McIDAS Programmer's Manual
Version 2003
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Miscellaneous, 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
alias
A
short, user-defined name representing an ADDE dataset name; for example,
the alias GV1 could represent the dataset name
SSEC-RT/GOES8-1KVIS.
ancillary data
Additional
information needed to identify, quantify and manipulate data; for example,
directory, navigation and calibration blocks.
API
Application
Program Interface.
applications program
A
program that runs from the McIDAS-X command line.
area
The
McIDAS-X image file format.
ASCII file
American
Standard Code for Information Interchange file containing only text; for
example, schema definition files and scripts.
asynchronous
McIDAS-X
commands that run asynchronously will return control to the original calling
program before they have run to completion. Also see synchronous.
band map
Region
of the line prefix that contains an ordered list of the spectral bands comprising
the data portion of an image line.
big-endian
Used
interchangeably with network-byte-order to mean the most significant byte
in a word comes first; opposite of little-endian where the least significant
byte comes first.
binary file
A
file containing binary information; for example, areas and executable programs.
blank-padded
Describes
the practice of replacing unused characters at the end of a string with spaces.
block
A
collection of data records.
blow down
To
decrease image resolution by sampling or averaging data. For example, a blowdown
of two drops out every other data point along the line and every other line
in an image.
blow up
To
increase image resolution by replicating data point values, much like enlarging
a 3 x 5 photograph to an 8 x 10.
byte
An
8-bit memory segment; a 16-bit memory segment is called a half-word; a 32-bit
memory segment is called a word.
calibration block
The
image object block that holds the information for transforming image data
from its internal quantities to more common physical quantities, such as
radiance or albedo.
calibration module
A
group of subroutines that are specific to a type of image data; this module
is used to perform a calibration.
celestial coordinates
Identical
to earth coordinates except the x-axis passes through the longitude of vernal
equinox rather than the prime meridian so that the celestial system is fixed
relative to the stars. The transformation from celestial to terrestrial involves
a single axis rotation about the z-axis, equivalent to a scalar shift in
longitude. Satellite orbital predictions are typically made in a celestial
system.
client
The
workstation in a distributed system that initiates a request, then receives
and displays the requested data.
client routing table
The
table that holds the list of group names configured by the user with the
McIDAS-X DATALOC command.
clipping region
See viewport.
command line
The
command or series of commands entered in the McIDAS-X Text and Command Window.
It may consist of positional parameters, keywords and quoted text. In McIDAS-X,
the number of characters permitted in a command line is workstation dependent,
although there is no practical limit.
comment block
An
image object block containing a variety of textual information, such as a
list of commands run on the image object to-date.
compatibility
library
A
file where obsolete McIDAS-X library functions are placed for one year when
they are no longer referenced by any core programs. Also see local
library and McIDAS-X library.
conformal
projection
A
map projection in which angles are preserved; for example, parallels of latitude
and meridians of longitude intersect at right angles. McIDAS-X supports Mercator,
Lambert conformal, polar stereographic and tangent- cone conformal projections.
connection
The
initialization that occurs in a distributed system when a client determines
the location of the dataset server and issues a request for a data exchange.
The server examines the request and determines its validity; if the request
is valid, the connection is opened and the client is authorized to begin
its transaction.
contrast
stretching
The
process of changing an image's gray scale to emphasize a feature for analysis;
for example, thunderstorm cloud tops. Unlike data stretching, contrast stretching
does not change the image data values.
coordinate systems
The
four systems used to define the location of data points within an image;
they include image, file, earth and frame coordinates. A fifth coordinate
system, called world coordinates, is used with graphics.
cursor
The
mouse-driven, highlighted mark that appears on the McIDAS-X display. Users
manipulate the cursor to interact with McIDAS-X commands and the McIDAS-X
Image Window. Several cursor sizes, types and colors are available.
data point
A
collection of one or more bytes.
data point size
The
number of bytes needed to accurately represent a data point; usually 1, 2
or 4 bytes.
data stretching
The
process of changing an image's gray scale by stretching image data values
to brightness values. To stretch image data values, a table defining the
values to stretch must be created with the McIDAS-X SU command.
dataset
A
collection of one or more files with a common format; for example, one dataset
may contain image data, while another dataset may contain point data.
dataset name
The
name used by the ADDE server to identify the type of data the user wants
to access and the range or names of files to search. It consists of a group
name and a descriptor name separated with a slash, such as SSEC-RT/GOES8-1KVIS.
decoder
The
software that parses data from one format into a common format for use by
another process such as a plotter or lister, or software that further manipulates
data.
default
The
parameter value accepted by the program if the user doesn't specify a value.
