Each block is stored as one variable-length record. Blocks are stored on disk in compressed form in a variable-length file structure referred to as a tile. Grids are implemented using a tiled raster data structure in which the basic unit of data storage is a rectangular block of cells. A multiple-band grid cannot have more than 9 characters in its file name, and a single-band raster dataset cannot have more than 13 characters. Caution:Īs with most formats, a grid should not be named with spaces or any other special characters in its name. Grids also carry additional information, such as the coordinate system associated with the grid. The coordinate system of a grid is thus defined by the cell size, the number of rows and columns, and the x,y coordinate of the upper left corner. Since each cell within a grid has the same dimension as other cells, the location and area covered by any cell is easily determined by its row and column. The rows and columns are parallel to the x- and y-axes of the coordinate system. The coordinate system of a grid is the same as that of other geographic data. An integer grid may have other INFO items added to its VAT whose range of values depends on the item definition. Integer grids can store values from -2147483648 to 2147483647 (-2 31 to 2 31-1).įor integer grids, this information applies only to the VALUE item.Floating-point grids can store values from -3.4 x 10 38 to 3.4 x 10 38.The range of data values that can be stored as grid values are as follows: For example, in a grid that represents elevation data in meters above sea level, a cell with a value of 10.1662 indicates that the location is about 10 meters above sea level. The cell value itself is the attribute that describes the location. The cells in this type of grid do not fall neatly into discrete categories. Learn more about raster dataset attribute tablesįloating-point grids do not have a VAT because the cells in the grid can assume any value within a given range of values. For example, if 50 cells have a value of 1 representing a forest, then the VAT would show a VALUE = 1 and COUNT = 50 for each of the 50 cells. The record stores the unique value (VALUE is an integer that represents a particular class or grouping of cells) and the number of cells (COUNT) in the grid represented by that value. A VAT has one record for each unique value in the grid. Learn more about discrete and continuous dataĪttributes for an integer grid are stored in a value attribute table (VAT). Use integer grids to represent discrete data and floating-point grids to represent continuous data. There are two types of grids: integer and floating point. A grid is a raster data storage format native to Esri.
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