NR 422: Raster Analysis Jim Graham Spring 2010

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

Categorical vs. Continuous

“No-Data” or NULL Values Rasters are always rectangular No-Data values are “transparent” and are not used for calculations

Geo-Referenced Raster Known Projection and Datum Width and height of a pixel in map units (X1,Y1) Width in Pixels Height in pixels

Geo-Referenced Raster Known Projection and Datum (X1,Y1) (X3,Y3)

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!

Digital Raster Graphic

Digital Elevation Model (DEM)

Hill-shade

Contours

DEM Cross Section 2000m 1900m 2100m 2200m

Slope

Calculating Slope DEM Cross Section

Aspect – Direction of the slope Slope Aspect (Direction) Angle Rise Run Slope = (Rise/Run) * 100%

Aspect

Hill-shade

Creating a Hillshade Obtain a DEM Crop to Desired Area Create Hillshade Apply color ? To DEM Add DEM over Hillshade with Transparency

Screen shots: –Hillshade dialog –Colorizing dems –Transparency

Spatial Analyst Extension Make sure “Spatial Analyst” is Checked

Tool Bar Right-click in the menu area Select “Spatial Analyst”

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

“Colorize” the DEM

Make the Hillshade Transparent

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

“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)

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

Not Geo-Referenced BMP PNG GIF JPEG Maybe with a world file and prj file?

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

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!)

GRIDS ESRI’s native raster format Pyramids Not an exchange format!

ASCII format NCOLS 10 NROWS 9 XLLCORNER 1000 YLLCORNER 1000 CELLSIZE 1 NODATA_VALUE Etc. See example

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!

Derived Rasters Land Cover from satellite and aerial Topography: Slope, aspect, hillshade Ecoregions Suitable Habitat Flood plains Geological Regions

Raster To Vector Satellite & Aerial –Land Cover: roads, forests, etc. –Buildings DEMs –Contours –Peaks & Valleys –Stream Networks –Watersheds

Vector To Raster Drawing! Points of interest Roads Water bodies Contours

GIS Analysis Analysis Results Raster to Vector Vector to Raster

Raster Analysis Topography: Slope, aspect, contours Raster Math Statistics: min, max, mean, std. dev. Distance Density Interpolation Classification Raster / Vector Conversions

Raster Math A matrix of pixels Columns Rows

Spatial Analyist

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

Spatial Analyst: General

Spatial Analyst: Extent

Spatial Analyst: Cell Size

Raster Calculator

Raster Math = +=11213

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)

Mathematical Functions Abs (absolute): flips negatives to positive Ceil (ceiling): float to integer next highest integer value (i.e > 2) Floor: float to integer giving next lowest integer value (i.e > 1) Int (integer): truncates float to integer

Exponents Exp() Exp10() Ln() Log10() Max() Min() Pow() SetNull() Sqrt() Sum()

Comparisons <> (Not Equals) == (Equals) < (Less than) <= (Less than or equal to) > (Greater than) >= (Greater than or equal to)

Raster Math: Comparisons > = >=120

Raster Math: Boolean AND AND = =010 “AND” works but the calculator will insert “&”

Raster Math: Boolean OR OR = =011 “OR” works but the calculator will insert “!”

Conditional Operator Con(,, ) 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)

Elevations over 3000 meters

Viewshed Shows which “pixels” can be seen from pre-defined locations

View-shed

View from Estes Park

View from Ridge