The world of RASTER data Modeling... Elevation....etc. The Spatial Analyst Extension

Two ways of looking at the world... The vector view...  All objects are made up of points, lines and polygons  All the shape files and coverages are vector files

The stained glass window, a vector representation of the world.

The tile mosaic: a raster representation of the world.

The raster view of the world...  All objects are made up of small cells (often squares) (this is called a tessellation)  Each grid cell can carry a only single piece of identifying information e.g. elevation or land cover or soil type or population density  Remote sensing data is raster based (the individual cells are called pixels)  Computationally simple... Most models are raster based

The raster attribute table...

Image Data  All image data are raster format  The cells carry digital number values that indicate brightness in a given part of the spectrum  The Digital Raster Graphics (DRG) file

The DRG is a scanned USGS topographic map. It is a TIFF file with an associated world file that provides spatial reference information

The TIFF file The “world” File

The world file must be in the same directory as the image for spatial registration to work. A TIFF world file is *.TFW a Mr. Sid Image world file is *.SDW, the world file for a JPEG is *.JPW... SO what do these numbers mean?

The transformation parameters are stored in the world file in this order: A D B E C F A = x-scale; dimension of a pixel in map units in x direction B, D = rotation terms C, F = translation terms; x,y map coordinates of the center of the upper-left pixel E = negative of y-scale; dimension of a pixel in map units in y direction Note The y-scale (E) is negative because the origins of an image and a geographic coordinate system are different. The origin of an image is located in the upper-left corner, whereas the origin of the map coordinate system is located in the lower-left corner. Row values in the image increase from the origin downward, while y-coordinate values in the map increase from the origin upward.

More Image data....the DOQQ  Digital Ortho Quarter Quads (DOQQ)  Pan-chromatic aerial photography has been scanned, corrected for tonal differences, referenced to map space, projected to UTM and made available by the USGS  GeoTIFF format is available.... The spatial reference information is stored in the TIFF header

The GeoTIFF Header file

Mr.Sid?  What is a SID file? MrSID is an acronym for Multi-resolution Seamless Image Database. MrSID is a powerful wavelet based image compressor, viewer and file format for massive raster images that enables instantaneous viewing and manipulation of images locally and over networks while maintaining maximum image quality  

Some places have DOQ data available for download......

A neat trick in arcview.... Go to the legend editor for the DRG. Choose the colormap and change specified colors to transparent...

Oops! Note the offset...this is diagnostic of a datum shift between NAD 27 and NAD84

A better example of combining DRG with another Image

Finding and using DEM data  DEM data was developed as an offshoot of the cruise missile program...  The ‘brain’ of a cruise missile has to be able to ‘see’ the landscape and compare it to an data set stored in its memory... A digital elevation model  Each cell carries elevation data

Continuous Raster Data: the Digital Elevation Model (DEM)

GIS Data Depot: DEM, DRG of the US.

A variety of data are available: lets look at the processes needed for acquiring and displaying a DEM

The file identifier Digital Elevation Model SDTS (spatial data transfer standard): “I’m from the Government and I’m here to help you!” “TAR”... A UNIX command used to transfer an entire directory to a new location Gnu Zip... A free compression utility

Virtually all compression/decompression programs e.g. WinZip know how to handle *.TAR.GZ files

The Spatial Data Transfer Standard (SDTS) “The purpose of the SDTS is to promote and facilitate the transfer of digital spatial data between dissimilar computer systems...” f5.er.usgs.gov/sdts/articles/pdf/senmgr.pdf f5.er.usgs.gov/sdts/articles/pdf/senmgr.pdf The guidebook for “senior managers”... Should come with cartoons and short words....

While there are a variety of SDTS file converters, I prefer SDTS2DEM.exe: as this program is no longer easy to find, I have placed a copy on my web site www2.una.edu/gggaston

SDTS2DEM  A simple DOS based executable  Must reside in the same directory as the SDTS files  You CANNOT have ANY spaces in file names or directories!  e.g. “My Documents”  Use_the_underscore_character_to_divide_ file_or_directory_names

Ready to convert SDTS to a standard USGS DEM format that can be used in the GIS program. Note the lack of spaces in the path/filenames and the SDTS2DEM program

The first four characters of the base name are numbers The output is the DEM file that gets written L0... Just type it...it always works

All these Have become this

In Arcview 3.X you must activate the spatial analyst extension

The SDTS2DEM converts the SDTS format to a standard USGS DEM format, it is necessary to then import that file into arcview:

The DEM can now be used in Arcview, a nice trick is to create a hillshade of the data and use it as a brightness theme:

Hypsometric tinting with Shaded relief as brightness theme: