ABSTRACT EXPRESSION (or VARIABLE)
An expression which contains no dependencies on any disk-resident data is referred to as "abstract". For example, SIN(x), where x is a pseudo-variable.
A line along one of the dimensions of a grid. The line is divided into n points, or more precisely, n grid boxes where each grid box is a length along the axis. Adjacent grid boxes must touch (no gaps along the axis) but need not be uniform in size (points may be unequally spaced). Axes may be oriented (e.g. latitude, depth, ...) or simply abstract values.
A profile for the standardization of netCDF files.
The information needed to obtain values for a variable: the location in space and time (points or ranges), the name of the data set (if a file variable) and an optional grid.
A collection of variables in one or more disk files that may be specified with a single SET DATA command.
A file containing background data about a multi-file data set: variable names, coordinates, units and pointers to the data files. Descriptor file names must end with ".DES" or ".des", or beginning with Ferret v6.85, may end in ".mc", ".MC", or a file may be designated as a descriptor file with SET DATA/FORMAT=descriptor.
An axis that is inferred through the use of lo:hi:delta notation. It is created and destroyed dynamically by Ferret.
A grid whose axes are inferred from a regridding operation that does not explicitly specify all of the destination axes or specifies a destination grid that can be rendered conformable with the originating grid only if some axes are removed or substituted.
Any valid combination of operators, functions, transformations, variables and pseudo-variables is an expression. For example, "ABS(U)", "TEMP/(-0.03^Z)" or "COS(TEMP[Y=0:40N@LOC:15])".
EZ DATA SET
Any disk data file that is readable by Ferret but is not in GT, TS, or netCDF format.
A variable made available with the SET DATA command. File variables are data in disk files suitable for plotting, listing, using in user-variable definitions, etc.
The "Graphical Kernel System" - a graphics programming interface that facilitates the development of device-independent graphics code.
GO FILE or GO SCRIPT
A file of Ferret commands intended to be executed as a single command with the GO command.
A group of 1 to 6 axes defining a coordinate space. A grid can associate the axes as "outer products" creating a rectangular array of points. Grids may be defined with the DEFINE GRID command or from inside data sets.
A length along an axis assumed to belong to a single grid point. It is represented by a box "middle", a box upper and a box lower limit. The "middle" need not actually be at the center of the box but the upper limit of box m must always be the lower limit of box m+1. (This concept is needed for integration of variables along an axis.)
A representation of graphics stored in a computer file. Such a file can be processed by an interpreter program (such as Fprint) and sent to a graphics output device.
An axis where the first point of the axis logically follows the last. Examples of this are degrees of longitude or dates in a climatological year.
A regridding operation where the destination axis is modulo and the regridding transform is a modulo operation. Typical usage would be to create a 12-month climatology from a multi-year time series.
Network Common Data Format is an interface to a library of data access routines for storing and retrieving scientific data. NetCDF allows the creation of data sets which are self-describing and network transparent. As of Ferret version 2.30, NetCDF is the suggested method of data storage.
A function that is syntactically expressed in-line instead of as a name followed by arguments. The Ferret operators are +, -, *, /, ^, AND, OR, EQ, NE, LT, LE, GT and GE.
A special variable whose values are coordinates or coordinate information about a grid. X, I, XBOX, XBOXLO and XBOXHI are the pseudo-variables for the X axis - similarly for the other axes.
Commands and variable names may require auxiliary information supplied by qualifiers. In the command "SHOW DATA/FULL," "/FULL" is a qualifier. In the variable "SST[Y=20N]," "Y=20N" is a qualifier.
The location in space and time (or other axis units) at which a variable is to be evaluated. The locations may be points or ranges. For example, T="1-JAN-1982",Y=12S:12N describes a region in latitude and time.
The process of converting the values of a variable from one grid to another. By default this is done through multi-linear interpolation along all axes from the old grid to the new. Other methods are also supported.
A coordinate system for referring to grid locations in which the points along an axis are regarded as integers from 1 to the number of points on the axis. The qualifiers I, J, K, and L are provided to specify locations by subscript.
An operation performed on a variable along a particular axis and specified via the syntax "@trn". Some transformations, such as averaging (e.g. U[Z=@AVE]), reduce the range of the variable along the axis to a single point. Others, such as taking a derivative (e.g., V[T=@DDC]) do not.
A variable created with DEFINE VARIABLE (alias LET).
Value defined on a grid.
The name by which a variable will be indicated in commands and expressions. Names begin with letters and may include letters, digits, dollar signs, and underscores.
A title string used to label plots and listed outputs of a variable.
A graphical display region which may be any subrectangle of a window. Graphical commands (PLOT, CONTOUR, etc.) take complete control of a viewport, clearing it as needed. A window may contain several viewports - possibly overlapping. Viewports are defined with DEFINE VIEWPORT and controlled with SET and CANCEL VIEWPORT.
A rectangular graphical display region. On a graphics terminal the terminal screen is the one and only window available. On a graphics workstation there may be many output windows.
A coordinate system for referring to grid locations in which the points along an axis are regarded as continuous values in some particular units (e.g., meters of depth, degrees of latitude). The qualifiers X, Y, Z, and T are provided to specify locations by world coordinate.
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