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Subsections

Command Line Parameters

An advanced protocol to specify command line parameters is employed by VisionX commands. It permits both positional and positionindependent parameter specification. Furthermore, it supports the pipelining of commands such that the output from one command can be fed directly into the next command without an intermediate file.

Information Parameters

This protocol is illustrated by means of an example command ``vsobel'' which is a simple edge enhancing filter command that takes and image input and produces an image result. Two enquiry parameters ``h'' and just ``'' provide information about the command. For example, to find out what parameters a command can take give

    vsobel H
    Usage: vsobel [H] [if=<inputfile>] [of=<outputfile>] [f]
    [d] [i] [e]

The H parameter lists all the possible parameters for a command. Further information can be obtained with the ``'' parameter, for example

    vsobel 
    Usage: vsobel [H] [] [help]
    [if=] infile vsobel: edge operator
    [of=] output file
    [f ] float computation option
    [d ] provide direction information
    [i ] isotropic flag
    [e ] euclidian flag

The ``'' option provides short descriptions of each parameter. It may be specified as the last parameter in a list as a shortcut for situations (often encountered) where a user has already typed several parameters but wishes to then be reminded of the full command syntax.

Value Parameters

There are two types of parameters option parameters which which are precede by a ``'', such as ``i'' above, and value parameters which have a ``='', such as ``if='' above, and require an additional value argument.

By convention, the primary input file for a command is usually associated with an ``if='' prefix and the primary output file is associated with an ``of='' prefix; such is the case with vsobel. Consider that we wish to process a file called ``image.vx'' and store the result in a file called ``edge.vx'' using the isotropic ``i'' option. This may be specified by either

    vsobel if=image.vx of=edge.vx i

    vsobel of=edge.vx i if=image.vx

This is an instance of positionindependent value parameters: the prefix identifies the parameter. This is the standard and most safe method for parameter specification.

Alternative methods for parameter specification are supported which are especially useful when the user is interactively typing commands. Value parameters may use a positional dependent syntax in which they are satisfied in order. The only exception to this is the of= parameter which may be specified by a ``o'' prefix. This is very convenient when a number of value parameters are to be specified. Therefore, the above command could also be specified by

    vsobel image.vx o edge.vx i

The mixing of value parameter types is also permitted so any of the following are equivalent

    vsobel if=image.vx o edge.vx i
    vsobel i of=edge.vx image.vx 
    vsobel o edge.vx if=image.vx i

File Redirection

Standard file direction primitives such as <, >, and | are supported such that the following are also equivalent to the above:

    vsobel o edge.vx i < image.vx
    vsobel i of= if=  < image.vx > edge.vx
    vsobel i  < image.vx > edge.vx
    vsobel if=image.vx i > edge.vx

The syntax ``if='' without an argument is used to explicitly state that the value of the argument is the standard input (second example above). Since vsobel only has one input value argument, there is no need to explicitly specify it (third example above).

Next: VXM interactive command execution Up: VisionX V4 Users Guide Previous: The VisionX Data Manager