To use the default for a positional parameter, the user types the letter
X in the command line.
descriptor
The
name used to reference a dataset in ADDE; for example, a dataset of images
containing GOES-7 visible data at 4-km resolution might have the descriptor
G7-VIS-4K.
directory block
An
image object block containing the list of ancillary information about the
image, such as the number of lines and data points, the satellite ID and
the number of spectral bands.
disk file
McIDAS-X
file for storing information that applications can randomly access by byte
address using standard system library calls. Formerly called LW (Large Word)
array files.
display
The
device used to output image and graphical data in McIDAS-X; usually a workstation
monitor or an X Terminal.
distributed data system
A
computing system in which data is received, processed and stored, and then
distributed among multiple workstations. Data can be received and processed
on the same machines that store and serve it.
DLL
Dynamic
Link Library; the library used in dynamic linking. OS/2 has true dynamic
linking, while Unix modules are statically linked only giving the appearance
of dynamic linking.
double precision
A
two-word storage representation for floating-point numbers.
element
The
image coordinate that makes up each division of the image along a scan line.
Elements run vertically up and down the frame; they are numbered left to
right with the leftmost element numbered one.
environment
The
place where applications programs reside, along with McIDAS-X resident programs
and shared memory.
equal-area
projection
A
projection in which areas are preserved; two equal areas on the Earth are
also equal on the projection, even though their shapes are different. McIDAS-X
supports the sinusoidal equal-area projection.
extended format
McIDAS-X
commands run with an extended format can contain a semicolon, indicating
the start of a sequence of commands, or one or more pound signs, indicating
a required string substitution.
file redirection
The
process that lets users identify the location of individual files on a workstation.
format
File
format. McIDAS-X file formats include image, grid, point and text; non-McIDAS-X
formats include HDF and NetCDF.
frame
Contains
a representation of an image sector displayed on the McIDAS-X Image Window.
Users can define the number and size of frames; the default is four frames
that are 480 lines by 640 elements.
frame coordinates
The
native coordinates of a frame referenced sequentially by lines and elements.
The frame's upper-left corner has coordinates (1,1). The number of lines
and elements on the frame is determined by the frame size.
frame object
A
memory-based collection of information that completely describes the contents
and appearance of a frame to the mcimage process, which realizes it into
a visible picture. Frame objects are stored in McIDAS-X shared memory.
FTP
File
Transfer Protocol. A method of transferring files between workstations on
a network.
full image
The
entire image transmitted by a sensor source.
full resolution
One
image data point represents one satellite sensor data point. Also see image
resolution and satellite resolution.
function
The
term used in this manual to describe C procedures and functions, and Fortran
functions and subroutines.
geodetic latitude
The
angle between a line perpendicular to the surface of the geoid through a
point and the Earth's equatorial plane. Due to the Earth's oblateness, geodetic
latitudes (the most common form of earth location) are slightly greater than
geocentric latitudes except at the equator and poles where they are identical.
geoid
The
spheroid (surface formed by rotating an ellipse about the polar or Z-axis
of the terrestrial coordinate system) that most closely approximates the
Earth's surface.
geostationary satellite
A
satellite that remains above a fixed location on the Earth's surface, usually
about 36,000 km above the equator. It is limited in view, approximately 60° either
side of the equator. GOES-8 and -9 view North America; Meteosat views Europe
and Africa; GMS views the western Pacific.
global keyword
A
keyword that can be used with any McIDAS-X command.
global string
A
string name whose first character is a question mark; useful for defining
strings that you don't want accidentally deleted. Global strings remain in
the string table even if the current string table is replaced with another.
GMS
Geostationary
Meteorological Satellite.
GOES
Geosynchronous
Operational Environmental Satellite.
graphics
Text,
symbols and line segments drawn in color on the McIDAS-X Image Window.
gray scale
The
range of black-to-white gray shades available for displaying image data on
the McIDAS-X Image Window. The range is 0 (black) to 255 (white).
gray shading
The
most common method of displaying image data.
grid
A
lattice of regularly spaced data points superimposed on a projection of the
Earth. Grids are generated from numerical models or observational data.
grid header
The
part of the grid object that contains the ancillary information about the
grid, such as the parameters and physical quantities of the data in the grid,
the level in the atmosphere or ocean the data represents, the grid navigation
information and the time.
grid object
The
actual gridded data along with the ancillary information contained in the
grid header.
group name
In
ADDE, the name used by the client to identify the server machine to get the
data from. The server uses it to identify the data that the client is requesting.
handle
A
computer term used to describe a variable in a program that points to a specific
structure. Handles are often used with input and output events.
help
A
block of comments describing an applications purpose, its positional parameters
and keywords, and other notable remarks.
image coordinates
The
native coordinates of remotely sensed data expressed as lines and elements.
