Spatial Analyst Extension 52

  29. Setting raster analysis properties: Analysis extent • Analysis extent sets the spatial properties for output of analyses • Extent is a rectangular area 28 of 52

  30. Setting raster analysis properties: Analysis extent • Be careful about setting extent; it may cause poor raster-to-raster registration 29 of 52

  31. Setting raster analysis properties: Analysis extent • Be careful about setting extent; it may cause poor raster-to-raster registration • Use “snap extent to” 29 of 52

  32. Setting raster analysis properties: Cell size • Analysis cell size sets the raster cell size for output of analyses • Use consistent cell size for analysis of multipleraster data sets • Note: • small cells → larger files (-) • small cells → longer processing (-), but … • small cells → usually greater accuracy (+) 30 of 52

  33. Setting raster analysis properties: Masking • Analysis mask defines “valid data extent” of output rasters • A mask can have any shape (whereas analysis extent is always rectangular) 31 of 52

  34. Setting raster analysis properties: Masking • Analysis mask defines “valid data extent” of output rasters “mask_grid” has a specificextent of valid data (in green) output matches the same data extent 32 of 52

  35. Overview • Raster layers • Setting raster layer and analysis properties • Raster function types • Performing raster analysis • Map Algebra 34 of 52

  36. Raster function types • Local functions • Global functions • Zonal functions • Focal functions 35 of 52

  37. local sine e.g. sin(12) = -0.537 Raster function types: Global functions • Local functions apply an independent calculation to all input raster cells • Each output cell’s value is calculated independently 36 of 52

  38. Raster function types: Global functions • Global functions apply a calculation considering all cell values the value 3 is calculated by knowing that flow comes from other cells the value 5 is calculated byknowing that flow comes from other cells, cumulatively e.g. flow accumulation 37 of 52

  39. Raster function types: Zonal functions • Zonal functions apply one calculation to all input raster cells within each zone zones are defined as a group of cells having the same value 38 of 52

  40. Raster function types: Zonal functions • Zonal functions apply one calculation to all input raster cells within each zone zonal sum for zone 1: (53 + 57 + 33 + 78 + 31 + 12 + 32 + 9 + 9 + 33 + 76) = 423 all cells in zone 1 in the output are given value 423 39 of 52

  41. focal mean Raster function types: Focal functions • Focal functions apply one calculation to all input raster cells within a “focus” (27 + 8 + 22 + 16 + 21 + 16 + 6 + 44 + 8) / 9  18.7 The “focal” cell in the output grid is given value 18.7 40 of 52

  42. Overview • Raster layers • Setting raster layer and analysis properties • Raster function types • Performing raster analysis • Map Algebra 41 of 52

  43. Raster analysis: calculations across multiple rasters • Multi-raster analyses are possible because of spatial registration • multiple raster layers share the same X, Y coordinate space • cell values are calculated across multiple raster layers • to create a single output raster layer 42 of 52

  44. Raster analysis • Analyses are performed using GUI tools • Spatial Analyst toolbar > Raster Calculator 43 of 52

  45. Raster analysis • Analyses are performed using GUI tools • ArcToolbox tools 44 of 52

  46. Raster analysis • Many more raster analyses are available through the Raster Map Algebra syntax, which can be used in the Raster Calculator or custom tools 45 of 52

  47. Overview • Raster layers • Setting raster layer and analysis properties • Projections and raster layers • Raster function types • Performing raster analysis • Map Algebra 46 of 52

  48. Raster analysis: Map algebra (or “How it works”) • Raster layers may be used in arithmetic expressions in the raster calculator output_data_set = input_raster1 operator input_raster2 ... e.g., slp_dem = slp_raster * dem output input 1 input 2 operator 47 of 52

  49. Raster analysis: Map algebra (or “How it works”) • Raster layers may be used in algebraic functions in the raster calculator output_data_set = function (input_data_set[s]{,arguments}) e.g., slp_raster = slope (dem, percentrise) output input 1 function input 2 47 of 52

  50. operator classes operators raster layers expressionbox Performing raster analysis: Using rasters in math • Map algebra is calculated with the Raster Calculator 48 of 52

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