latsub [ parameter=value ... ] [ inputfile outputfile ] latsub [ parameter=value ... ] [ inputfile ... directory ]
Parameters are: include_vars, min_lat, max_lat, one_subset, adjust_time, instantiate.
latsub determines data subsets falling in a given latitude range. This function is extremely useful when working with full-orbit satellite passes. The benefits are two-fold. First, subsetting can reduce the amount of data being processed. Secondly, reducing latitude range to less than 180 degrees makes earth location processing more well-defined.
Users can specify what variables to include or exclude from the subsets. Only the leading dimensions of these variables are clipped as part of the subsetting process. All variables with the same leading dimension are assumed to have the same earth location. When two leading dimensions differ by some integer factor (e.g., multi-resolution sensor data), latsub makes every attempt to keep these dimensions lined up in the output subsets.
Subsets can be instantiated, a process that 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.
The parameter adjust_time is used to control how attributes are modified. If adjust_time=yes, the start_time attribute is changed to reflect the subsetting process. This is very important when extracting subsets from whole orbit passes. If adjust_time=no, the built-in offset attribute of clipped leading dimensions is modified to reflect the subsetting process.
More than one subset can be extracted per input dataset. This is allowed when the parameter one_subset=no. For a given input dataset, if the name of the first output subset is outputfile, then the name of subsequent subsets would be outputfile_a, outputfile_b, etc.
If the _c suffix scheme for multiple subsets is undesireable, the setname function can be used to generate subset names without suffixes; e.g., time can be used to distinguish subsets. However, if setname is used for renaming multiple subsets, it is important to use adjust_time=yes.
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.
The following example creates a subset of a dataset new7.latsub. All variables starting with the letters 'av' are clipped.
[1] % latsub new7 new7.latsub include_vars : char(255) ? [] av* min_lat : char( 15) ? 34n max_lat : char( 15) ? 35n one_subset : char( 3) ? [yes] adjust_time : char( 3) ? [no] instantiate : char( 3) ? [no]
subset, setname, targetsub, instant, datasets
Uninstantiated 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 20:14:36 $