Glossary
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glossary
A,
B,
C,
D,
E,
F,
G,
H,
I,
J,
K,
L,
M,
N,
O,
P,
Q,
R,
S,
T,
U,
V,
W,
X,
Y,
Z
- adjustable array
- An array that is a dummy argument in a Fortran subroutine
or function whose dimensionality is determined at runtime.
The dimensionality of an adjustable array is supplied in the
argument list in which the dummy array name appears, or
by values in a COMMON block.
- animation
- A sequence of two or more images that, when displayed in a rapid
sequence, provide the illusion of continuous motion.
- annotation
- Any collection of elements of a plot whose behavior
can be controlled as a group.
- arithmetic operator
- An operator that applies to variables having a
numeric data type. Examples
are "+" (addition) and "*" (multiplication).
- ASCII file
- A file whose contents are to be interpreted as a sequence of
characters as defined by the ASCII (American Standard Code
for Information Interchange) standard.
- attribute
- A singly-dimensioned datum of any type that is assigned to
a variable using the '@' operator. An attribute of a variable
contains descriptive information about the variable.
- binary file
- A file whose contents are to be interpreted as a sequence of
bits, rather than characters.
There are different flavors of binary files. A "flat" binary
file is a sequence of bits with no ancillary information
about the file contents. This type of file is created and read
by C programs. Fortran creates and reads flat binary files
only when in direct-access mode.
All records are the same size in a flat binary file. By default,
Fortran creates another type of binary file which can contain
variable-length records. This is called a sequential-access
binary file. In a sequential-access binary file,
record length information is embedded prior to each record.
- block statement
- A statement that requires one or more individual statements
bracketed by delimiters indicating the beginning and end of
the block. Examples of block statements are: do-end do,
if-then-end if, setvalues-end setvalues.
- built-in function or procedure
- Functions and procedures that are part of the NCL language
and are automatically available.
- CCM history tape format
- A proprietary data format used by atmospheric climate
simulation models developed at NCAR. (CCM stands for
Community Climate Model.)
- C function prototype
- A C function declaration that declares a function's
return type, how many arguments the function takes, and
the types of the arguments.
- class
- A template for defining objects that specifies variables
and procedures that operate on those variables. In the
context of NCAR Graphics software, the class variables are
called resources and the class procedures are called
support functions.
- color map
(see color table)
- color table (also referred to as a color map)
- A table that associates integer values (called color indices)
with RGB color values. In NCAR Graphics,
color tables contain up to a maximum of 256 colors (including
the background color).
- comment line
- A line in an NCL code beginning with a semi-colon (;). A line
in an NCL resource file beginning with an exclamation point
(!). Comment lines contain descriptive information about
the code.
- contour plot
- A plot of 2D data containing contour lines (lines marking
points of equal elevation) to indicate surface shape. Contour
plots may have color fill between contour lines and may have
label bars and
annotations.
- coordinate addressing
- A way of indexing array elements by specifying coordinate
values rather than the normal integer array indices.
Coordinate addressing is effected by using
coordinate variables.
- coordinate array
- An array of coordinate values used for
coordinate addressing
with an associated
coordinate variable.
- coordinate variable
- A named dimension of an
array that has been assigned an
associated coordinate array
by use of the & operator.
- data type
- A qualifier on a variable that assigns it a specific
representation. In NCL the numeric data types are: double,
float, long, integer, short, and byte; the non-numeric
data types are: string, character, graphic, file, and
logical.
- decision statement
- A language construct allowing for conditional program
execution based on the truth or falsity of an expression.
The basic decision statement in NCL is if.
- file name suffix
- A suffix appended to a file name to indicate its type.
NCL recognizes the following supported suffixes:
".nc" for netCDF,
".hdf" for HDF,
".grb" for GRIB, and
".ccm" for CCM
History Tape. The obsolete suffix ".cdf" for a netCDF file is
also recognized.
- Fortran 90 interface block
- A sequence of Fortran 90 statements
(bracketed by special delimiting
statements) used to describe a procedure interface.
The statements in the interface block contain a declaration
for the procedure and
declarations for the dummy arguments and no executable
statements.
- GRIB
- GRids In Binary - a read-only
network-transparent
data format. GRIB is a format used by many of the world's
foremost operational weather centers. It is a very
space-efficient format.
- GSUN
- Acronym for "Getting Started Using NCL."
- HDF
- Hierarchical Data Format - a
network-transparent
and self-describing
data format developed at NCSA.
- High Level Utilities
- Objects, like XyPlot objects, Contour objects, TextItem
objects, and so forth, that can be created and manipulated
by a set of library functions, callable from either a C
program, a Fortran program, the NCAR Command Language, or
a GUI. High Level Utilities are also called HLUs.
- HSV
- Acronym for Hue/Saturation/Value. An additive color system
based on the attributes of color (hue), percentage of
white (saturation), and value (brightness or intensity).
- HLUs
(see High Level Utilities)
- interpreter
- A program that transforms statements into machine code a statement
at a time. The ncl executable is an interpreter of the NCL
language.
- irregular
rectangular coordinate space
- A 2-dimensional rectangular grid that has unequal spacing
along the X and/or Y axes.
- label bar
- A specialized label consisting of a bar of filled rectangular
areas that are labeled to correspond with areas from an
adjoining plot. Label bars can be filled with
black-and-white patterns,
with color, or with both. Label bars are commonly used
with contour plots and with other types of plots where
area pattern fills or color are used to differentiate
values in the plot.
- legend
- A specialized annotation that
formats a series of lines or
markers of varying styles along with adjoining explanatory
labels. Legends are designed to serve as "keys" for an
associated plot.
- loop statement
- A language construct that allows for code repetition with
incremental values set for a variable or variables. The looping
statements in NCL are: do and do while.
- logical operator
- A operator that returns a true value or a false value depending on
the truth or falsity of its operands. The logical
operators in NCL are: .and., .or., .xor., .not..
- machine-independent data format
- Same as Network-transparent
data format.
- metafile
- A file containing encoded graphical elements. Metafiles
are used for storing and transporting graphics images. In
the context of NCAR Graphics, "metafile" is generally
synonymous with "NCGM".
- metadata
- Ancillary information associated with an NCL variable.
There are three types of metadata: attributes, named dimensions,
and coordinates.
- missing value
- A special value for a variable or array element indicating
that no legal data has been specified for that quantity.
In NCL this is identified by the attribute _FillValue.
For details, see the section on
missing values in the
NCL Reference Manual.
- named colors
- A string containing the name of a color, like "HotPink".
Named colors can be used in place of color index values when
setting color resources. The file
"$NCARG_ROOT/lib/ncarg/database/rgb.txt"
contains a list of the valid color names.
- named dimension
- A dimension of a variable or file variable that has been
assigned a name using the '!' operator.
- NCL
- The NCAR Command Language, a programming language
designed specifically for the analysis and visualization
of data.
- ncl
- Refers to the
interpreter that interprets
NCL statements.
- NCGM (see metafile)
- NDC (Normalized Device Coordinates)
- A coordinate system that describes positions on a virtual
plotting device. The lower left corner corresponds to
(0,0), and the upper right corner corresponds to
(1,1). NDC space will be mapped onto the largest square
that will fit on an actual plotting device.
- netCDF
- The Network Common Data Format - a
network-transparent
and self-describing
data format developed at Unidata.
- network-transparent
data format
- A format for encoding data that removes any machine
dependencies that might be involved in encoding the data.
Typical examples of such data formats are
netCDF and
HDF.
- numeric data type
- A data type for numeric quantities.
In NCL the numeric data types are: double, float, long,
integer, short, and byte.
- non-numeric data type
- A data type for non-numeric quantities.
In NCL the non-numeric data types are: string, character,
graphic, file, and logical.
- object
- An instance of a class, formed by
assigning specific values to the variables in the class.
- output primitive
- A procedure for producing graphics output at the lowest
level. GSUN procedures exist for drawing lines
(gsn_polyline,
gsn_polyline_ndc),
text (gsn_text,
gsn_text_ndc),
filled areas (gsn_polygon,
gsn_polygon_ndc),
and markers (gsn_polymarker,
gsn_polymarker_ndc).
- primitive
(see output primitive)
- relational operator
- A operator that returns a true value or false value depending on
a relation between its operands. The relational
operators in NCL are: .le., .lt., .ge., .gt.,
.ne., .eq..
