Examples of Geospatial Tools Downloaded Off the Internet
Digital elevation models (DEMs) were acquired from the GIS Data Depot (www.gisdatadepot.com), and were in Spatial Data Transfer Standard (SDTS) format. The data were first downloaded in compressed format, and then uncompressed with compression software. Next, all 20 *.ddf files were converted with the use of SDTSEDEM.EXE, which is freeware that was created by Sol Katz of the BLM in Denver, Colorado, and
was acquired from the United States BLM FTP site. This executable converts all the various
DEM components into one usable DEM file. Next, the *.DEM file was imported into IDRISI32 with the DEMIDRIS module, and the finished product is viewable within IDRISI in raster format.
Click on the links below to View sample DEMs for the study area:
Sheep Peak Quadrangle, Culberson County, Texas (31104b8, source USGS).
Nutt Ranch Quadrangle, Culberson County, Texas (31104b7, source USGS).
EarthExplorer Aerial Photos (Digital Orthophoto Quadrangles)
For quick views of a potential study area, browse images from Earth Explorer (replaced GLIS)
are good enough quality to at least become familiar with an area, and higher-quality
DOQs can be ordered from the USGS. DOQs from the Sheep Peak Quadrangle and the Nutt Ranch
quadrangle are included below.
Browse image Digital Orthophoto Quadrangle of the Sheep Peak SE Quadrangle, Culberson County, Texas, (source: USGS EarthExplorer).
Browse image Digital Orthophoto Quadrangle of the Nutt Ranch SW Quadrangle, Culberson County, Texas, (source: USGS EarthExplorer).
Digital Raster Graphics (DRGs)
Click Here for full-size image (Scale: 1:48000).
This mosaiced DRG from the USGS was downloaded from the GIS Data Depot. A DRG is basically just a scanned-in USGS 1:24000 7.5' topo sheet, and in this instance, two DRGs are mosaiced together to show the Tumbledown Mountain study area. The DRG on the left is the Sheep Peak, Culberson County, Texas map (#31104b8) and the DRG on the right is Nutt Ranch, Culberson County, Texs DRG (#31104b7). (For project purposes, the DRGs were reduced to a scale of 1:48000 to adequately show the study area, and to keep image image size within a workable range). The two images were cropped in Adobe Photoshop 5.0, spliced together, and then saved as one resultant image.
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