McIDAS Programmer's Manual
Version 2006

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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


A counting sequence that begins with zero.

A counting sequence that begins with one.


Abstract Data Distribution Environment software in McIDAS-X that lets a workstation act as a client, efficiently accessing data from multiple McIDAS-X servers.

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.

Application Program Interface.

applications program
A program that runs from the McIDAS-X command line.

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.

McIDAS-X commands that run asynchronously will return control to the original calling program before they have run to completion. Also see synchronous.


The spectral channels measured by a scanning instrument; for example, band 4 for the GOES-9 imager is 10.7 microns (infrared). Also see spectral band.

band map
Region of the line prefix that contains an ordered list of the spectral bands comprising the data portion of an image line.

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.

Describes the practice of replacing unused characters at the end of a string with spaces.

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.

Any memory storage.

An 8-bit memory segment; a 16-bit memory segment is called a half-word; a 32-bit memory segment is called a word.


The conversion of data values received from an instrument to useful, physical quantities such as temperature, radiance or albedo.

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.

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.

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.

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 block
The block containing the actual data values.

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.

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.

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.

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.

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.

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.

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.

dynamic linking
Subprograms loaded at run time.


earth coordinates
A coordinate system having its origin at the Earth's center, its x-axis through the intersection of the equator and prime meridian, its z-axis through the north pole, and its y-axis completing a right-handed system. Locations in this system may be Cartesian (distances x, y and z from the origin along each axis) or spherical (a distance from the origin or a reference radius, and two angles from the x-axis). The most common spherical form is longitude, geodetic latitude and height above the reference geoid.

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.

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 coordinates
The coordinates of a data point in an area file referenced sequentially by lines and elements. The top line and leftmost element have the file coordinates (0,0).

file redirection
The process that lets users identify the location of individual files on a workstation.

File format. McIDAS-X file formats include image, grid, point and text; non-McIDAS-X formats include HDF and NetCDF.

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.

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.

The term used in this manual to describe C procedures and functions, and Fortran functions and subroutines.


geocentric latitude
The angle between the equatorial plane and a ray through the point from the Earth's center.

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.

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.

Geostationary Meteorological Satellite.

Geosynchronous Operational Environmental Satellite.

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.

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.


A 16-bit memory segment; a 32-bit memory segment is called a word; an 8-bit memory segment is called a byte.

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.

A block of comments describing an applications purpose, its positional parameters and keywords, and other notable remarks.


Information that is usually represented as shades of gray in a two-dimensional matrix, such as satellite images, radar images or images derived from grids.

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

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.



Julian day
Calendar date based on a 365-day year, usually in the form ccyyddd; for example, 1996056 is February 25, 1996.


Alphanumeric values that provide input to a McIDAS-X command; useful for clarifying commands with many complicated options. Keywords are always followed by an equals sign or a comma and the assigned value. They are optional for most commands and can be entered in any order as long as they follow command positional parameters and precede quoted text in the command line.


Image line; each image line contains an optional line prefix and the actual data values. Lines run horizontally across a McIDAS-X frame; they are numbered from top to bottom with the top line numbered one.

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.

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.

A unique, alphanumeric name (usually a legal file name) used to ensure that two programs can't access the same resource simultaneously.

Continuous, automatic stepping through a sequence of image and/or graphics frames, much like a movie loop.


A McIDAS-X command that runs a series of McIDAS-X commands (embedded in Fortran code) in a predefined sequence.

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.

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.

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.

European geosynchronous meteorological satellite.

See pointing device.


The process of transforming image coordinates (lines and elements) to earth coordinates (latitude and longitude) and vice versa.

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.

See big-endian.

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.


Breaking down an observation into its most elementary parts.

Shared space that accepts the output of one program for input into another.

A point on a McIDAS-X frame assigned a unique pair of line and element coordinates.

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.

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.

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.


quoted text
The last part of the command that the user enters; each application can contain only one quote string. Quoted text is preceded by double quote marks (") and is most often used when strings entered by a user require whitespace.


radar data
Information related to the strength of the reflected radar signal; usually correlated with rainfall intensities. Radars use active sensors that emit short-wave radiation and sample the signals reflected back to the radar antenna. Modern radars also sense the radial component of droplet velocity.

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.

See full, image, or satellite resolution.


satellite resolution
The size of the smallest feature that the satellite's sensors can detect; this is determined by the geographic width of each scanned slice of the Earth's surface observed by the satellite. Also see full resolution and image resolution.

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.

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.

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.

Standard input.

Standard output.

See contrast stretching and data stretching.

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.

McIDAS-X commands that run synchronously will run to completion before control is returned to the original calling program. Also see asynchronous.


Transmission Control Protocol/Internet Protocol. A set of communications protocols used to network dissimilar systems. The TCP protocol controls the transfer of data. The IP protocol provides the routing mechanism.

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.

Turning on and off a McIDAS-X function, such as graphics or image frames; similar to turning a light switch on and off.

The smallest entity to which an observation may be parsed.

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.

Data type: image, grid, point or text.


See physical quantity.

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.

Coordinated Universal Time; same as GMT (Greenwich Mean Time).


validity code
Region of the line prefix that determines if data exists for an image line.

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.


weather text
Data transmitted in alphanumeric form; it can be user-generated or computer-generated and contains forecasts, observations, weather advisories or other public information.

A subset of the ASCII character set, including space, end-of-line, vertical tab, horizontal tab and form-feed characters.

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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