- resource
- A name that designates a particular attribute that will
affect plotting with NCL. Resources can be assigned
values. A couple examples of resources
are xyLineColors, used for defining line colors in an
XY plot, and cnLineLabelsOn, used for controlling
whether line labels appear on contour plots. There are
hundreds of legal resources.
- resource file
- A file that can be used to set values for resources.
- RGB values
- Stands for the red, green, blue color space where colors are
specified as triples of floating point numbers between 0.0 and
1.0 inclusive. The number triple gives the intensities for the
red, green, and blue components of a color. The RGB value
(1,.0.,0.) would indicate red, for example.
- script
- A file containing a sequence of program
statements that
can be submitted to an interpreter for execution.
- self-describing data format
- A format for encoding data that can contain information that
describes the data being encoded. Typical examples of such
data formats are
netCDF and
HDF.
- scalar variable
- A singly-dimensioned variable of size one.
- shape
- The number of dimensions of an array. The statement
a = new( (/ 2, 3, 5 /), float) would create an
array a of shape 3 (i.e. a has three
dimensions).
- size
- The number of elements in array dimensions. The statement
a = new( (/ 2, 3, 5 /), float) would create an
array a that has a first dimension of size 2, a
second dimension of size 3, and a third dimension of size 5.
- stipple
- To cover an area with small dots.
- streamline
- The path an idealized particle would follow if introduced
into a wind or fluid flow. For example (as an approximation
to the ideal), the path a speck of dust would take in a wind.
- Streamline plot
- A plot representing a vector field using
streamlines,
based upon 2-dimensional data. It may also contain tick marks and titles.
- stride
- The increment indicator in a subscript specifier. Using
m:n:i as a subscript means to take the individual
subscript values starting with m and ending with
n in strides of i. The stride must always
be an integer and should be thought of as a skip indicator
rather than an additive increment value, since coordinate
subscripts may not always be integers. A stride of 2 means
to take every second value after the first, a stride of 3
means take every third value, and so forth.
- statement
- A non-comment line of
code (or a line of code prior to any
commenting). A line of NCL code contains all continuations
resulting from use of the "\" symbol.
- supported data format
- Any of the formats that can be read by the NCL
addfile
function. The supported formats are:
netCDF,
HDF,
GRIB, and
CCM History Tape.
You do not have to know the details of these formats in
order to use them with NCL.
- tick marks
- Marks along an axis of a plot that are perpendicular to
the axis and serve to divide the axis (or parts of the
axis) into equal or logarithmetically spaced parts.
-
text function codes
- Special characters embedded in a
text string, usually starting and ending with the colon
(":") character. Text function codes provide the
capability for selecting various fonts, doing superscripts
and subscripts, taking complete control of the positioning
of characters relative to one another, and last but not
least, "zooming" characters in either width or height, or
both.
- variable
- A symbol that denotes an array, a dimension name, an
attribute, and so forth.
- Vector plot
- A plot representing a vector field by drawing glyphs that
represent magnitude and direction at grid points based on
2-dimensional data. It may also contain tick marks, titles, and/or a label bar. Three glyph styles are
available: a basic line-drawn arrow, a filled arrow with
an option edge, and a standard wind barb.
- viewport
- The viewport is a rectangular subregion of NDC space that specifies where the
graphics will be placed when drawn. The precise meaning of
the viewport depends on the type of graphic being
drawn. For example, for functions drawing XY plots (like
gsn_xy),
the viewport specifies where the grid containing the
curves will be placed, and the labeling (if any) will be
drawn outside of the viewport.
- workstation
- Used in NCAR Graphics Version 4 terminology to mean a valid
output device such as an X Window System display, a PostScript
file, or an NCGM.
- wrapit interface block
-
A sequence of Fortran 77 statements that specify a procedure
and its arguments, similar to C function prototypes and Fortran 90
interface blocks. Wrapit interface blocks are used by
wrapit77, a program for generating
wrappers.
- wrapper function
-
A C function that provides an interface between NCL and an
existing Fortran or C subroutine or function. The wrapper
intercepts an NCL function or procedure, does the appropriate
argument checks and conversions, then calls the existing code.
- XY plot
- A plot containing curves made up of X/Y coordinate
pairs. It may also contain tick marks,
titles, and/or a legend.
home |
toc |
about doc |
intro |
examples |
basics |
beyond basics |
hints and tips |
appendix |
glossary