targetsub - Creates variable and/or dimension subsets

SYNOPSIS

targetsub  [ parameter=value ... ]  [ inputfile outputfile ]
targetsub  [ parameter=value ... ]  [ inputfile ... directory ]

Parameters are: include_vars, target_lat, target_lon, num_lines, num_samples, instantiate.

DESCRIPTION

targetsub determines the best image data subset covering a target. Users can specify what variables to include or exclude from the subsets. Both the first and second image dimensions of these variables may be clipped as part of the subsetting process. If two image variables share a given dimension, it is assumed to be clipped in the same way for both variables.

Users specify not only the latitude and longitude of the target, but also the size of the desired subset image including the target. Every attempt is made to place the target in the center of the output subsets. However, subsets are shifted in order that the subsets fit entirely within the corresponding inputs.

Image subsets can be instantiated, a process which copies the necessary variable data from the input datasets, or uninstantiated. In the latter case, no variable data is copied from the input datasets. Instead, each output dataset contains pointers back into the corresponding input dataset for purposes of reading the variable data. See subset. Un-instantiated subsets can be instantiated using instant. See instant.

All attributes in the input datasets are carried over to the output subsets. This includes earth transform attributes, which may be modified to reflect any dimension clipping.

PARAMETERS

include_vars

List of variables to include in the output subsets. If the list is prefixed with a minus sign, the listed variables are excluded from the subsets. Wildcards * and ? are allowed. The default is to include all variables.

target_lat, target_lon

Latitude and latitude coordinates of the target, in standard format. See formats. There are no default values for target_lat or target_lon.

num_lines, num_samples

Number of lines and samples desired in the subsets. Lines represent height, while samples represent width. Both num_lines and num_samples must be greater than zero. There are no default values.

instantiate

Indicates that the variable data is to be copied over to the subsets. Valid responses are [yes and no]. The default is no.

EXAMPLES

The following example creates a subset of the dataset new7. All variables whose names begin with 'av' are included in the subset.

[1] % targetsub new7 new7.targetsub
include_vars   : char(255) ? [] av*
target_lat     : char( 15) ? 34 n
target_lon     : char( 15) ? 121 w
num_lines      : int       ? 100
num_samples    : int       ? 200
instantiate    : char(  3) ? [no]

SEE ALSO

subset, latsub, instant, datasets

NOTES

Un-instantiated subsets are useful as temporary datasets. However, users must be careful not to orphan them. For example, if Y is an un-instantiated subset of dataset Z, and Z is subsequently moved or removed, Y is left all alone.

Last Update: $Date: 1999/05/10 20:46:37 $