Raster data models |
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Release 9.1
Last modified April 29, 2005 |
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There are two main raster data models: the raster dataset and the raster catalog.
Raster datasets are composed of one or more raster dataset bands. A raster dataset band is a rectangular matrix of cells. There are two types of raster datasets, the single band raster dataset and the multiband raster dataset. An example of a single band raster dataset would be a digital elevation model (DEM). A DEM contains values of elevation, of which there is only one value per cell. You can also have a single band orthophoto, which is sometimes called a panchromatic or grayscale image. When there are multiple bands (the multiband raster dataset), then every pixel location has more than one value associated with it. For example, a satellite image commonly has multiple bands representing different wavelengths—from the ultraviolet through the visible and infrared portions of the electromagnetic spectrum. Landsat 7 imagery, for example, collects data from eight different bands of the electromagnetic spectrum. Bands 1–5, 7, and 8 represent data from the visible, near infrared, and short-wave infrared regions (band 8 is also collected at a higher resolution). Band 6 collects data from the thermal infrared region. Another example of a multiband image is a true color orthophoto, where there are three bands, each representing either red, green, or blue light.
Learn more about supported raster formats
Learn how to create a raster dataset in a geodatabase
Raster catalogs are a collection of raster datasets organized in a table, in which the records define the individual raster datasets included in the catalog. They are used to display multiple, adjacent, or overlapping raster datasets without having to merge or mosaic them into one larger file, and they can contain multiple raster types, formats, resolutions, and file sizes. Raster catalogs can exist as file-based tables or in a geodatabase.
To create a file-based raster catalog, any table format can be used; the only requirement is that the table contains five columns: IMAGE, XMIN, YMIN, XMAX, and YMAX. The IMAGE column must contain a full path, relative path, UNC path, or an environment variable indicating where a raster dataset is located. When a relative path is used, it is relative to the table's location. The remaining columns describe the extent of the raster dataset.
View an illustration of a text file that defines a raster catalog
There are two main steps when creating a raster catalog in a geodatabase: Create the empty raster catalog in the geodatabase and load the raster datasets into the new raster catalog.
Learn more about creating geodatabase raster catalogs