Geographic raster data are commonly used for representing and managing imagery, digital elevation, and other phenomena which is widely used in hydrological research. A Geographic Raster resource is designed to support the sharing of raster datasets. A raster dataset can have a single or multiple bands (or layers) of data. A band is represented by a single matrix of cell organized into rows and columns where each contains a value representing information such as watershed elevation, temperature or precipitation.
In HydroShare, the GDAL Virtual (VRT) format is used to hold Geographic Raster content. GDAL (Geospatial Data Abstraction Library) is a widely used open source library used by geographic information systems for raster data. A GDAL Virtual (VRT) assembly must have one .vrt file and may have one or more raster files. In HydroShare we restrict the raster files to GeoTIFF files. The Virtual (.vrt) file is a description of the virtual dataset saved in an XML format that serves as an index to the component .tif or .tiff files. The GeoTIFF files are the actual tile raster data. VRT assembly’s allow a large raster dataset to be built up of smaller files, and our choice of this format was to avoid having to have large and sometimes unwieldy single files to represent large datasets. Click here to browse an example of a Geographic raster resource.