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 GT or TS-formatted data set:
variable names, coordinates, units and pointers to the data files. Descriptor
file names normally end with ".DES".
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])".
Any disk data file that is readable by Ferret but is not in GT, TS, or
netCDF format.
FILE VARIABLE
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.
A file of Ferret commands intended to be executed as a single command with
the GO command.
A group of 1 to 4 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 file containing the definition of grids and axes — part of the GT and
TS formats.
GT FORMAT
"grids at time steps" format. A direct access format using a separate descriptor
file for descriptive metadata.
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.
Special formats created by the Thermal Modeling and Analysis Project (TMAP).
These formats use descriptor files to store information about the variables,
units, titles, and grids for the data. Separate formats allow optimized
access as time series (TS format) or as geographical regions (GT format).
As of Ferret version 2.30, netCDF is the suggested method of data storage.
TS FORMAT
"time step" format. A direct access format using a separate descriptor
file for descriptive metadata.
USER-DEFINED VARIABLE
A variable created with DEFINE VARIABLE (alias LET).
VARIABLE
Value defined on a grid.
VARIABLE NAME
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.
VARIABLE TITLE
A title string used to label plots and listed outputs of a variable.
VIEWPORT
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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