This partially results from the fact that a raster file is only representative of individual cells or points that have been captured at one particular time given a data collection technique ( Kidner and Smith, 1993). Even in the case of high-resolution (small cell sizes) data sources, the data structure does not represent numerous attributes of the topography. Raster DTMs are static cartographic representations, which would require a large number of maps (data sets) to capture even the most basic changes to surface topography. Although compression techniques can be applied to help lower the storage volume ( Maune et al., 2007), there are no generally accepted compression methods.Ī main disadvantage of the raster data structure is that it does not conform to the ever-changing characteristics of the surface topography that reflect surface changes as well as internal structure of the landform or feature. A smaller storage size is ideal as it saves time and money to store and analyze the data ( El-Shrimy et al., 2005). A smaller cell size, however, generates larger file sizes ( Maune et al., 2007). A smaller cell size represents a higher resolution, creating a more detailed depiction of the surface area, compared to a larger cell size ( El-Sheimy et al., 2005). Breaking the surface down into tessellations permits information about a specific cell or area to be retrieved more efficiently, thereby reducing the processing time ( El-Sheimy et al., 2005).Įach grid cell contains its own specific value and the value only changes at the borders with an adjacent cell ( Maune et al., 2007). The grid is then divided up into smaller squares called tiles, which are divided up into blocks, and then cells, creating a grid pattern. Many other shapes have been used in place of squares. Tessellation shape can vary, however, and the choice of shape is dependent on a variety of other factors (e.g., distance calculations). The process of representing data in this structure is called a tessellation and is commonly represented as a square with similar x and y dimensions.
#RASTER DEFINITION SOFTWARE#
DTM mapping software stores data in the form of a ‘hierarchical tile-block structure’ that uses the grid cell as its foundation ( El-Sheimy et al., 2005).
Many current software packages possess algorithms to rapidly produce surface measures from raster datasets. Raster data are commonly used in geomorphology because they require less physical storage space. This simple data structure is based on a 2D matrix containing x and y coordinates, which are gathered at regular intervals to produce a grid pattern of square-shaped cells ( Kidner and Smith, 1993 El-Sheimy et al., 2005 Maune et al., 2007). Raster files are the most common data structure used by geomorphologists for terrain analysis. Oguchi, in Treatise on Geomorphology, 2013 3.6.3.3.1 Raster (grid)
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