NR 322: Raster Data

Jim Graham

Fall 2008

Chapter 7

Vector File Formats

• E00: Coverage exchange format– Decompress to get a coverage file

• KML: Keyhole Markup Language– Not georeferenced– Maybe with a prj file?

• STDS: US Government’s new vector format

Geo-Referenced Raster

• Known Projection and Datum

(X1,Y1)

(X2,Y2)

(X4,Y4)

(X3,Y3)

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)

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 calcualations

GeoReferenced File Formats

• GRID: ESRI’s format

• GeoTIFF: Excellent support

• MrSID: LizardTech

• IMG: ERDAS

• ECW: ERMapper

• BIL, BIP, BSQ: See header

• “ASCII” or “GRID ASCII”

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

• Maybe with a world file and prj?

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!)

JPEG

• Joint Photographic Experts Group

• Widest used photo format

• JPEG2000– Completely new format!– Can be georeferenced

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 -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

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

Contours

DEM Cross Section

2000m

1900m

2100m

2200m

Slope

Calculating SlopeDEM Cross Section

Aspect – Direction of the slope

Slope

Aspect (Direction)

Angle

Rise

Run

Slope = (Rise/Run) * 100%

Aspect

Hill-shade

This weeks lab

• Download DEM

• Create slope, aspect, hill-shade maps

• Make a map showing all 4 types

• How many scale bars do you need?

• How many legends to you need?