 A
raster divides spaces into uniform cells or pixels and uses a 2-D matrix to store sampled values for each cell. Each cell has the same width and height. The cells
in such a raster dataset can depict a variety of data such as the reflectance of light for part of the spectrum in a satellite image, a color value for a photograph,
a thematic attribute such as vegetation type, a surface value, or elevation. Raster datasets can represent an imaged map, a surface, an environmental attribute sampled
on a grid, or photographs of objects referenced to features.
In the context of GIS applications, raster data is an abstraction of the real world where spatial data is expressed as a matrix of cells or pixels, with spatial
position implicit in the ordering of the pixels. With the raster data model, spatial data is not continuous but divided into discrete units. This makes raster data
particularly suitable for certain types of spatial operations, such as overlays or area calculations. Unlike vector data, however, there are no implicit topological
relationships.
The ArcSDE 9.2 Raster API provides a mechanism for loading raster data from
an application onto the ArcSDE server and retrieving it. The API is low-level interface for basic
read-write raster data access to the ArcSDE server. Thus, it enables
organizations to store their raster data in any
commercial (IBM DB2, Informix, Microsoft SQL Server, and Oracle) relational DBMS
for fast, online, multi-user access to continuous raster data.
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