Peer-review of the GED prototype in 1992 confirmed the need to ensure compatibility with GIS structures and processing functions, support for diverse user applications, a broadly based peer-review process, and the opportunity for direct interaction with data developers. GIS operability supports these goals by providing data in a common framework that bridges a range of similar systems sharing a common method of use. The benefits of GIS operability cannot be fully achieved (or tested in a quality control environment) through the use of common data exchange formats alone. Current efforts in the U.S. Government and elsewhere may eventually result in commonly accepted data transfer and interoperability standards. Even this, however, will not ensure suitable documentation and functional support for the wide range of applications desired of such computer databases.
A GIS integrates spatial and other kinds of information within a well defined database structure and provides software tools that can be used to manipulate and display geographical data-objects. Most GISs are graphically oriented, with display and map output capabilities ranging from cartographic displays, spatial imagery and 3-D overlays, to graphs and histograms of data or statistical investigations. Additionally, the integrated data structure and standardized "tool kit" of GIS functions provides useful capabilities to aid in data exploration, data intercomparison, spatial and temporal overlay studies, and more complex analyses of multiple datasets in space and time. One of the most important current areas for growth in GIS is error analysis - an important factor in the use of multi-thematic data combinations in analysis or modeling.
A GIS is a working environment representing an analytical philosophy that is established by the combination of geographical data and information objects (in the database) and an organized set of data management, analysis, exploration, and descriptive modeling tools. The introduction of GIS has revolutionized the way the scientific world views and manipulates geographical information. Of particular interest here are the advantages that GIS methods may provide for quality assessment and analysis of data, and for the derivation of useful information from static data modeling (data combinations and derivations).
GIS is a structured environment that is based on geographic (spatial/temporal) "entities," relationships between these entities (topology), and attributes (data and metadata) associated with them. The combined entity-attribute data object can be manipulated in the GIS with a wide variety of tools, some designed for data management and information retrieval, others designed more for spatial and temporal analysis and support for modeling. More than anything else, it is the geographic object definition and "intelligent" (topological and attribute-linked) data structures that define the GIS environment. Working within a GIS environment, one retains these linkages.
The two basic forms of data representation are vector (points, lines, polygon boundaries, lattices, and contours) and raster (cell or "grid"-based representation of the same object types as points, lines, areas, grids, and gradients). If properly employed both raster and vector data can be statistically equivalent, but the two forms offer different benefits. The possibilities for analytical modeling (statistical analysis, mathematical and logical overlay, spatial and time-series analysis, etc.) are greatest in a raster (cell-based) environment due to its simpler computational requirements in complex comparisons and overlays, and in representing or manipulating quantitative variables and their gradients. However data storage, retrieval, and display are often better handled in a vector system, especially for qualitative (classed) data. By representing datasets in both forms, useful visual comparisons can be easily performed, and the benefits of each form can be optimized.
After downloading the data to your PC, you can browse data in the GED using Idrisi by identifying the drive and path to a dataset directory in the Idrisi Environment, using the "ENVIRON" module. Data can be displayed with the DISPLAY module, data headers can be displayed with the DESCRIBE module, files can be LISTed, etc. In Idrisi for Windows, it is possible to display a data file, then change the environment to access another dataset, and plot vector overlays on the first (which is still in memory). In this manner datasets can be compared using the raster portion of one dataset and the vector portion of another. For example, the Micro World Databank (MW) boundary data can be plotted over any dataset to provide a geographic reference.
For users who wish to use Idrisi software to analize the contained datasets, a few simple procedures should be followed. First, create a working data directory on a hard drive with sufficient disk space to hold all data files you intend to use and files to be created. Then copy data from the website or CD-ROM (by dataset) into this common workspace. Finally, set the Idrisiw environment (using ENVIRON) to the working directory and begin work.
If the Windows or Windows 95/NT environment is not available, see instructions for using IDRISI for DOS (V4.x).
For more information, please contact Idrisi technical support.
There are currently two ways for UNIX/GIS users to access the contained datasets. The first is by access and export from a internet browser-equipped DOS workstation, using software provided on the GED or using the Idrisi software, if available.
The second option (if you have ordered the CD-ROM) is to access the CD-ROM directly from within the UNIX operating system and run UNIX software (as provided on with the GED or other) to perform the necessary conversion. This may require some programming experience, although NewForm software provided, using "format descriptor" files contained in the dataset directories, may be helpful in performing a major portion of the conversion work.
See GRASS Implementation, for further details.
Information about obtaining GRASS or support can be obtained from:
U.S. Army Corps of Engineers
Construction Engineering Research Laboratory
P.O. Box 4005
Champaign, IL. 61824-4005
Telephone: 1-800-USA-CERL ext 220
217-373-7220
Also, limited assistance is available from NGDC from:
David A. Hastings
Solid Earth Geophysics Division
National Geophysical Data Center
325 Broadway E/GC1
Boulder, CO 80303
email: dhastings@ngdc.noaa.gov
Web: http://www.ngdc.noaa.gov/seg/tools/sdts/grass.shtml
Tentative procedures for import to GRASS were written for GED Disc-A, and are included here with some updates.
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