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Continuous vs. Categorized
• Continuous:– Like photographs– Satellite and aerial photos– Best for analysis
• Categorized or discrete– Land Cover– Eco-regions– Limited analysis– Careful on precision and accuracy
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“No-Data” or NULL Values
• Rasters are always rectangular
• No-Data values are “transparent” and are not used for calculations
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Geo-Referenced Raster
• Known Projection and Datum
• Width and height of a pixel in map units
(X1,Y1)
Width in Pixels
Height in pixels
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Geo-Referenced Raster
• Known Projection and Datum
(X1,Y1)
(X3,Y3)
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Types of Rasters
• Digital Elevation Model (DEM)
• Digital Raster Graphic (Topos)
• Satellite and Aerial Photos
• Land Cover & other natural characteristics
• Cost Distance & other economic
• Population, taxes, etc.
• Your own!
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Aspect – Direction of the slope
Slope
Aspect (Direction)
Angle
Rise
Run
Slope = (Rise/Run) * 100%
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Creating a Hillshade
• Obtain a DEM
• Crop to Desired Area
• Create Hillshade
• Apply color ? To DEM
• Add DEM over Hillshade with Transparency
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• Screen shots:– Hillshade dialog– Colorizing dems– Transparency
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Spatial Analyst Extension
• Make sure “Spatial Analyst” is Checked
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Tool Bar
• Right-click in the menu area
• Select “Spatial Analyst”
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Hill-shading
• Azimuth: “Direction” of the sun relative to the ground. 0 is north.
• Altitude: Angle from the horizon to the sun.
North
Azimuth
Altitude
Horizon
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Continuous vs. Categorized
• Continuous:– Like photographs– Satellite and aerial photos– Best for analysis
• Categorized or discrete– Land Cover– Eco-regions– Limited analysis– Careful on precision and accuracy
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“GeoReferenced” File Formats
• GRID: ESRI’s format
• GeoTIFF: Excellent support
• MrSID: LizardTech
• IMG: ERDAS
• ECW: ERMapper
• BIL, BIP, BSQ: See header (w/prj)
• “ASCII” or “GRID ASCII” (w/prj)
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World Files
• Contains:– X-dimention Pixel size in map units– Y-axis rotation– X-axis rotation– Y- dimension Pixel size in map units
(negative)– X-coordinate of upper-left pixel– Y-coordinate of upper-left pixel
• Image file contains width and height
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Not Geo-Referenced
• BMP
• PNG
• GIF
• JPEG
• Maybe with a world file and prj file?
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JPEG
• Joint Photographic Experts Group
• Widest used photo format
• Not for use with vectors
• JPEG2000– Completely new format!– Can be georeferenced
Edge of Rocky Mountain National Park Boundary with high JPEG compression
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Tagged Image File Format
• TIFF• Can be georeferenced (GeoTIFF)
– Can tell in ArcCatalog or ArcMap
• TIFF w/world file– Also need Projection and Datum (prj?)
• Can be compressed– Run-length – Categorical data– LZW – Categorical data– Huffman encoding – Categorical data– JPEG- Continuous data (don’t used on
Categorical data!)
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GRIDS
• ESRI’s native raster format
• Pyramids
• Not an exchange format!
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ASCII format• NCOLS 10• NROWS 9• XLLCORNER 1000• YLLCORNER 1000• CELLSIZE 1• NODATA_VALUE -9• -9 -9 1 1 0 1 0 1 -9 -9• -9 -9 1 1 2 2 2 1 1 -9• -9 1 1 1 2 2 2 2 3 3 • Etc.• See example
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Types of Rasters
• Land Cover: forest, grass, water, roads, urban
• Digital Elevation Model: DEM
• Aerial Photos
• Satellite Photos
• Scanned: DRG, 24k Topos
• Derived rasters: lots!
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Derived Rasters
• Land Cover from satellite and aerial
• Topography: Slope, aspect, hillshade
• Ecoregions• Suitable Habitat• Flood plains• Geological Regions
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Raster To Vector
• Satellite & Aerial– Land Cover: roads, forests, etc.– Buildings
• DEMs– Contours– Peaks & Valleys– Stream Networks– Watersheds
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Vector To Raster
• Drawing!
• Points of interest
• Roads
• Water bodies
• Contours
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GIS Analysis
AnalysisResults
Raster toVector
Vector toRaster
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Raster Analysis
• Topography: Slope, aspect, contours
• Raster Math
• Statistics: min, max, mean, std. dev.
• Distance
• Density
• Interpolation
• Classification
• Raster / Vector Conversions
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Raster Math
• A matrix of pixels
12 20 23 34 40
15 23 30 31 39
15 22 29 30 40
14 20 28 29 38
13 19 25 32 37
Columns
Rows
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Analysis Environment
• Spatial Reference (Coordinate System)– Make them the same
• Extent– Area of interest– All rasters should overlap
• Cell Size– Largest of all rasters or larger
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Common Functions
• Local:– Arithmatic: +,-,/, *,
• MOD (Modulo): returns the remainder
– Boolean: • OR: If either input is true, output is true• AND: If both inputs are true, output is true
– CON (Conditional)
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Mathematical Functions
• Abs (absolute): flips negatives to positive
• Ceil (ceiling): float to integer next highest integer value (i.e. 1.1 -> 2)
• Floor: float to integer giving next lowest integer value (i.e. 1.1 -> 1)
• Int (integer): truncates float to integer
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Exponents• Exp()• Exp10()• Ln()• Log10()• Max()• Min()• Pow()• SetNull()• Sqrt()• Sum()
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Comparisons
• <> (Not Equals)
• == (Equals)
• < (Less than)
• <= (Less than or equal to)
• > (Greater than)
• >= (Greater than or equal to)
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Raster Math: Comparisons
1 2
2 3
2 2
3 2
0 0
0 1> =
> =1 2 0
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Raster Math: Boolean AND
0 0
1 1
0 1
0 1
0 0
0 1AND =
AND =0 1 0
“AND” works but the calculator will insert “&”
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Raster Math: Boolean OR
0 0
0 1
1 1
0 1
1 1
0 1OR =
OR =0 1 1
“OR” works but the calculator will insert “!”
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Conditional Operator
• Con(<condition>,<true>,<false>)
• Given a raster “condition”:– Puts the true value where true and false
value where false
• Example:– Find the elevations in Rocky over 3000
meters– HighElevations=con(RockyDEM>3000,1,0)
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Viewshed
• Shows which “pixels” can be seen from pre-defined locations