HTML Version 0.1 by Mike Fiorino, LLNL, 15 Jun 95
The Grid Analysis and Display System (GrADS) is an interactive desktop tool that is currently in use worldwide for the analysis and display of earth science data. GrADS is implemented on all commonly available UNIX workstations, CRAY UNICOS supercomputers (ymp, c90 and EL) and DOS-based PCs, and is freely distributed over the Internet.
GrADS provides an integrated environment for access, manipulation, and display of earth science data. GrADS implements a 4-Dimensional data model, where the dimensions are usually latitude, longitude, level, and time. Each data set is located within this 4-Dimensional space by use of a data description file. Both gridded and station data may be described. Gridded data may be non-linearly spaced; Gaussian grids and variable resolution ocean model grids are directly supported. The internal data representation in a file may be either binary or GRIB. Since each data set is located within the 4-D data space, intercomparison of disparate data sets is greatly facilitated. Operations may be performed between data on different grids, or between gridded and observational data. Data from different data sets may be graphically overlaid, with correct spatial and time registration.
The user accesses data from the perspective of the 4-D data model. A dimension environment is described by the user as a desired subset of the 4-D space. Data is accessed, manipulated, and displayed within this subset. Operations may be performed on the data directly, and interactively, by entering FORTRAN-like expressions at the command line.
A rich set of built-in functions are provided. In addition, users may add their own functions as external routines written in any language. The expression syntax allows complex operations that range over very large amounts of data to be performed with simple expressions. Once the data have been accessed and manipulated, they may be displayed using a variety of graphical output techniques, including line, bar, and scatter plots, as well as contour, shaded contour, streamline, wind vector, grid box, shaded grid box, and station model plots. Graphics may also be output in PostScript format for printing on monochrome or color PostScript printers. The user has wide control over all aspects of graphics output, or may choose to use the geophysically intuitive defaults.
A programmable interface is provided in the form of an interpreted scripting language. A script may display widgets as well as graphics, and take actions based on user point-and- clicks. Quite sophisticated data graphical interfaces can, and have, been built. The scripting language can also be used to automate complex multi-step calculations or displays. GrADS can be run in a batch mode, and the scripting language facilitates using GrADS to do long overnight batch jobs.
Acknowledgements and Disclaimer
We suggest new users go through the documentation chapter-by-chapter.
Appendix A: GrADS Data Sets
Appendix B: Scripting Language