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6 Geographic Information System (GIS) Components
This chapter introduces the Geographic Information System (GIS) functionality provided by AVS/Express.
Geographic Information Systems (GIS) is a branch of cartography and mathematics dealing with computer generated mapping and coordinate transformation systems. GIS can be readily applied to a variety of fields as diverse as geology, oceanography, demographics, planetary science, statistics, and finance.
The basis of GIS is to provide a common coordinate system to represent spatial data in a real world or planetary model. Information tends to represented as a latitude and longitude coordinate as well as an optional altitude component. Typical GIS applications render information that has a natural spatial component, such as oil and mineral detection or air traffic routing, into world model that already contains information in a geo- or planetary-centric view, such as a map of Colorado.
AVS/Express, provides most of the components necessary for importing and manipulating information in these real world models. Modules are provided for converting from (x,y,z) coordinate space to latitude, longitude, altitude coordinate space, as well as modules for transforming those coordinates from one cartographic representation to another. (Say, for instance, from mercator map projections to Albers map projections.)
Data can be passed into these modules in ways that are natural for AVS/Express users and developers: via existing data fields. Points, polylines or mesh data fields can easily be passed into one of the GIS transformation modules, and the resulting data field can be passed on to other, existing AVS/Express modules.
- Note: It is important that when importing (x,y,z) data into the GIS modules and macros that the following rule is remembered: When cartographers translate data to a cartesian plane, the meridian (longitude) values map to the x-axis, and the parallel (latitude) values map to the y-axis. Therefore, when passing (x,y,z) data into the GIS components, all components expect the ordering as (longitude, latitude, altitude). If you do not see the expected results while using the GIS components, this is the first item you should check.
AVS/Express also provides data readers for two widely used GIS data sets:
- The U.S. Geological Survey Digital Elevation Model (DEM) data sets, and the Central Intelligence Agency's World Databank II database. Both of these datasets are freely available on the Internet, or by ordering through the U.S. Government.
To learn more about Geographic Information Systems, there are two excellent references from the U.S. Geologic Survey. These references were extensively utilized in the creation of the AVS/Express GIS modules:
- "Map Projections Used by the USGS," Geologic Survey Bulletin #1532, John P. Synder, U.S. Government Printing Office.
- "Map Projections: A Working Manual," US Geologic Survey Professional Paper #1395, John P. Synder, U.S. Government Printing Office
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