Each image is a series of lines and elements arranged from top to bottom,
forming a grid for displaying data points on a McIDAS-X frame. Lines run
horizontally across the frame; elements run vertically up and down the frame.
The top line and leftmost element have the image coordinates (1,1). This
coordinate system is independent of McIDAS-X and forms the basis for other
McIDAS-X coordinate systems.
image object
The
actual image along with its ancillary data.
image object block
A
collection of image objects; each block contains image data or ancillary
information.
image resolution
The
number of satellite scan lines represented in each data point of an image
line. Resolution can be increased or decreased; see blow
up and blow down. Also see full
resolution and satellite resolution.
image sector
A
rectangular subset of a full image with the same coordinate system.
Image Window
The
window used for displaying frames containing McIDAS-X-generated images and
graphics.
include files
Files
that hold definitions of constants specific to the McIDAS-X software; for
example, mcidas.h and fileparm.inc.
ingestor
A
process that listens to data received by a communications port and reformats
the information for further processing.
interface documentation block
The
template to use when writing a new McIDAS-X library function in Fortran or
C.
line prefix
Optional
information that precedes the data on an image line; contains ancillary data
about the line, such as navigation or calibration parameters.
line prefix block
The
image object block containing information about an image that may vary on
a line-by-line basis, such as documentation or calibration information.
little-endian
The
least significant byte in a word comes first; opposite of big-endian where
the most significant byte comes first.
local library
A
file for keeping your local functions with their application's source code.
A local library is useful for referencing functions that SSEC moves to the
compatibility library. Also see compatibility
library and McIDAS-X library.
lock
A
unique, alphanumeric name (usually a legal file name) used to ensure that
two programs can't access the same resource simultaneously.
looping
Continuous,
automatic stepping through a sequence of image and/or graphics frames, much
like a movie loop.
makefile
A
description file that defines the relationships or dependencies between applications
and functions; it simplifies the development process by automatically performing
tasks necessary to rebuild an application when you modify code.
map files
Outlines
of political or geographic boundaries that can be superimposed on the McIDAS-X
Image Window using the MAP command.
McIDAS
Man
computer Interactive Data Access System; a collection of tools for acquiring,
analyzing and displaying meteorological data, created by the Space Science
and Engineering Center of the University of Wisconsin-Madison. McIDAS-X runs
on Unix workstations.
McIDAS-X library
A
file called libmcidas.a that contains all the
object code for the functions and subroutines that make up the McIDAS-X Application
Program Interface (API). Also see local library and compatibility
library.
McPATH
The
environment variable in McIDAS-X that defines directories for commands to
search when looking for data and help files.
memory overflow
Writing
beyond the memory allocated for a variable.
Meteosat
European
geosynchronous meteorological satellite.
mouse
See pointing
device.
navigation block
A
McIDAS-X data structure containing the projection type and set of parameters
for computing transformations between earth and image coordinates. Sometimes
called a navigation codicil.
navigation module
A
group of subroutines that are specific to a type of image data; this module
is used to perform navigation.
navigation transform
A
set of equations for converting a dataset's image or grid coordinates to
and from earth coordinates.
network-byte-order
See big-endian.
null-terminated
Describes
the practice of placing a zero (ASCII NULL character) at the end of a character
string; this is the standard representation in the C language.
pipe
Shared
space that accepts the output of one program for input into another.
pixel
A
point on a McIDAS-X frame assigned a unique pair of line and element coordinates.
POES
Polar
Orbiting Environmental Satellite.
point object
The
actual point data values along with their ancillary information.
point data
Atmospheric
or oceanographic data occurring at irregularly spaced locations on the Earth
or vertically within the atmosphere or ocean. Most data gathered by direct
measurements, such as weather balloons and synoptic reports, is stored as
point data.
pointing device
A
three-button mouse; the leftmost button is used by the window manager and
the middle and right buttons are used by the McIDAS-X mouse interface.
polar orbiting satellite
A
satellite that provides complete coverage of the Earth's surface twice per
day. It normally orbits 800 to 900 km above the Earth and has a field of
view that is about 2400 km, centered on the orbit path.
position
In
ADDE, the absolute or time-relative position of a file in a dataset; position
numbers greater than zero represent an absolute position in the dataset;
numbers less than or equal to zero represent a relative position, 0 is most
recent and -1 is next most recent; for example, if a dataset has four images
with times 13, 14, 15 and 12, they have the positions -2, -1, 0 and -3.
positional parameters
Alphanumeric
values that provide input to a McIDAS-X command; they must be entered in
the exact order specified. Useful for minimizing the number of keystrokes
a user types.
physical
quantity
Radiance,
temperature, albedo, etc.; sometimes, in error, called unit.
process chain
A
series of processes run synchronously.
projection
A
set of equations relating earth locations (three variables) to a location
in Cartesian coordinates on the projection plane. Also see conformal
projection, equal-area projection and earth
coordinates.
projection parameters
One
or more constants contained in projection equations; specifying values for
these constants defines an instance of the projection.
pseudo-Mercator projection
A
projection in which latitude and longitude vary uniformly with line (or row)
and element (or column). This projection is distinct from a true Mercator
and is neither conformal nor equal-area.
real-time data
Data
that is available to users as soon as it is received by the system.
redirect tables
Part
of the shared memory block that resides in the McIDAS-X environment; file
redirection information from the McIDAS-X REDIRECT command is stored in them.
Also see file redirection.
resident programs
Programs
that are basic to McIDAS-X and its environment. For example, in McIDAS-X,
the resident program mctext controls command line input from the keyboard
and displays text output on the Text and Command Window.
resolution
See full, image,
or satellite resolution.
scheduler
The
part of the McIDAS-X system that initiates and ends user-defined command
sequences.
selection clause
A
text string used by an application to restrict information sent from the
server to the client.
sensor source
A
satellite device that collects a specific wavelength of radiation; for example,
visible, infrared, microwave, solar protons or X-ray.
sensor source number
The
number assigned to an image data source; it is stored in word 3 of the area
directory; for example, 70 is the GOES-8 imager.
sensor type
Sensor
name consisting of up to four characters, stored in word 52 of the area directory;
for example, GVAR is the sensor on GOES-8.
server
The
machine in a distributed system that stores data and supplies it to the client
upon request. Each McIDAS-X workstation session acts as both a client and
a local server. It can also be configured as a remote server, supplying data
to all clients.
server mapping table
The
table containing the list of dataset names on the server. Users assign these
names with the McIDAS-X DSSERVE command.
shared memory
A
component of the McIDAS-X environment that consists of User Common, redirect
tables and frame objects. Resident programs use it to communicate with applications.
shell script
A
program containing a set of executable commands; useful for running a series
of McIDAS-X commands outside of McIDAS-X.
sleep
An
application tells the operating system it doesn't want to be considered ready
to be dispatched for a period of time.
slot number
The
number 1, 2 or 3; allows loading of up to three navigation and calibration
modules.
spectral band
The
wavelength in which a scanning instrument measures data; for example, band
4 for the GOES-8 imager is 10.7 microns (infrared).
static data
Database
information that changes little over time. Examples include map files, station
tables, or font files.
static linking
Subprograms
included at compile/link time.
station tables
A
cross reference list of reporting stations.
stretching
See contrast
stretching and data stretching.
string
A
named character string defined by a user with the McIDAS-X TE command. A
character string can be accessed by programs using parameter retrieving functions.
It has two uses: it provides a shorthand method of entering commands and
it allows programs to access keyword values predefined by the user that are
not actually entered when the program begins. String names may contain no
more than 12 alphanumeric characters; strings may not exceed 160 characters.
string table
A
table of named character strings; useful for passing information between
commands run at different times. An individual string table may contain no
more than 256 strings.
synchronous
McIDAS-X
commands that run synchronously will run to completion before control is
returned to the original calling program. Also see asynchronous.
text output
Usually
refers to the three types of messages that applications use to communicate
status information to the user: text, error and debug messages.
Text and Command Window
The
window used for entering McIDAS-X commands, displaying command output and
showing workstation status information. When a session is started, 10 different
text frames can be displayed in this window.
toggle
Turning
on and off a McIDAS-X function, such as graphics or image frames; similar
to turning a light switch on and off.
token
The
smallest entity to which an observation may be parsed.
transaction
Any
ADDE exchange; it implies a transfer between an ADDE client and server.
transaction logging
The
record keeping done by ADDE servers for each transaction.
Unix
Multitasking
operating system originally developed by AT&T; McIDAS-X requires this
system.
User Common (UC)
A
component of the McIDAS-X shared memory that is used in applications to alter
the display and make the applications interact with each other in predictable
ways.
UTC
Coordinated
Universal Time; same as GMT (Greenwich Mean Time).
viewport
The
region of a frame to be displayed; graphics outside this region will not
appear even if drawn. Viewports are used in McIDAS-X programming to generate
graphical output in panels. Also called a clipping region.
whitespace
A
subset of the ASCII character set, including space, end-of-line, vertical tab,
horizontal tab and form-feed characters.
word
A
32-bit memory segment; a 16-bit memory segment is called a half-word; an 8-bit
memory segment is called a byte.
world coordinates
The
coordinate system as viewed by a graphics program; world coordinates may be
defined to be convenient for the application. Their purpose is to generate
attractive, properly positioned output regardless of the size of the frame.
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